## Peer-reviewed publications

### 2023

- Markus Grassl. New Quantum Codes from CSS Codes.
*Quantum Information Processing*, 22, jan 2023. doi:10.1007/s11128-023-03835-3

[BibTeX] [Download PDF]`@Article{grassl_CSS_2023, author = {Grassl, Markus}, journal = {Quantum Information Processing}, title = {New Quantum Codes from {CSS} Codes}, year = {2023}, issn = {1573-1332}, month = jan, volume = {22}, OPTnumber = {86}, pages = {}, doi = {10.1007/s11128-023-03835-3}, url = {https://doi.org/10.1007/s11128-023-03835-3}, urldate = {2023-01-23} }`

### 2022

- Marcus Appleby, Ingemar Bengtsson, Markus Grassl, Michael Harrison, and Gary McConnell. SIC-POVMs from Stark units: Prime dimensions $n^2+3$.
*Journal of Mathematical Physics*, 63(11):112205, nov 2022. doi:10.1063/5.0083520

[BibTeX] [Download PDF]`@Article{grassl_SICPOVM_2022, author = {Appleby, Marcus and Bengtsson, Ingemar and Grassl, Markus and Harrison, Michael and McConnell, Gary}, journal = {Journal of Mathematical Physics}, title = {{SIC-POVMs} from {S}tark units: {P}rime dimensions $n^2+3$}, year = {2022}, issn = {0022-2488, 1089-7658}, month = nov, volume = {63}, number = {11}, pages = {112205}, doi = {10.1063/5.0083520}, url = {https://doi.org/10.1063/5.0083520}, urldate = {2022-11-08} }`

- Chenfeng Cao, Chao Zhang, Zipeng Wu, Markus Grassl, and Bei Zeng. Quantum variational learning for quantum error-correcting codes.
*Quantum*, 6:828, oct 2022. acknowledgment to ICTQT IRAP project included doi:10.22331/q-2022-10-06-828

[BibTeX] [Download PDF]`@article{Cao2022quantumvariational, doi = {10.22331/q-2022-10-06-828}, url = {https://doi.org/10.22331/q-2022-10-06-828}, title = {Quantum variational learning for quantum error-correcting codes}, author = {Cao, Chenfeng and Zhang, Chao and Wu, Zipeng and Grassl, Markus and Zeng, Bei}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {6}, pages = {828}, month = oct, year = {2022}, note = {acknowledgment to ICTQT IRAP project included} }`

- Massimiliano Incudini, Fabio Tarocco, Riccardo Mengoni, Alessandra Di Pierro, and Antonio Mandarino. Computing graph edit distance on quantum devices.
*Quantum Machine Intelligence*, 4(2):1-21, 2022. acknowledgment to ICTQT IRAP project included

[BibTeX]`@article{incudini2022computing, title={Computing graph edit distance on quantum devices}, author={Incudini, Massimiliano and Tarocco, Fabio and Mengoni, Riccardo and Di Pierro, Alessandra and Mandarino, Antonio}, journal={Quantum Machine Intelligence}, volume={4}, number={2}, pages={1--21}, year={2022}, publisher={Springer}, eprint = {arXiv:2111.10183}, note = {acknowledgment to ICTQT IRAP project included} }`

- Antonio Mandarino. Quantum Thermal Amplifiers with Engineered Dissipation.
*Entropy*, 24(8):1031, jul 2022. acknowledgment to ICTQT IRAP project included doi:10.3390/e24081031

[BibTeX] [Download PDF]`@article{Mandarino_2022, doi = {10.3390/e24081031}, url = {https://doi.org/10.3390/e24081031}, year = 2022, month = jul, publisher = {{MDPI} {AG}}, volume = {24}, number = {8}, pages = {1031}, author = {Antonio Mandarino}, title = {Quantum Thermal Amplifiers with Engineered Dissipation}, journal = {Entropy}, eprint = {arXiv:2208.12620}, note = {acknowledgment to ICTQT IRAP project included} }`

- Mariami Gachechiladze, Bartłomiej Bkak, Marcin Pawłowski, and Nikolai Miklin. Quantum Bell inequalities from Information Causality \textendash tight for Macroscopic Locality.
*Quantum*, 6:717, may 2022. acknowledgment to ICTQT IRAP project included doi:10.22331/q-2022-05-24-717

[BibTeX] [Download PDF]`@article{Gachechiladze_2022, doi = {10.22331/q-2022-05-24-717}, url = {https://doi.org/10.22331%2Fq-2022-05-24-717}, year = 2022, month = may, publisher = {Verein zur Forderung des Open Access Publizierens in den Quantenwissenschaften}, volume = {6}, pages = {717}, author = {Mariami Gachechiladze and Bart{\l}omiej B{\k{a}}k and Marcin Paw{\l}owski and Nikolai Miklin}, title = {Quantum Bell inequalities from Information Causality {\textendash} tight for Macroscopic Locality}, journal = {Quantum}, note = {acknowledgment to ICTQT IRAP project included} }`

- Łukasz Rudnicki. Geophysics and Stuart vortices on a sphere meet differential geometry.
*Communications on Pure and Applied Analysis*, 21(7):2479-2493, 2022. acknowledgment to ICTQT IRAP project included

[BibTeX]`@article{1534-0392_2022_7_2479, title = {Geophysics and Stuart vortices on a sphere meet differential geometry}, journal = {Communications on Pure and Applied Analysis}, volume = {21}, number = {7}, pages = {2479-2493}, year = {2022}, author = {Łukasz Rudnicki}, note = {acknowledgment to ICTQT IRAP project included} }`

- Thais L. Silva, Łukasz Rudnicki, Daniel S. Tasca, and Stephen P. Walborn. Discretized continuous quantum-mechanical observables that are neither continuous nor discrete.
*Phys. Rev. Research*, 4:013060, jan 2022. acknowledgment to ICTQT IRAP project included doi:10.1103/PhysRevResearch.4.013060

[BibTeX] [Download PDF]`@article{PhysRevResearch.4.013060, title = {Discretized continuous quantum-mechanical observables that are neither continuous nor discrete}, author = {Silva, Thais L. and Rudnicki, \L{}ukasz and Tasca, Daniel S. and Walborn, Stephen P.}, journal = {Phys. Rev. Research}, volume = {4}, issue = {1}, pages = {013060}, numpages = {9}, year = {2022}, month = jan, publisher = {American Physical Society}, doi = {10.1103/PhysRevResearch.4.013060}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.4.013060}, note = {acknowledgment to ICTQT IRAP project included} }`

- Paweł Horodecki, Łukasz Rudnicki, and Karol ifmmode dotZelse Żfiyczkowski. Five Open Problems in Quantum Information Theory.
*PRX Quantum*, 3:010101, mar 2022. acknowledgment to ICTQT IRAP project included doi:10.1103/PRXQuantum.3.010101

[BibTeX] [Download PDF]`@article{PRXQuantum.3.010101, title = {Five Open Problems in Quantum Information Theory}, author = {Horodecki, Pawe\l{} and Rudnicki, \L{}ukasz and \ifmmode \dot{Z}\else \.{Z}\fi{}yczkowski, Karol}, journal = {PRX Quantum}, volume = {3}, issue = {1}, pages = {010101}, numpages = {17}, year = {2022}, month = mar, publisher = {American Physical Society}, doi = {10.1103/PRXQuantum.3.010101}, url = {https://link.aps.org/doi/10.1103/PRXQuantum.3.010101}, note = {acknowledgment to ICTQT IRAP project included} }`

- Klaus Liegener and Łukasz Rudnicki. Quantum speed limit and stability of coherent states in quantum gravity.
*Classical and Quantum Gravity*, 39(12):12LT01, may 2022. acknowledgment to ICTQT IRAP project included doi:10.1088/1361-6382/ac6faa

[BibTeX] [Abstract] [Download PDF]

Utilizing the program of expectation values in coherent states and its recently developed algorithmic tools, this letter investigates the dynamical properties of cosmological coherent states for loop quantum gravity. To this end, the quantum speed limit (QSL) is adapted to quantum gravity, yielding necessary consistency checks for any proposal of stable families of states. To showcase the strength of the developed tools, they are applied to a prominent model: the Euclidean part of the quantum scalar constraint. We report the variance of this constraint evaluated on a family of coherent states showing that, for short times, this family passes the QSL test, allowing the transition from one coherent state to another one.

`@article{Liegener_2022, doi = {10.1088/1361-6382/ac6faa}, url = {https://doi.org/10.1088/1361-6382/ac6faa}, year = 2022, month = may, publisher = {{IOP} Publishing}, volume = {39}, number = {12}, pages = {12LT01}, author = {Klaus Liegener and {\L}ukasz Rudnicki}, title = {Quantum speed limit and stability of coherent states in quantum gravity}, journal = {Classical and Quantum Gravity}, abstract = {Utilizing the program of expectation values in coherent states and its recently developed algorithmic tools, this letter investigates the dynamical properties of cosmological coherent states for loop quantum gravity. To this end, the quantum speed limit (QSL) is adapted to quantum gravity, yielding necessary consistency checks for any proposal of stable families of states. To showcase the strength of the developed tools, they are applied to a prominent model: the Euclidean part of the quantum scalar constraint. We report the variance of this constraint evaluated on a family of coherent states showing that, for short times, this family passes the QSL test, allowing the transition from one coherent state to another one.}, note = {acknowledgment to ICTQT IRAP project included} }`

- Luka Ursić, Godfrey Baldacchino, Željana Bašić, Ana Belén Sainz, Ivan Buljan, Miriam Hampel, Ivana Kružić, Mia Majić, Ana Marušić, Franck Thetiot, Ružica Tokalić, and Leandra Vranješ Markić. Factors Influencing Interdisciplinary Research and Industry-Academia Collaborations at Six European Universities: A Qualitative Study.
*Sustainability*, 14(15), 2022. doi:10.3390/su14159306

[BibTeX] [Download PDF]`@Article{su14159306, AUTHOR = {Ursić, Luka and Baldacchino, Godfrey and Bašić, Željana and Sainz, Ana Belén and Buljan, Ivan and Hampel, Miriam and Kružić, Ivana and Majić, Mia and Marušić, Ana and Thetiot, Franck and Tokalić, Ružica and Markić, Leandra Vranješ}, TITLE = {Factors Influencing Interdisciplinary Research and Industry-Academia Collaborations at Six European Universities: A Qualitative Study}, JOURNAL = {Sustainability}, VOLUME = {14}, YEAR = {2022}, NUMBER = {15}, ARTICLE-NUMBER = {9306}, URL = {https://www.mdpi.com/2071-1050/14/15/9306}, ISSN = {2071-1050}, DOI = {10.3390/su14159306} }`

- Ana Belén Sainz. Q-Turn: Changing Paradigms In Quantum Science.
*Quantum Science and Technology*, 7:044004, 2022. doi:10.1088/2058-9565/ac82c4

[BibTeX]`@article{sainz2022q, title={Q-Turn: Changing Paradigms In Quantum Science}, author={Sainz, Ana Bel{\'e}n}, journal={Quantum Science and Technology}, year={2022}, volume={7}, pages={044004}, publisher={IOP Publishing}, doi={10.1088/2058-9565/ac82c4} }`

- Marcin Karczewski, Giovanni Scala, Antonio Mandarino, Ana Belén Sainz, and Marek Żukowski. Avenues to generalising Bell inequalities.
*Journal of Physics A: Mathematical and Theoretical*, 55:384011, 2022. doi:10.1088/1751-8121/ac8a28

[BibTeX]`@article{karczewski2022avenues, title={Avenues to generalising Bell inequalities}, author={Karczewski, Marcin and Scala, Giovanni and Mandarino, Antonio and Sainz, Ana Bel{\'e}n and {\.Z}ukowski, Marek}, journal={Journal of Physics A: Mathematical and Theoretical}, year={2022}, volume={55}, pages={384011}, publisher={IOP Publishing}, doi={10.1088/1751-8121/ac8a28} }`

- Vinicius P. Rossi, Matty J. Hoban, and Ana Belén Sainz. On characterising assemblages in Einstein-Podolsky-Rosen scenarios.
*Journal of Physics A: Mathematical and Theoretical*, 55:264002, 2022. doi:10.1088/1751-8121/ac7090

[BibTeX]`@article{rossi2022characterising, title={On characterising assemblages in Einstein-Podolsky-Rosen scenarios}, author={Rossi, Vinicius P and Hoban, Matty J and Sainz, Ana Bel{\'e}n}, journal={Journal of Physics A: Mathematical and Theoretical}, year={2022}, volume={55}, pages={264002}, publisher={IOP Publishing}, doi={10.1088/1751-8121/ac7090} }`

- Tanjung Krisnanda, Sanjib Ghosh, Tomasz Paterek, Wiesław Laskowski, and Timothy C. H. Liew. Phase Measurement Beyond the Standard Quantum Limit Using a Quantum Neuromorphic Platform.
*Phys. Rev. Applied*, 18:034011, sep 2022. doi:10.1103/PhysRevApplied.18.034011

[BibTeX] [Download PDF]`@article{Krisnanda2022_PhaseMeasurement, title = {Phase Measurement Beyond the Standard Quantum Limit Using a Quantum Neuromorphic Platform}, author = {Krisnanda, Tanjung and Ghosh, Sanjib and Paterek, Tomasz and Laskowski, Wies\l{}aw and Liew, Timothy C.H.}, journal = {Phys. Rev. Applied}, volume = {18}, issue = {3}, pages = {034011}, numpages = {10}, year = {2022}, month = sep, publisher = {American Physical Society}, doi = {10.1103/PhysRevApplied.18.034011}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.18.034011} }`

- Waldemar Kłobus, Paweł Kurzyifmmode acutenelse ‘nfiski, Marek Kuifmmode acuteselse ‘sfi, Wiesław Laskowski, Robert Przybycieifmmode acutenelse ‘nfi, and Karol ifmmode dotZelse Żfiyczkowski. Transition from order to chaos in reduced quantum dynamics.
*Phys. Rev. E*, 105:034201, mar 2022. doi:10.1103/PhysRevE.105.034201

[BibTeX] [Download PDF]`@article{Klobus2022_fromOrderToChaos, title = {Transition from order to chaos in reduced quantum dynamics}, author = {K\l{}obus, Waldemar and Kurzy\ifmmode \acute{n}\else \'{n}\fi{}ski, Pawe\l{} and Ku\ifmmode \acute{s}\else \'{s}\fi{}, Marek and Laskowski, Wies\l{}aw and Przybycie\ifmmode \acute{n}\else \'{n}\fi{}, Robert and \ifmmode \dot{Z}\else \.{Z}\fi{}yczkowski, Karol}, journal = {Phys. Rev. E}, volume = {105}, issue = {3}, pages = {034201}, numpages = {9}, year = {2022}, month = mar, publisher = {American Physical Society}, doi = {10.1103/PhysRevE.105.034201}, url = {https://link.aps.org/doi/10.1103/PhysRevE.105.034201} }`

- David Schmid, Haoxing Du, John H. Selby, and Matthew F. Pusey. Uniqueness of Noncontextual Models for Stabilizer Subtheories.
*Phys. Rev. Lett.*, 129:120403, sep 2022. doi:10.1103/PhysRevLett.129.120403

[BibTeX] [Download PDF]`@article{Schmid_2022_NoncontextualModels, title = {Uniqueness of Noncontextual Models for Stabilizer Subtheories}, author = {Schmid, David and Du, Haoxing and Selby, John H. and Pusey, Matthew F.}, journal = {Phys. Rev. Lett.}, volume = {129}, issue = {12}, pages = {120403}, numpages = {6}, year = {2022}, month = sep, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.129.120403}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.129.120403} }`

- Paulo J. Cavalcanti, John H. Selby, Jamie Sikora, and Ana Belén Sainz. Decomposing all multipartite non-signalling channels via quasiprobabilistic mixtures of local channels in generalised probabilistic theories.
*Journal of Physics A: Mathematical and Theoretical*, 55(40):404001, sep 2022. doi:10.1088/1751-8121/ac8ea4

[BibTeX] [Abstract] [Download PDF]

Non-signalling quantum channels—relevant in, e.g., the study of Bell and Einstein–Podolsky–Rosen scenarios—may be decomposed as an affine combinations of local operations in bipartite scenarios. Moreover, when these channels correspond to stochastic maps between classical variables, such a decomposition is possible even in multipartite scenarios. These two results have proven useful when studying the properties of these channels, such as their communication and information processing power, and even when defining measures of the non-classicality of physical phenomena (such as Bell non-classicality and steering). In this paper we show that such useful quasi-stochastic characterizations of channels may be unified and applied to the broader class of multipartite non-signalling channels. Moreover, we show that this holds for non-signalling channels in quantum theory, as well as in a larger family of generalised probabilistic theories. More precisely, we prove that channels are non-signalling if and only if they can be decomposed as an affine combinations of corresponding local operations, provided that the underlying physical theory is locally tomographic—a property that quantum theory satisfies. Our results then can be viewed as a generalisation of references (Phys. Rev. Lett. 111 170403) and (2013 Phys. Rev. A 88 022318) to the multipartite scenario for arbitrary tomographically local generalised probabilistic theories (including quantum theory). Our proof technique leverages Hardy’s duotensor formalism, highlighting its utility in this line of research.

`@article{Cavalcanti_2022, doi = {10.1088/1751-8121/ac8ea4}, url = {https://doi.org/10.1088/1751-8121/ac8ea4}, year = 2022, month = sep, publisher = {{IOP} Publishing}, volume = {55}, number = {40}, pages = {404001}, author = {Paulo J Cavalcanti and John H Selby and Jamie Sikora and Ana Bel{\'{e}}n Sainz}, title = {Decomposing all multipartite non-signalling channels via quasiprobabilistic mixtures of local channels in generalised probabilistic theories}, journal = {Journal of Physics A: Mathematical and Theoretical}, abstract = {Non-signalling quantum channels—relevant in, e.g., the study of Bell and Einstein–Podolsky–Rosen scenarios—may be decomposed as an affine combinations of local operations in bipartite scenarios. Moreover, when these channels correspond to stochastic maps between classical variables, such a decomposition is possible even in multipartite scenarios. These two results have proven useful when studying the properties of these channels, such as their communication and information processing power, and even when defining measures of the non-classicality of physical phenomena (such as Bell non-classicality and steering). In this paper we show that such useful quasi-stochastic characterizations of channels may be unified and applied to the broader class of multipartite non-signalling channels. Moreover, we show that this holds for non-signalling channels in quantum theory, as well as in a larger family of generalised probabilistic theories. More precisely, we prove that channels are non-signalling if and only if they can be decomposed as an affine combinations of corresponding local operations, provided that the underlying physical theory is locally tomographic—a property that quantum theory satisfies. Our results then can be viewed as a generalisation of references (Phys. Rev. Lett. 111 170403) and (2013 Phys. Rev. A 88 022318) to the multipartite scenario for arbitrary tomographically local generalised probabilistic theories (including quantum theory). Our proof technique leverages Hardy’s duotensor formalism, highlighting its utility in this line of research.} }`

- Thomas D. Galley, Flaminia Giacomini, and John H. Selby. A no-go theorem on the nature of the gravitational field beyond quantum theory.
*Quantum*, 6:779, aug 2022. doi:10.22331/q-2022-08-17-779

[BibTeX] [Download PDF]`@article{Galley2022nogotheoremnatureof, doi = {10.22331/q-2022-08-17-779}, url = {https://doi.org/10.22331/q-2022-08-17-779}, title = {A no-go theorem on the nature of the gravitational field beyond quantum theory}, author = {Galley, Thomas D. and Giacomini, Flaminia and Selby, John H.}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {6}, pages = {779}, month = aug, year = {2022} }`

- Paulo J. Cavalcanti, John H. Selby, Jamie Sikora, Thomas D. Galley, and Ana Belén Sainz. Post-quantum steering is a stronger-than-quantum resource for information processing.
*npj Quantum Information*, 8(1):1-10, 2022. doi:10.1038/s41534-022-00574-8

[BibTeX]`@article{cavalcanti2022post, title={Post-quantum steering is a stronger-than-quantum resource for information processing}, author={Cavalcanti, Paulo J and Selby, John H and Sikora, Jamie and Galley, Thomas D and Sainz, Ana Bel{\'e}n}, journal={npj Quantum Information}, volume={8}, number={1}, pages={1--10}, year={2022}, publisher={Nature Publishing Group}, doi={10.1038/s41534-022-00574-8} }`

- Markus Grassl, Felix Huber, and Andres Winter. Entropic Proofs of Singleton Bounds for Quantum Error-Correcting Codes.
*IEEE Transactions on Information Theory*, 68(6):3942-3950, jun 2022. doi:10.1109/TIT.2022.3149291

[BibTeX] [Download PDF]`@Article{grassl_entropic_2022, author = {Grassl, Markus and Huber, Felix and Winter, Andres}, journal = {IEEE Transactions on Information Theory}, title = {Entropic Proofs of {S}ingleton Bounds for Quantum Error-Correcting Codes}, year = {2022}, issn = {0018-9448, 1557-9654}, month = jun, volume = {68}, number = {6}, pages = {3942-3950}, doi = {10.1109/TIT.2022.3149291}, language = {en}, url = {https://doi.org/10.1109/TIT.2022.3149291}, urldate = {2021-05-19} }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Żukowski. Remarks about Bell-nonclassicality of a single photon.
*Physics Letters A*, 435:128031, 2022. doi:https://doi.org/10.1016/j.physleta.2022.128031

[BibTeX] [Abstract] [Download PDF]

We discuss the interferometric scheme put forward by Tan, Walls, and Collett (TWC) that claims to reveal Bell non-classicality of a single photon. We show that the violation of local realism they report hinges on an additional assumption about hidden variables. Without it, one can construct a classical model that correctly predicts all the probabilities of the TWC scheme. To illustrate this, we construct a proper Bell inequality, devoid of additional assumptions, that is not violated by the TWC setup. We then show a modification of the interferometric scheme, consisting in making the amplitude of auxiliary fields tunable, that enables the Bell violation. Finally, we present an alternative point of view on the shortcomings of the original TWC analysis, arguing that it effectively treats the weak coherent states classically.

`@article{DAS2022128031, title = {Remarks about {Bell}-nonclassicality of a single photon}, journal = {Physics Letters A}, volume = {435}, pages = {128031}, year = {2022}, issn = {0375-9601}, doi = {https://doi.org/10.1016/j.physleta.2022.128031}, url = {https://www.sciencedirect.com/science/article/pii/S037596012200113X}, author = {Tamoghna Das and Marcin Karczewski and Antonio Mandarino and Marcin Markiewicz and Bianka Woloncewicz and Marek Żukowski}, keywords = {Bell's theorem, Single photon, Local hidden variable model}, abstract = {We discuss the interferometric scheme put forward by Tan, Walls, and Collett (TWC) that claims to reveal Bell non-classicality of a single photon. We show that the violation of local realism they report hinges on an additional assumption about hidden variables. Without it, one can construct a classical model that correctly predicts all the probabilities of the TWC scheme. To illustrate this, we construct a proper Bell inequality, devoid of additional assumptions, that is not violated by the TWC setup. We then show a modification of the interferometric scheme, consisting in making the amplitude of auxiliary fields tunable, that enables the Bell violation. Finally, we present an alternative point of view on the shortcomings of the original TWC analysis, arguing that it effectively treats the weak coherent states classically.}, urldate={2022-03-31} }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Zukowski. Comment on `Single particle nonlocality with completely independent reference states’.
*New Journal of Physics*, 24(3):038001, mar 2022. doi:10.1088/1367-2630/ac55b1

[BibTeX] [Abstract] [Download PDF]

We comment on the purported violation of local realism, by a single photon induced correlations between homodyne detectors, which one can find in: (2008) New J. Phys. 10 113024 [arXiv:0807.0109]. The claim is erroneous, due to a calculational mistake. As the result is the basis of other claims in the paper, they are unsubstantiated.

`@article{Das2022, title = {Comment on `{Single} particle nonlocality with completely independent reference states'}, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Zukowski, Marek}, doi = {10.1088/1367-2630/ac55b1}, url = {https://doi.org/10.1088/1367-2630/ac55b1}, year = 2022, month = mar, publisher = {{IOP} Publishing}, volume = {24}, number = {3}, pages = {038001}, journal = {New Journal of Physics}, abstract = {We comment on the purported violation of local realism, by a single photon induced correlations between homodyne detectors, which one can find in: (2008) New J. Phys. 10 113024 [arXiv:0807.0109]. The claim is erroneous, due to a calculational mistake. As the result is the basis of other claims in the paper, they are unsubstantiated.}, eprint = {arXiv:2107.07951}, urldate={2022-03-31} }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Żukowski. Wave–particle complementarity: detecting violation of local realism with photon-number resolving weak-field homodyne measurements.
*New Journal of Physics*, 24(3):033017, 2022. doi:10.1088/1367-2630/ac54c8

[BibTeX] [Download PDF]`@article{das2022wave, title={Wave--particle complementarity: detecting violation of local realism with photon-number resolving weak-field homodyne measurements}, author={Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and {\.Z}ukowski, Marek}, journal={New Journal of Physics}, volume={24}, number={3}, pages={033017}, year={2022}, publisher={IOP Publishing}, url={https://doi.org/10.1088/1367-2630/ac54c8}, doi={10.1088/1367-2630/ac54c8}, urldate={2022-03-31}, eprint = {arXiv:2104.10703} }`

- Karol Horodecki, Marek Winczewski, and Siddhartha Das. Fundamental limitations on the device-independent quantum conference key agreement.
*Physical Review A*, 105(2), feb 2022. doi:10.1103/physreva.105.022604

[BibTeX] [Download PDF]`@article{Horodecki_2022, doi = {10.1103/physreva.105.022604}, url = {http://dx.doi.org/10.1103/PhysRevA.105.022604}, year = 2022, month = feb, publisher = {American Physical Society ({APS})}, volume = {105}, number = {2}, author = {Karol Horodecki and Marek Winczewski and Siddhartha Das}, title = {Fundamental limitations on the device-independent quantum conference key agreement}, journal = {Physical Review A} }`

- Konrad Schlichtholz, Bianka Woloncewicz, and Marek Żukowski. Simplified quantum optical Stokes observables and Bell’s theorem.
*Scientific reports*, 12(1):1-9, 2022. doi:https://doi.org/10.1038/s41598-022-14232-8

[BibTeX] [Download PDF]`@article{schlichtholz2021simplified, title={Simplified quantum optical Stokes observables and Bell’s theorem}, author={Schlichtholz, Konrad and Woloncewicz, Bianka and {\.Z}ukowski, Marek}, journal={Scientific reports}, volume={12}, number={1}, pages={1--9}, year={2022}, publisher={Nature Publishing Group}, doi={https://doi.org/10.1038/s41598-022-14232-8}, url={https://www.nature.com/articles/s41598-022-14232-8} }`

- Marcin Łobejko. *Work and Fluctuations: Coherent vs. Incoherent Ergotropy Extraction.
*Quantum*, 6:762, jul 2022. doi:10.22331/q-2022-07-14-762

[BibTeX] [Download PDF]`@article{Lobejko2022workfluctuations, doi = {10.22331/q-2022-07-14-762}, url = {https://doi.org/10.22331/q-2022-07-14-762}, title = {*Work and {F}luctuations: {C}oherent vs. {I}ncoherent {E}rgotropy {E}xtraction}, author = {{\L{}}obejko, Marcin}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {6}, pages = {762}, month = jul, year = {2022} }`

- Seeta Vasudevrao, H. S. Karthik, I. Reena, Sudha, and A. R. Usha Devi. Margenau–Hill operator valued measures and joint measurability.
*International Journal of Quantum Information*, 20:2250023, 2022. doi:10.1142/S021974992250023X

[BibTeX] [Download PDF]`@article{Vasudevrao2022margenau-hill, doi = {10.1142/S021974992250023X}, url = {https://doi.org/10.1142/S021974992250023X}, title = {Margenau–Hill operator valued measures and joint measurability}, author = {Vasudevrao, Seeta and Karthik, H.S. and Reena, I. and Sudha and Usha Devi, A.R.}, journal = {{International Journal of Quantum Information}}, issn = {1793-6918}, publisher = {{World Scientific}}, volume = {20}, pages = {2250023}, month = {}, year = {2022} }`

- B. Zjawin, M. Bober, R. Ciuryło, D. Lisak, M. Zawada, and P. Wcisło. Engineering the sensitivity of macroscopic physical systems to variations in the fine-structure constant.
*Europhysics Letters*, 136(5):58001, 2022.

[BibTeX] [Abstract] [Download PDF]

Experiments aimed at searching for variations in the fine-structure constant α are based on spectroscopy of transitions in microscopic bound systems, such as atoms and ions, or resonances in optical cavities. The sensitivities of these systems to variations in α are typically on the order of unity and are fixed for a given system. For heavy atoms, highly charged ions and nuclear transitions, the sensitivity can be increased by benefiting from the relativistic effects and favorable arrangement of quantum states. This article proposes a new method for controlling the sensitivity factor of macroscopic physical systems. Specific concepts of optical cavities with tunable sensitivity to α are described. These systems show qualitatively different properties from those of previous studies of the sensitivity of macroscopic systems to variations in α, in which the sensitivity was found to be fixed and fundamentally limited to an order of unity. Although possible experimental constraints attainable with the specific optical cavity arrangements proposed in this article do not yet exceed the present best constraints on α variations, this work paves the way for developing new approaches to searching for variations in the fundamental constants of physics.

`@article{zjawin2022engineering, title={Engineering the sensitivity of macroscopic physical systems to variations in the fine-structure constant}, author={Zjawin, B and Bober, M and Ciury{\l}o, R and Lisak, D and Zawada, M and Wcis{\l}o, P}, journal={Europhysics Letters}, volume={136}, number={5}, pages={58001}, year={2022}, publisher={IOP Publishing}, abstract = {Experiments aimed at searching for variations in the fine-structure constant α are based on spectroscopy of transitions in microscopic bound systems, such as atoms and ions, or resonances in optical cavities. The sensitivities of these systems to variations in α are typically on the order of unity and are fixed for a given system. For heavy atoms, highly charged ions and nuclear transitions, the sensitivity can be increased by benefiting from the relativistic effects and favorable arrangement of quantum states. This article proposes a new method for controlling the sensitivity factor of macroscopic physical systems. Specific concepts of optical cavities with tunable sensitivity to α are described. These systems show qualitatively different properties from those of previous studies of the sensitivity of macroscopic systems to variations in α, in which the sensitivity was found to be fixed and fundamentally limited to an order of unity. Although possible experimental constraints attainable with the specific optical cavity arrangements proposed in this article do not yet exceed the present best constraints on α variations, this work paves the way for developing new approaches to searching for variations in the fundamental constants of physics.}, url = {https://iopscience.iop.org/article/10.1209/0295-5075/ac3da3/pdf}, }`

- I. Reena, H. S. Karthik, Prabhu J. Tej, Sudha, Usha A. R. Devi, and A. K. Rajagopal. Local sum uncertainty relations for angular momentum operators of bipartite permutation symmetric systems.
*Chinese Physics B*, 31:060301, may 2022. doi:10.1088/1674-1056/ac5fa3

[BibTeX] [Download PDF]`@Article{reenaetal_localsumuncertainty_2022, doi = {10.1088/1674-1056/ac5fa3}, url = {https://doi.org/10.1088/1674-1056/ac5fa3}, title = {Local sum uncertainty relations for angular momentum operators of bipartite permutation symmetric systems}, author = {I Reena and H S Karthik and J Prabhu Tej and Sudha and A R Usha Devi and A K Rajagopal}, journal = {{Chinese Physics B}}, issn = {}, publisher = {{IOP Publising}}, volume = {31}, pages = {060301}, month = may, year = {2022}, }`

- A. R. Usha Devi, Sudha, I. Reena, H. S. Karthik, and A. K. Rajagopal. Quantum Correlations in Symmetric Multiqubit Systems.
*Journal of the Indian Institute of Science*, 2022. doi:10.1007/s41745-022-00323-y

[BibTeX] [Download PDF]`@Article{Ushadevietal_quantumcorrelations_2022, doi = {10.1007/s41745-022-00323-y}, url = {https://doi.org/10.1007/s41745-022-00323-y}, title = {Quantum Correlations in Symmetric Multiqubit Systems}, author = {Usha Devi, A R and Sudha and Reena, I and Karthik, H S and Rajagopal, A K}, journal = {{Journal of the Indian Institute of Science}}, issn = {}, publisher = {{Springer Nature}}, volume = {}, pages = {}, month = {}, year = {2022}, }`

- Francesco V. Pepe, Giovanni Scala, Gabriele Chilleri, Danilo Triggiani, Yoon-Ho Kim, and Vincenzo Tamma. Distance sensitivity of thermal light second-order interference beyond spatial coherence.
*The European Physical Journal Plus*, 137(6):1-10, 2022.

[BibTeX]`@article{pepe2022distance, title={Distance sensitivity of thermal light second-order interference beyond spatial coherence}, author={Pepe, Francesco V and Scala, Giovanni and Chilleri, Gabriele and Triggiani, Danilo and Kim, Yoon-Ho and Tamma, Vincenzo}, journal={The European Physical Journal Plus}, volume={137}, number={6}, pages={1--10}, year={2022}, publisher={Springer} }`

- Michał Banacki, Piotr Mironowicz, Ravishankar Ramanathan, and Paweł Horodecki. Hybrid no-signaling-quantum correlations.
*New Journal of Physics*, 24(8):083003, aug 2022. acknowledgement for ICTQT IRAP included doi:10.1088/1367-2630/ac7fb3

[BibTeX] [Abstract] [Download PDF]

Fundamental investigations in non-locality have shown that while the no-signaling principle alone is not sufficient to single out the set of quantum non-local correlations, local quantum mechanics and no-signaling together exactly reproduce the set of quantum correlations in the two-party Bell scenario. Here, we introduce and study an intermediate hybrid no-signaling quantum set of non-local correlations that we term \textbfHNSQ in the multi-party Bell scenario where some subsystems are locally quantum while the remaining subsystems are only constrained by the no-signaling principle. Specifically, the set \textbfHNSQ is a super-quantum set of correlations derived from no-signaling assemblages by performing quantum measurements on the trusted subsystems. We show that in contrast to the set \textbfNS of no-signaling behaviors, there exist extreme points of \textbfHNSQ in the tripartite Bell scenario that admit quantum realization. As a tool for optimization over the set \textbfHNSQ, we introduce an outer hierarchy of semi-definite programming approximations to the set following an approach put forward by Doherty–Parrilo–Spedalieri. We perform an extensive numerical analysis of the maximal violation of the facet Bell inequalities in the three-party binary input–output scenario and study the corresponding self-testing properties. In contrast to the usual no-signaling correlations, the new set allows for simple security proofs of (one-sided)-device-independent applications against super-quantum adversaries.

`@Article{banacki_hybrid_2022, author = {Banacki, Michał and Mironowicz, Piotr and Ramanathan, Ravishankar and Horodecki, Paweł}, journal = {New Journal of Physics}, title = {Hybrid no-signaling-quantum correlations}, note = {acknowledgement for ICTQT IRAP included}, year = {2022}, month = aug, number = {8}, pages = {083003}, volume = {24}, abstract = {Fundamental investigations in non-locality have shown that while the no-signaling principle alone is not sufficient to single out the set of quantum non-local correlations, local quantum mechanics and no-signaling together exactly reproduce the set of quantum correlations in the two-party Bell scenario. Here, we introduce and study an intermediate hybrid no-signaling quantum set of non-local correlations that we term \textbf{HNSQ} in the multi-party Bell scenario where some subsystems are locally quantum while the remaining subsystems are only constrained by the no-signaling principle. Specifically, the set \textbf{HNSQ} is a super-quantum set of correlations derived from no-signaling assemblages by performing quantum measurements on the trusted subsystems. We show that in contrast to the set \textbf{NS} of no-signaling behaviors, there exist extreme points of \textbf{HNSQ} in the tripartite Bell scenario that admit quantum realization. As a tool for optimization over the set \textbf{HNSQ}, we introduce an outer hierarchy of semi-definite programming approximations to the set following an approach put forward by Doherty–Parrilo–Spedalieri. We perform an extensive numerical analysis of the maximal violation of the facet Bell inequalities in the three-party binary input–output scenario and study the corresponding self-testing properties. In contrast to the usual no-signaling correlations, the new set allows for simple security proofs of (one-sided)-device-independent applications against super-quantum adversaries.}, groups = {Pawel_H}, doi = {10.1088/1367-2630/ac7fb3}, keywords = {Quantum Physics}, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ac7fb3}, }`

- Fattah Sakuldee and Łukasz Cywi’nski. Statistics of projective measurement on a quantum probe as a witness of noncommutativity of algebra of a probed system.
*Quantum Information Processing*, 21(7), jul 2022. acknowledgment to ICTQT IRAP project included doi:10.1007/s11128-022-03576-9

[BibTeX] [Download PDF]`@article{Sakuldee2022a, doi = {10.1007/s11128-022-03576-9}, url = {https://doi.org/10.1007/s11128-022-03576-9}, year = {2022}, month = jul, publisher = {Springer Science and Business Media {LLC}}, volume = {21}, number = {7}, author = {Fattah Sakuldee and {\L}ukasz Cywi{\'{n}}ski}, title = {Statistics of projective measurement on a quantum probe as a witness of noncommutativity of algebra of a probed system}, journal = {Quantum Information Processing}, note = {acknowledgment to ICTQT IRAP project included} }`

- Fattah Sakuldee, Philip Taranto, and Simon Milz. Connecting commutativity and classicality for multitime quantum processes.
*Physical Review A*, 106(2), aug 2022. acknowledgment to ICTQT IRAP project included doi:10.1103/physreva.106.022416

[BibTeX] [Download PDF]`@article{Sakuldee2022b, doi = {10.1103/physreva.106.022416}, url = {https://doi.org/10.1103/physreva.106.022416}, year = {2022}, month = aug, publisher = {American Physical Society ({APS})}, volume = {106}, number = {2}, author = {Fattah Sakuldee and Philip Taranto and Simon Milz}, title = {Connecting commutativity and classicality for multitime quantum processes}, journal = {Physical Review A}, note = {acknowledgment to ICTQT IRAP project included} }`

- Pedro R. Dieguez, Jéferson R. Guimar~aes, John PS Peterson, Renato M. Angelo, and Roberto M. Serra. Experimental assessment of physical realism in a quantum-controlled device.
*Communications Physics*, 5(1):1-8, 2022. doi:10.1038/s42005-022-00828-z

[BibTeX] [Download PDF]`@article{dieguez2022experimental, title={Experimental assessment of physical realism in a quantum-controlled device}, author={Dieguez, Pedro R and Guimar{\~a}es, J{\'e}ferson R and Peterson, John PS and Angelo, Renato M and Serra, Roberto M}, journal={Communications Physics}, volume={5}, number={1}, pages={1--8}, year={2022}, doi={10.1038/s42005-022-00828-z}, url={https://doi.org/10.1038/s42005-022-00828-z}, publisher={Nature Publishing Group} }`

- VS Gomes, PR Dieguez, and HM Vasconcelos. Realism-based nonlocality: Invariance under local unitary operations and asymptotic decay for thermal correlated states.
*Physica A: Statistical Mechanics and its Applications*, page 127568, 2022. doi:10.1016/j.physa.2022.127568

[BibTeX] [Download PDF]`@article{gomes2022realism, title={Realism-based nonlocality: Invariance under local unitary operations and asymptotic decay for thermal correlated states}, author={Gomes, VS and Dieguez, PR and Vasconcelos, HM}, journal={Physica A: Statistical Mechanics and its Applications}, pages={127568}, year={2022}, doi={10.1016/j.physa.2022.127568}, url={https://doi.org/10.1016/j.physa.2022.127568}, publisher={Elsevier} }`

- V. F. Lisboa, P. R. Dieguez, J. R. Guimar~aes, J. F. G. Santos, and R. M. Serra. Experimental investigation of a quantum heat engine powered by generalized measurements.
*Phys. Rev. A*, 106:022436, aug 2022. doi:10.1103/PhysRevA.106.022436

[BibTeX] [Download PDF]`@article{PhysRevA.106.022436, title = {Experimental investigation of a quantum heat engine powered by generalized measurements}, author = {Lisboa, V. F. and Dieguez, P. R. and Guimar\~aes, J. R. and Santos, J. F. G. and Serra, R. M.}, journal = {Phys. Rev. A}, volume = {106}, issue = {2}, pages = {022436}, numpages = {8}, year = {2022}, month = aug, publisher = {American Physical Society}, doi = {10.1103/PhysRevA.106.022436}, url = {https://link.aps.org/doi/10.1103/PhysRevA.106.022436} }`

- Michał Eckstein and Paweł Horodecki. Probing the limits of quantum theory with quantum information at subnuclear scales.
*Proc. R. Soc. A.*, 478:20210806, mar 2022. acknowledgement for ICTQT IRAP included doi:10.1098/rspa.2021.0806

[BibTeX] [Abstract] [Download PDF]

Modern quantum engineering techniques enabled successful foundational tests of quantum mechanics. Yet, the universal validity of quantum postulates is an open question. Here we propose a new theoretical framework of Q-data tests, which recognizes the established validity of quantum theory, but allows for more general—‘post-quantum’—scenarios in certain physical regimes. It can accommodate a large class of models with modified quantum wave dynamics, correlations beyond entanglement or general probabilistic postulates. We discuss its experimental implementation suited to probe the nature of strong nuclear interactions. In contrast to the present accelerator experiments, it shifts the focus from high-luminosity beam physics to individual particle coherent control.

`@article{Eckstein_probing_2022, doi = {10.1098/rspa.2021.0806}, url = {https://royalsocietypublishing.org/doi/abs/10.1098/rspa.2021.0806}, year = 2022, month = mar, volume = {478}, pages = {20210806}, author = {Eckstein, Micha{\l} and Horodecki, Pawe{\l}}, title = {Probing the limits of quantum theory with quantum information at subnuclear scales}, note= {acknowledgement for ICTQT IRAP included}, journal = {Proc. R. Soc. A.}, abstract = {Modern quantum engineering techniques enabled successful foundational tests of quantum mechanics. Yet, the universal validity of quantum postulates is an open question. Here we propose a new theoretical framework of Q-data tests, which recognizes the established validity of quantum theory, but allows for more general—‘post-quantum’—scenarios in certain physical regimes. It can accommodate a large class of models with modified quantum wave dynamics, correlations beyond entanglement or general probabilistic postulates. We discuss its experimental implementation suited to probe the nature of strong nuclear interactions. In contrast to the present accelerator experiments, it shifts the focus from high-luminosity beam physics to individual particle coherent control.}, groups = {Pawel_H}, }`

- Erik Aurell, Michał Eckstein, and Paweł Horodecki. Hawking radiation and the quantum marginal problem.
*Journal of Cosmology and Astroparticle Physics*, 2022(01):014, jan 2022. acknowledgement for ICTQT IRAP included doi:10.1088/1475-7516/2022/01/014

[BibTeX] [Abstract] [Download PDF]

In 1974 Steven Hawking showed that black holes emit thermal radiation, which eventually causes them to evaporate. The problem of the fate of information in this process is known as the “black hole information paradox”. Two main types of resolution postulate either a fundamental loss of information in Nature — hence the breakdown of quantum mechanics — or some sort of new physics, e.g. quantum gravity, which guarantee the global preservation of unitarity. Here we explore the second possibility with the help of recent developments in continuous-variable quantum information. Concretely, we employ the solution to the Gaussian quantum marginal problem to show that the thermality of all individual Hawking modes is consistent with a global pure state of the radiation. Surprisingly, we find out that the mods of radiation of an astrophysical black hole are thermal until the very last burst. In contrast, the single-mode thermality of Hawking radiation originating from microscopic black holes, expected to evaporate through several quanta, is not excluded, though there are constraints on modes’ frequencies. Our result paves the way towards a systematic study of multi-mode correlations in Hawking radiation.

`@article{Aurell__hawking_2022, doi = {10.1088/1475-7516/2022/01/014}, url = {https://doi.org/10.1088/1475-7516/2022/01/014}, year = 2022, month = jan, publisher = {{IOP} Publishing}, volume = {2022}, number = {01}, pages = {014}, author = {Aurell, Erik and Eckstein, Micha{\l} and Horodecki, Pawe{\l}}, title = {Hawking radiation and the quantum marginal problem}, note= {acknowledgement for ICTQT IRAP included}, journal = {Journal of Cosmology and Astroparticle Physics}, abstract = {In 1974 Steven Hawking showed that black holes emit thermal radiation, which eventually causes them to evaporate. The problem of the fate of information in this process is known as the “black hole information paradox”. Two main types of resolution postulate either a fundamental loss of information in Nature — hence the breakdown of quantum mechanics — or some sort of new physics, e.g. quantum gravity, which guarantee the global preservation of unitarity. Here we explore the second possibility with the help of recent developments in continuous-variable quantum information. Concretely, we employ the solution to the Gaussian quantum marginal problem to show that the thermality of all individual Hawking modes is consistent with a global pure state of the radiation. Surprisingly, we find out that the mods of radiation of an astrophysical black hole are thermal until the very last burst. In contrast, the single-mode thermality of Hawking radiation originating from microscopic black holes, expected to evaporate through several quanta, is not excluded, though there are constraints on modes' frequencies. Our result paves the way towards a systematic study of multi-mode correlations in Hawking radiation.}, groups = {Pawel_H}, }`

- Piotr Mironowicz, Paweł Horodecki, and Ryszard Horodecki. Non-Perfect Propagation of Information to a Noisy Environment with Self-Evolution.
*Entropy*, 24(4), mar 2022. acknowledgement for ICTQT IRAP included doi:10.3390/e24040467

[BibTeX] [Abstract] [Download PDF]

We study the non-perfect propagation of information for evolving a low-dimensional environment that includes self-evolution as well as noisy initial states and analyse the interrelations between the degree of objectivization and environment parameters. In particular, we consider an analytical model of three interacting qubits and derive its objectivity parameters. The numerical analysis shows that the quality of the spectrum broadcast structure formed during the interaction may exhibit non-monotonicity both in the speed of self-dynamics of the environment as well as its mixedness. The former effect is particularly strong, showing that—considering part of the environment as a measurement apparatus—an increase of the external magnetic field acting on the environment may turn the vague measurement into close to ideal. The above effects suggest that quantum objectivity may appear after increasing the dynamics of the environment, although not with respect to the pointer basis, but some other, which we call the generalized pointer or indicator basis. Furthermore, it seems also that, when the objectivity is poor, it may be improved, at least by some amount, by increasing the thermal noise. We provide further evidence of this by analysing the upper bounds on distance to the set of states representing perfect objectivity in the case of a higher number of qubits.

`@article{Mironowicz_non-perfect_2022, author = {Mironowicz, Piotr and Horodecki, Paweł and Horodecki, Ryszard}, title = {Non-Perfect Propagation of Information to a Noisy Environment with Self-Evolution}, note= {acknowledgement for ICTQT IRAP included}, journal = {Entropy}, volume = {24}, year = {2022}, month = mar, number = {4}, article-number = {467}, url = {https://www.mdpi.com/1099-4300/24/4/467}, PubMedID = {35455130}, ISSN = {1099-4300}, abstract = {We study the non-perfect propagation of information for evolving a low-dimensional environment that includes self-evolution as well as noisy initial states and analyse the interrelations between the degree of objectivization and environment parameters. In particular, we consider an analytical model of three interacting qubits and derive its objectivity parameters. The numerical analysis shows that the quality of the spectrum broadcast structure formed during the interaction may exhibit non-monotonicity both in the speed of self-dynamics of the environment as well as its mixedness. The former effect is particularly strong, showing that—considering part of the environment as a measurement apparatus—an increase of the external magnetic field acting on the environment may turn the vague measurement into close to ideal. The above effects suggest that quantum objectivity may appear after increasing the dynamics of the environment, although not with respect to the pointer basis, but some other, which we call the generalized pointer or indicator basis. Furthermore, it seems also that, when the objectivity is poor, it may be improved, at least by some amount, by increasing the thermal noise. We provide further evidence of this by analysing the upper bounds on distance to the set of states representing perfect objectivity in the case of a higher number of qubits.}, groups = {Pawel_H}, doi = {10.3390/e24040467}, }`

- Ravishankar Ramanathan, Yuan Liu, and Paweł Horodecki. *Large violations in Kochen Specker contextuality and their applications.
*New Journal of Physics*, 24(3):033035, mar 2022. doi:10.1088/1367-2630/ac3a84

[BibTeX] [Download PDF]`@article{Ramanathan_large_2022, title = {*Large violations in Kochen Specker contextuality and their applications}, author = {Ramanathan, Ravishankar and Liu, Yuan and Horodecki, Pawe\l{}}, journal = {New Journal of Physics}, volume = {24}, number = {3}, pages = {033035}, year = {2022}, month = mar, groups = {Pawel_H}, doi = {10.1088/1367-2630/ac3a84}, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ac3a84}, }`

- Sahil Gopalkrishna Naik, Edwin Peter Lobo, Samrat Sen, Ram Krishna Patra, Mir Alimuddin, Tamal Guha, Some Sankar Bhattacharya, and Manik Banik. Composition of Multipartite Quantum Systems: Perspective from Timelike Paradigm.
*Phys. Rev. Lett.*, 128:140401, apr 2022. acknowledgement for ICTQT IRAP included doi:10.1103/PhysRevLett.128.140401

[BibTeX] [Abstract] [Download PDF]

Figuring out the physical rationale behind natural selection of quantum theory is one of the most acclaimed quests in quantum foundational research. This pursuit has inspired several axiomatic initiatives to derive a mathematical formulation of the theory by identifying the general structure of state and effect space of individual systems as well as specifying their composition rules. This generic framework can allow several consistent composition rules for a multipartite system even when state and effect cones of individual subsystems are assumed to be quantum. Nevertheless, for any bipartite system, none of these compositions allows beyond quantum spacelike correlations. In this Letter, we show that such bipartite compositions can admit stronger-than-quantum correlations in the timelike domain and, hence, indicates pragmatically distinct roles carried out by state and effect cones. We discuss consequences of such correlations in a communication task, which accordingly opens up a possibility of testing the actual composition between elementary quanta.

`@article{Naik_composition_2022, title = {Composition of Multipartite Quantum Systems: Perspective from Timelike Paradigm}, author = {Naik, Sahil Gopalkrishna and Lobo, Edwin Peter and Sen, Samrat and Patra, Ram Krishna and Alimuddin, Mir and Guha, Tamal and Bhattacharya, Some Sankar and Banik, Manik}, note= {acknowledgement for ICTQT IRAP included}, journal = {Phys. Rev. Lett.}, volume = {128}, issue = {14}, pages = {140401}, numpages = {7}, year = {2022}, month = apr, abstract={Figuring out the physical rationale behind natural selection of quantum theory is one of the most acclaimed quests in quantum foundational research. This pursuit has inspired several axiomatic initiatives to derive a mathematical formulation of the theory by identifying the general structure of state and effect space of individual systems as well as specifying their composition rules. This generic framework can allow several consistent composition rules for a multipartite system even when state and effect cones of individual subsystems are assumed to be quantum. Nevertheless, for any bipartite system, none of these compositions allows beyond quantum spacelike correlations. In this Letter, we show that such bipartite compositions can admit stronger-than-quantum correlations in the timelike domain and, hence, indicates pragmatically distinct roles carried out by state and effect cones. We discuss consequences of such correlations in a communication task, which accordingly opens up a possibility of testing the actual composition between elementary quanta.}, publisher = {American Physical Society}, groups = {Pawel_H}, doi = {10.1103/PhysRevLett.128.140401}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.128.140401}, }`

- Samrat Sen, Edwin Peter Lobo, Sahil Gopalkrishna Naik, Ram Krishna Patra, Tathagata Gupta, Subhendu B. Ghosh, Sutapa Saha, Mir Alimuddin, Tamal Guha, Some Sankar Bhattacharya, and Manik Banik. Local quantum state marking.
*Phys. Rev. A*, 105:032407, mar 2022. acknowledgement for ICTQT IRAP included doi:10.1103/PhysRevA.105.032407

[BibTeX] [Abstract] [Download PDF]

We propose the task of local state marking (LSM), where some multipartite quantum states chosen randomly from a known set of states are distributed among spatially separated parties without revealing the identities of the individual states. The collaborative aim of the parties is to correctly mark the identities of states under the restriction that they can perform only local quantum operations (LOs) on their respective subsystems and can communicate with each other classically (CC)—popularly known as the operational paradigm of LOCC. While mutually orthogonal states can always be marked exactly under global operations, this is in general not the case under LOCC. We show that the LSM task is distinct from the vastly explored task of local state distinguishability (LSD)—perfect LSD always implies perfect LSM, whereas we establish that the converse does not hold in general. We also explore entanglement-assisted marking of states that are otherwise locally unmarkable, and we report intriguing entanglement-assisted catalytic LSM phenomena.

`@article{Sen_local_2022, title = {Local quantum state marking}, author = {Sen, Samrat and Lobo, Edwin Peter and Naik, Sahil Gopalkrishna and Patra, Ram Krishna and Gupta, Tathagata and Ghosh, Subhendu B. and Saha, Sutapa and Alimuddin, Mir and Guha, Tamal and Bhattacharya, Some Sankar and Banik, Manik}, note= {acknowledgement for ICTQT IRAP included}, journal = {Phys. Rev. A}, volume = {105}, issue = {3}, pages = {032407}, numpages = {10}, year = {2022}, month = mar, abstract={We propose the task of local state marking (LSM), where some multipartite quantum states chosen randomly from a known set of states are distributed among spatially separated parties without revealing the identities of the individual states. The collaborative aim of the parties is to correctly mark the identities of states under the restriction that they can perform only local quantum operations (LOs) on their respective subsystems and can communicate with each other classically (CC)—popularly known as the operational paradigm of LOCC. While mutually orthogonal states can always be marked exactly under global operations, this is in general not the case under LOCC. We show that the LSM task is distinct from the vastly explored task of local state distinguishability (LSD)—perfect LSD always implies perfect LSM, whereas we establish that the converse does not hold in general. We also explore entanglement-assisted marking of states that are otherwise locally unmarkable, and we report intriguing entanglement-assisted catalytic LSM phenomena.}, publisher = {American Physical Society}, groups = {Pawel_H}, doi = {10.1103/PhysRevA.105.032407}, url = {https://link.aps.org/doi/10.1103/PhysRevA.105.032407}, }`

### 2021

- Markus Grassl. Algebraic quantum codes: linking quantum mechanics and discrete mathematics.
*International Journal of Computer Mathematics: Computer Systems Theory*, 6(4):243-250, dec 2021. doi:10.1080/23799927.2020.1850530

[BibTeX] [Download PDF]`@Article{grassl_algebraic_2021, author = {Grassl, Markus}, journal = {International {J}ournal of {C}omputer {M}athematics: {C}omputer {S}ystems {T}heory}, title = {Algebraic quantum codes: linking quantum mechanics and discrete mathematics}, year = {2021}, issn = {2379-9927, 2379-9935}, month = dec, volume = {6}, number = {4}, pages = {243-250}, doi = {10.1080/23799927.2020.1850530}, language = {en}, shorttitle = {Algebraic quantum codes}, url = {https://www.tandfonline.com/doi/full/10.1080/23799927.2020.1850530}, urldate = {2021-05-10} }`

- Victoria J. Wright and Stefan Weigert. General Probabilistic Theories with a Gleason-type Theorem.
*Quantum*, 5:588, nov 2021. doi:10.22331/q-2021-11-25-588

[BibTeX] [Download PDF]`@article{Wright2021general, doi = {10.22331/q-2021-11-25-588}, url = {https://doi.org/10.22331/q-2021-11-25-588}, title = {General {P}robabilistic {T}heories with a {G}leason-type {T}heorem}, author = {Wright, Victoria J and Weigert, Stefan}, journal = {{Quantum}}, issn = {2521-327X}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, volume = {5}, pages = {588}, month = nov, year = {2021} }`

- Tomasz Miller, Michał Eckstein, Paweł Horodecki, and Ryszard Horodecki. Generally covariant N -particle dynamics.
*Journal of Geometry and Physics*, 160:103990, feb 2021. doi:10.1016/j.geomphys.2020.103990

[BibTeX] [Download PDF]`@Article{miller_generally_2021, author = {Miller, Tomasz and Eckstein, Michał and Horodecki, Paweł and Horodecki, Ryszard}, journal = {Journal of {G}eometry and {P}hysics}, title = {Generally covariant {N} -particle dynamics}, year = {2021}, issn = {03930440}, month = feb, pages = {103990}, volume = {160}, doi = {10.1016/j.geomphys.2020.103990}, groups = {Pawel_H, Michal_H}, language = {en}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0393044020302539}, urldate = {2021-05-10}, }`

- Siddhartha Das, Stefan Bäuml, Marek Winczewski, and Karol Horodecki. Universal Limitations on Quantum Key Distribution over a Network.
*Physical Review X*, 11(4), oct 2021. doi:10.1103/physrevx.11.041016

[BibTeX] [Download PDF]`@article{Das_2021, doi = {10.1103/physrevx.11.041016}, url = {http://dx.doi.org/10.1103/physrevx.11.041016}, year = 2021, month = oct, publisher = {American Physical Society ({APS})}, volume = {11}, number = {4}, author = {Siddhartha Das and Stefan Bäuml and Marek Winczewski and Karol Horodecki}, title = {Universal Limitations on Quantum Key Distribution over a Network}, journal = {Physical Review X} }`

- B. Ahmadi, S. Salimi, and A. S. Khorashad. Irreversible work and Maxwell demon in terms of quantum thermodynamic force.
*Scientific Reports*, 11(1):2301, dec 2021. doi:10.1038/s41598-021-81737-z

[BibTeX] [Abstract] [Download PDF]

Abstract The second law of classical equilibrium thermodynamics, based on the positivity of entropy production, asserts that any process occurs only in a direction that some information may be lost (flow out of the system) due to the irreversibility inside the system. However, any thermodynamic system can exhibit fluctuations in which negative entropy production may be observed. In particular, in stochastic quantum processes due to quantum correlations and also memory effects we may see the reversal energy flow (heat flow from the cold system to the hot system) and the backflow of information into the system that leads to the negativity of the entropy production which is an apparent violation of the Second Law. In order to resolve this apparent violation, we will try to properly extend the Second Law to quantum processes by incorporating information explicitly into the Second Law. We will also provide a thermodynamic operational meaning for the flow and backflow of information. Finally, it is shown that negative and positive entropy production can be described by a quantum thermodynamic force.

`@Article{ahmadi_irreversible_2021, author = {Ahmadi, B. and Salimi, S. and Khorashad, A. S.}, journal = {Scientific {R}eports}, title = {Irreversible work and {Maxwell} demon in terms of quantum thermodynamic force}, year = {2021}, issn = {2045-2322}, month = dec, number = {1}, pages = {2301}, volume = {11}, abstract = {Abstract The second law of classical equilibrium thermodynamics, based on the positivity of entropy production, asserts that any process occurs only in a direction that some information may be lost (flow out of the system) due to the irreversibility inside the system. However, any thermodynamic system can exhibit fluctuations in which negative entropy production may be observed. In particular, in stochastic quantum processes due to quantum correlations and also memory effects we may see the reversal energy flow (heat flow from the cold system to the hot system) and the backflow of information into the system that leads to the negativity of the entropy production which is an apparent violation of the Second Law. In order to resolve this apparent violation, we will try to properly extend the Second Law to quantum processes by incorporating information explicitly into the Second Law. We will also provide a thermodynamic operational meaning for the flow and backflow of information. Finally, it is shown that negative and positive entropy production can be described by a quantum thermodynamic force.}, doi = {10.1038/s41598-021-81737-z}, language = {en}, url = {http://www.nature.com/articles/s41598-021-81737-z}, urldate = {2021-05-10}, }`

- Qihao Guo, Yuan-Yuan Zhao, Markus Grassl, Xinfang Nie, Guo-Yong Xiang, Tao Xin, Zhang-Qi Yin, and Bei Zeng. Testing a quantum error-correcting code on various platforms.
*Science Bulletin*, 66(1):29-35, jan 2021. doi:10.1016/j.scib.2020.07.033

[BibTeX] [Download PDF]`@Article{guo_testing_2021, author = {Guo, Qihao and Zhao, Yuan-Yuan and Grassl, Markus and Nie, Xinfang and Xiang, Guo-Yong and Xin, Tao and Yin, Zhang-Qi and Zeng, Bei}, journal = {Science {B}ulletin}, title = {Testing a quantum error-correcting code on various platforms}, year = {2021}, issn = {20959273}, month = jan, number = {1}, pages = {29--35}, volume = {66}, doi = {10.1016/j.scib.2020.07.033}, language = {en}, url = {https://linkinghub.elsevier.com/retrieve/pii/S2095927320305168}, urldate = {2021-05-10}, }`

- Piotr Mironowicz, Gustavo Cañas, Jaime Cariñe, Esteban S. Gómez, Johanna F. Barra, Adán Cabello, Guilherme B. Xavier, Gustavo Lima, and Marcin Pawłowski. Quantum randomness protected against detection loophole attacks.
*Quantum Information Processing*, 20(1):39, jan 2021. doi:10.1007/s11128-020-02948-3

[BibTeX] [Download PDF]`@Article{mironowicz_quantum_2021, author = {Mironowicz, Piotr and Cañas, Gustavo and Cariñe, Jaime and Gómez, Esteban S. and Barra, Johanna F. and Cabello, Adán and Xavier, Guilherme B. and Lima, Gustavo and Pawłowski, Marcin}, journal = {Quantum {I}nformation {P}rocessing}, title = {Quantum randomness protected against detection loophole attacks}, year = {2021}, issn = {1570-0755, 1573-1332}, month = jan, number = {1}, pages = {39}, volume = {20}, doi = {10.1007/s11128-020-02948-3}, language = {en}, url = {http://link.springer.com/10.1007/s11128-020-02948-3}, urldate = {2021-05-10}, }`

- Matthias Christandl, Roberto Ferrara, and Karol Horodecki. Upper Bounds on Device-Independent Quantum Key Distribution.
*Physical Review Letters*, 126(16):160501, apr 2021. doi:10.1103/PhysRevLett.126.160501

[BibTeX] [Download PDF]`@Article{christandl_upper_2021, author = {Christandl, Matthias and Ferrara, Roberto and Horodecki, Karol}, journal = {Physical {R}eview {L}etters}, title = {Upper {Bounds} on {Device}-{Independent} {Quantum} {Key} {Distribution}}, year = {2021}, issn = {0031-9007, 1079-7114}, month = apr, number = {16}, pages = {160501}, volume = {126}, doi = {10.1103/PhysRevLett.126.160501}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.160501}, urldate = {2021-05-10}, }`

- Robert Alicki, David Gelbwaser-Klimovsky, Alejandro Jenkins, and Elizabeth von Hauff. Dynamical theory for the battery’s electromotive force.
*Physical Chemistry Chemical Physics*, 23(15):9428-9439, 2021. doi:10.1039/D1CP00196E

[BibTeX] [Abstract] [Download PDF]

We propose a dynamical theory of how the chemical energy stored in a battery generates the electromotive force (emf). , We propose a dynamical theory of how the chemical energy stored in a battery generates the electromotive force (emf). In this picture, the battery’s half-cell acts as an engine, cyclically extracting work from its underlying chemical disequilibrium. We show that the double layer at the electrode–electrolyte interface can exhibit a rapid self-oscillation that pumps an electric current, thus accounting for the persistent conversion of chemical energy into electrical work equal to the emf times the separated charge. We suggest a connection between this mechanism and the slow self-oscillations observed in various electrochemical cells, including batteries, as well as the enhancement of the current observed when ultrasound is applied to the half-cell. Finally, we propose more direct experimental tests of the predictions of this dynamical theory.

`@Article{alicki_dynamical_2021, author = {Alicki, Robert and Gelbwaser-Klimovsky, David and Jenkins, Alejandro and von Hauff, Elizabeth}, journal = {Physical {C}hemistry {C}hemical {P}hysics}, title = {Dynamical theory for the battery's electromotive force}, year = {2021}, issn = {1463-9076, 1463-9084}, number = {15}, pages = {9428--9439}, volume = {23}, abstract = {We propose a dynamical theory of how the chemical energy stored in a battery generates the electromotive force (emf). , We propose a dynamical theory of how the chemical energy stored in a battery generates the electromotive force (emf). In this picture, the battery's half-cell acts as an engine, cyclically extracting work from its underlying chemical disequilibrium. We show that the double layer at the electrode–electrolyte interface can exhibit a rapid self-oscillation that pumps an electric current, thus accounting for the persistent conversion of chemical energy into electrical work equal to the emf times the separated charge. We suggest a connection between this mechanism and the slow self-oscillations observed in various electrochemical cells, including batteries, as well as the enhancement of the current observed when ultrasound is applied to the half-cell. Finally, we propose more direct experimental tests of the predictions of this dynamical theory.}, doi = {10.1039/D1CP00196E}, language = {en}, url = {http://xlink.rsc.org/?DOI=D1CP00196E}, urldate = {2021-05-10}, }`

- Marek Żukowski and Marcin Markiewicz. Physics and Metaphysics of Wigner’s Friends: Even Performed Premeasurements Have No Results.
*Physical Review Letters*, 126(13):130402, apr 2021. doi:10.1103/PhysRevLett.126.130402

[BibTeX] [Download PDF]`@Article{zukowski_physics_2021, author = {Żukowski, Marek and Markiewicz, Marcin}, journal = {Physical {R}eview {L}etters}, title = {Physics and {Metaphysics} of {Wigner}’s {Friends}: {Even} {Performed} {Premeasurements} {Have} {No} {Results}}, year = {2021}, issn = {0031-9007, 1079-7114}, month = apr, number = {13}, pages = {130402}, volume = {126}, doi = {10.1103/PhysRevLett.126.130402}, language = {en}, shorttitle = {Physics and {Metaphysics} of {Wigner}’s {Friends}}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.130402}, urldate = {2021-05-10}, }`

- John H. Selby, Carlo Maria Scandolo, and Bob Coecke. Reconstructing quantum theory from diagrammatic postulates.
*Quantum*, 5:445, apr 2021. doi:10.22331/q-2021-04-28-445

[BibTeX] [Abstract] [Download PDF]

A reconstruction of quantum theory refers to both a mathematical and a conceptual paradigm that allows one to derive the usual formulation of quantum theory from a set of primitive assumptions. The motivation for doing so is a discomfort with the usual formulation of quantum theory, a discomfort that started with its originator John von Neumann. We present a reconstruction of finite-dimensional quantum theory where all of the postulates are stated in diagrammatic terms, making them intuitive. Equivalently, they are stated in category-theoretic terms, making them mathematically appealing. Again equivalently, they are stated in process-theoretic terms, establishing that the conceptual backbone of quantum theory concerns the manner in which systems and processes compose. Aside from the diagrammatic form, the key novel aspect of this reconstruction is the introduction of a new postulate, symmetric purification. Unlike the ordinary purification postulate, symmetric purification applies equally well to classical theory as well as quantum theory. Therefore we first reconstruct the full process theoretic description of quantum theory, consisting of composite classical-quantum systems and their interactions, before restricting ourselves to just the ‘fully quantum’ systems as the final step. We propose two novel alternative manners of doing so, ‘no-leaking’ (roughly that information gain causes disturbance) and ‘purity of cups’ (roughly the existence of entangled states). Interestingly, these turn out to be equivalent in any process theory with cups & caps. Additionally, we show how the standard purification postulate can be seen as an immediate consequence of the symmetric purification postulate and purity of cups. Other tangential results concern the specific frameworks of generalised probabilistic theories (GPTs) and process theories (a.k.a. CQM). Firstly, we provide a diagrammatic presentation of GPTs, which, henceforth, can be subsumed under process theories. Secondly, we argue that the ‘sharp dagger’ is indeed the right choice of a dagger structure as this sharpness is vital to the reconstruction.

`@article{selby_reconstructing_2021, title = {Reconstructing quantum theory from diagrammatic postulates}, volume = {5}, issn = {2521-327X}, url = {https://quantum-journal.org/papers/q-2021-04-28-445/}, doi = {10.22331/q-2021-04-28-445}, abstract = {A reconstruction of quantum theory refers to both a mathematical and a conceptual paradigm that allows one to derive the usual formulation of quantum theory from a set of primitive assumptions. The motivation for doing so is a discomfort with the usual formulation of quantum theory, a discomfort that started with its originator John von Neumann. We present a reconstruction of finite-dimensional quantum theory where all of the postulates are stated in diagrammatic terms, making them intuitive. Equivalently, they are stated in category-theoretic terms, making them mathematically appealing. Again equivalently, they are stated in process-theoretic terms, establishing that the conceptual backbone of quantum theory concerns the manner in which systems and processes compose. Aside from the diagrammatic form, the key novel aspect of this reconstruction is the introduction of a new postulate, symmetric purification. Unlike the ordinary purification postulate, symmetric purification applies equally well to classical theory as well as quantum theory. Therefore we first reconstruct the full process theoretic description of quantum theory, consisting of composite classical-quantum systems and their interactions, before restricting ourselves to just the ‘fully quantum’ systems as the final step. We propose two novel alternative manners of doing so, ‘no-leaking’ (roughly that information gain causes disturbance) and ‘purity of cups’ (roughly the existence of entangled states). Interestingly, these turn out to be equivalent in any process theory with cups \& caps. Additionally, we show how the standard purification postulate can be seen as an immediate consequence of the symmetric purification postulate and purity of cups. Other tangential results concern the specific frameworks of generalised probabilistic theories (GPTs) and process theories (a.k.a. CQM). Firstly, we provide a diagrammatic presentation of GPTs, which, henceforth, can be subsumed under process theories. Secondly, we argue that the ‘sharp dagger’ is indeed the right choice of a dagger structure as this sharpness is vital to the reconstruction.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Selby, John H. and Scandolo, Carlo Maria and Coecke, Bob}, month = apr, year = {2021}, pages = {445}, }`

- H. S. Karthik, H. Akshata Shenoy, and Usha A. R. Devi. Leggett-Garg inequalities and temporal correlations for a qubit under PT -symmetric dynamics.
*Physical Review A*, 103(3):032420, mar 2021. doi:10.1103/PhysRevA.103.032420

[BibTeX] [Download PDF]`@Article{karthik_leggett-garg_2021, author = {Karthik, H. S. and Akshata Shenoy, H. and Devi, A. R. Usha}, journal = {Physical {R}eview {A}}, title = {Leggett-{Garg} inequalities and temporal correlations for a qubit under {PT} -symmetric dynamics}, year = {2021}, issn = {2469-9926, 2469-9934}, month = mar, number = {3}, pages = {032420}, volume = {103}, doi = {10.1103/PhysRevA.103.032420}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.103.032420}, urldate = {2021-05-10}, }`

- Nikolai Miklin and Michał Oszmaniec. A universal scheme for robust self-testing in the prepare-and-measure scenario.
*Quantum*, 5:424, apr 2021. doi:10.22331/q-2021-04-06-424

[BibTeX] [Abstract] [Download PDF]

We consider the problem of certification of arbitrary ensembles of pure states and projective measurements solely from the experimental statistics in the prepare-and-measure scenario assuming the upper bound on the dimension of the Hilbert space. To this aim, we propose a universal and intuitive scheme based on establishing perfect correlations between target states and suitably-chosen projective measurements. The method works in all finite dimensions and allows for robust certification of the overlaps between arbitrary preparation states and between the corresponding measurement operators. Finally, we prove that for qubits, our technique can be used to robustly self-test arbitrary configurations of pure quantum states and projective measurements. These results pave the way towards the practical application of the prepare-and-measure paradigm to certification of quantum devices.

`@article{miklin_universal_2021, title = {A universal scheme for robust self-testing in the prepare-and-measure scenario}, volume = {5}, issn = {2521-327X}, url = {https://quantum-journal.org/papers/q-2021-04-06-424/}, doi = {10.22331/q-2021-04-06-424}, abstract = {We consider the problem of certification of arbitrary ensembles of pure states and projective measurements solely from the experimental statistics in the prepare-and-measure scenario assuming the upper bound on the dimension of the Hilbert space. To this aim, we propose a universal and intuitive scheme based on establishing perfect correlations between target states and suitably-chosen projective measurements. The method works in all finite dimensions and allows for robust certification of the overlaps between arbitrary preparation states and between the corresponding measurement operators. Finally, we prove that for qubits, our technique can be used to robustly self-test arbitrary configurations of pure quantum states and projective measurements. These results pave the way towards the practical application of the prepare-and-measure paradigm to certification of quantum devices.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Miklin, Nikolai and Oszmaniec, Michał}, month = apr, year = {2021}, pages = {424}, }`

- David Schmid, John H. Selby, Elie Wolfe, Ravi Kunjwal, and Robert W. Spekkens. Characterization of Noncontextuality in the Framework of Generalized Probabilistic Theories.
*PRX Quantum*, 2(1):010331, feb 2021. doi:10.1103/PRXQuantum.2.010331

[BibTeX] [Download PDF]`@Article{schmid_characterization_2021, author = {Schmid, David and Selby, John H. and Wolfe, Elie and Kunjwal, Ravi and Spekkens, Robert W.}, journal = {P{RX} {Q}uantum}, title = {Characterization of {Noncontextuality} in the {Framework} of {Generalized} {Probabilistic} {Theories}}, year = {2021}, issn = {2691-3399}, month = feb, number = {1}, pages = {010331}, volume = {2}, doi = {10.1103/PRXQuantum.2.010331}, language = {en}, url = {https://link.aps.org/doi/10.1103/PRXQuantum.2.010331}, urldate = {2021-05-10}, }`

- Patryk Lipka-Bartosik, Paweł Mazurek, and Michał Horodecki. Second law of thermodynamics for batteries with vacuum state.
*Quantum*, 5:408, mar 2021. doi:10.22331/q-2021-03-10-408

[BibTeX] [Abstract] [Download PDF]

In stochastic thermodynamics work is a random variable whose average is bounded by the change in the free energy of the system. In most treatments, however, the work reservoir that absorbs this change is either tacitly assumed or modelled using unphysical systems with unbounded Hamiltonians (i.e. the ideal weight). In this work we describe the consequences of introducing the ground state of the battery and hence — of breaking its translational symmetry. The most striking consequence of this shift is the fact that the Jarzynski identity is replaced by a family of inequalities. Using these inequalities we obtain corrections to the second law of thermodynamics which vanish exponentially with the distance of the initial state of the battery to the bottom of its spectrum. Finally, we study an exemplary thermal operation which realizes the approximate Landauer erasure and demonstrate the consequences which arise when the ground state of the battery is explicitly introduced. In particular, we show that occupation of the vacuum state of any physical battery sets a lower bound on fluctuations of work, while batteries without vacuum state allow for fluctuation-free erasure.

`@Article{lipka-bartosik_second_2021, author = {Lipka-Bartosik, Patryk and Mazurek, Paweł and Horodecki, Michał}, journal = {Quantum}, title = {Second law of thermodynamics for batteries with vacuum state}, year = {2021}, issn = {2521-327X}, month = mar, pages = {408}, volume = {5}, abstract = {In stochastic thermodynamics work is a random variable whose average is bounded by the change in the free energy of the system. In most treatments, however, the work reservoir that absorbs this change is either tacitly assumed or modelled using unphysical systems with unbounded Hamiltonians (i.e. the ideal weight). In this work we describe the consequences of introducing the ground state of the battery and hence — of breaking its translational symmetry. The most striking consequence of this shift is the fact that the Jarzynski identity is replaced by a family of inequalities. Using these inequalities we obtain corrections to the second law of thermodynamics which vanish exponentially with the distance of the initial state of the battery to the bottom of its spectrum. Finally, we study an exemplary thermal operation which realizes the approximate Landauer erasure and demonstrate the consequences which arise when the ground state of the battery is explicitly introduced. In particular, we show that occupation of the vacuum state of any physical battery sets a lower bound on fluctuations of work, while batteries without vacuum state allow for fluctuation-free erasure.}, doi = {10.22331/q-2021-03-10-408}, groups = {Michal_H}, language = {en}, url = {https://quantum-journal.org/papers/q-2021-03-10-408/}, urldate = {2021-05-10}, }`

- Aaron Z. Goldberg, Pablo de la Hoz, Gunnar Björk, Andrei B. Klimov, Markus Grassl, Gerd Leuchs, and Luis L. Sánchez-Soto. Quantum concepts in optical polarization.
*Advances in Optics and Photonics*, 13(1):1, mar 2021. doi:10.1364/AOP.404175

[BibTeX] [Download PDF]`@Article{goldberg_quantum_2021, author = {Goldberg, Aaron Z. and de la Hoz, Pablo and Björk, Gunnar and Klimov, Andrei B. and Grassl, Markus and Leuchs, Gerd and Sánchez-Soto, Luis L.}, journal = {Advances in {O}ptics and {P}hotonics}, title = {Quantum concepts in optical polarization}, year = {2021}, issn = {1943-8206}, month = mar, number = {1}, pages = {1}, volume = {13}, doi = {10.1364/AOP.404175}, language = {en}, url = {https://www.osapublishing.org/abstract.cfm?URI=aop-13-1-1}, urldate = {2021-05-10}, }`

- Roope Uola, Tristan Kraft, Sébastien Designolle, Nikolai Miklin, Armin Tavakoli, Juha-Pekka Pellonpää, Otfried Gühne, and Nicolas Brunner. Quantum measurement incompatibility in subspaces.
*Physical Review A*, 103(2):022203, feb 2021. doi:10.1103/PhysRevA.103.022203

[BibTeX] [Download PDF]`@Article{uola_quantum_2021, author = {Uola, Roope and Kraft, Tristan and Designolle, Sébastien and Miklin, Nikolai and Tavakoli, Armin and Pellonpää, Juha-Pekka and Gühne, Otfried and Brunner, Nicolas}, journal = {Physical {R}eview {A}}, title = {Quantum measurement incompatibility in subspaces}, year = {2021}, issn = {2469-9926, 2469-9934}, month = feb, number = {2}, pages = {022203}, volume = {103}, doi = {10.1103/PhysRevA.103.022203}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.103.022203}, urldate = {2021-05-10}, }`

- Armin Tavakoli, Máté. Farkas, Denis Rosset, Jean-Daniel Bancal, and Jedrzej Kaniewski. Mutually unbiased bases and symmetric informationally complete measurements in Bell experiments.
*Science Advances*, 7(7):eabc3847, feb 2021. doi:10.1126/sciadv.abc3847

[BibTeX] [Abstract] [Download PDF]

Mutually unbiased bases (MUBs) and symmetric informationally complete projectors (SICs) are crucial to many conceptual and practical aspects of quantum theory. Here, we develop their role in quantum nonlocality by (i) introducing families of Bell inequalities that are maximally violated by d-dimensional MUBs and SICs, respectively, (ii) proving device-independent certification of natural operational notions of MUBs and SICs, and (iii) using MUBs and SICs to develop optimal-rate and nearly optimal-rate protocols for device-independent quantum key distribution and device-independent quantum random number generation, respectively. Moreover, we also present the first example of an extremal point of the quantum set of correlations that admits physically inequivalent quantum realizations. Our results elaborately demonstrate the foundational and practical relevance of the two most important discrete Hilbert space structures to the field of quantum nonlocality.

`@Article{tavakoli_mutually_2021, author = {Tavakoli, Armin and Farkas, Máté and Rosset, Denis and Bancal, Jean-Daniel and Kaniewski, Jedrzej}, journal = {Science {A}dvances}, title = {Mutually unbiased bases and symmetric informationally complete measurements in {Bell} experiments}, year = {2021}, issn = {2375-2548}, month = feb, number = {7}, pages = {eabc3847}, volume = {7}, abstract = {Mutually unbiased bases (MUBs) and symmetric informationally complete projectors (SICs) are crucial to many conceptual and practical aspects of quantum theory. Here, we develop their role in quantum nonlocality by (i) introducing families of Bell inequalities that are maximally violated by d-dimensional MUBs and SICs, respectively, (ii) proving device-independent certification of natural operational notions of MUBs and SICs, and (iii) using MUBs and SICs to develop optimal-rate and nearly optimal-rate protocols for device-independent quantum key distribution and device-independent quantum random number generation, respectively. Moreover, we also present the first example of an extremal point of the quantum set of correlations that admits physically inequivalent quantum realizations. Our results elaborately demonstrate the foundational and practical relevance of the two most important discrete Hilbert space structures to the field of quantum nonlocality.}, doi = {10.1126/sciadv.abc3847}, language = {en}, url = {https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abc3847}, urldate = {2021-05-10}, }`

- Máté. Farkas, Nayda Guerrero, Jaime Cariñe, Gustavo Cañas, and Gustavo Lima. Self-Testing Mutually Unbiased Bases in Higher Dimensions with Space-Division Multiplexing Optical Fiber Technology.
*Physical Review Applied*, 15(1):014028, jan 2021. doi:10.1103/PhysRevApplied.15.014028

[BibTeX] [Download PDF]`@Article{farkas_self-testing_2021, author = {Farkas, Máté and Guerrero, Nayda and Cariñe, Jaime and Cañas, Gustavo and Lima, Gustavo}, journal = {Physical {R}eview {A}pplied}, title = {Self-{Testing} {Mutually} {Unbiased} {Bases} in {Higher} {Dimensions} with {Space}-{Division} {Multiplexing} {Optical} {Fiber} {Technology}}, year = {2021}, issn = {2331-7019}, month = jan, number = {1}, pages = {014028}, volume = {15}, doi = {10.1103/PhysRevApplied.15.014028}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.15.014028}, urldate = {2021-05-10}, }`

- Konrad Schlichtholz, Bianka Woloncewicz, and Marek Żukowski. Nonclassicality of bright Greenberger-Horne-Zeilinger–like radiation of an optical parametric source.
*Physical Review A*, 103(4):042226, apr 2021. doi:10.1103/PhysRevA.103.042226

[BibTeX] [Download PDF]`@Article{schlichtholz_nonclassicality_2021, author = {Schlichtholz, Konrad and Woloncewicz, Bianka and Żukowski, Marek}, journal = {Physical {R}eview {A}}, title = {Nonclassicality of bright {Greenberger}-{Horne}-{Zeilinger}–like radiation of an optical parametric source}, year = {2021}, issn = {2469-9926, 2469-9934}, month = apr, number = {4}, pages = {042226}, volume = {103}, doi = {10.1103/PhysRevA.103.042226}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.103.042226}, urldate = {2021-07-28}, }`

- Roberto Salazar, Tanmoy Biswas, Jakub Czartowski, Karol Życzkowski, and Paweł Horodecki. Optimal allocation of quantum resources.
*Quantum*, 5:407, mar 2021. doi:10.22331/q-2021-03-10-407

[BibTeX] [Abstract] [Download PDF]

The optimal allocation of resources is a crucial task for their efficient use in a wide range of practical applications in science and engineering. This paper investigates the optimal allocation of resources in multipartite quantum systems. In particular, we show the relevance of proportional fairness and optimal reliability criteria for the application of quantum resources. Moreover, we present optimal allocation solutions for an arbitrary number of qudits using measurement incompatibility as an exemplary resource theory. Besides, we study the criterion of optimal equitability and demonstrate its relevance to scenarios involving several resource theories such as nonlocality vs local contextuality. Finally, we highlight the potential impact of our results for quantum networks and other multi-party quantum information processing, in particular to the future Quantum Internet.

`@Article{salazar_optimal_2021, author = {Salazar, Roberto and Biswas, Tanmoy and Czartowski, Jakub and Życzkowski, Karol and Horodecki, Paweł}, journal = {Quantum}, title = {Optimal allocation of quantum resources}, year = {2021}, issn = {2521-327X}, month = mar, pages = {407}, volume = {5}, abstract = {The optimal allocation of resources is a crucial task for their efficient use in a wide range of practical applications in science and engineering. This paper investigates the optimal allocation of resources in multipartite quantum systems. In particular, we show the relevance of proportional fairness and optimal reliability criteria for the application of quantum resources. Moreover, we present optimal allocation solutions for an arbitrary number of qudits using measurement incompatibility as an exemplary resource theory. Besides, we study the criterion of optimal equitability and demonstrate its relevance to scenarios involving several resource theories such as nonlocality vs local contextuality. Finally, we highlight the potential impact of our results for quantum networks and other multi-party quantum information processing, in particular to the future Quantum Internet.}, doi = {10.22331/q-2021-03-10-407}, groups = {Pawel_H}, language = {en}, url = {https://quantum-journal.org/papers/q-2021-03-10-407/}, urldate = {2021-07-28}, }`

- Chandan Datta, Tanmoy Biswas, Debashis Saha, and Remigiusz Augusiak. Perfect discrimination of quantum measurements using entangled systems.
*New Journal of Physics*, 23(4):043021, apr 2021. doi:10.1088/1367-2630/abecaf

[BibTeX] [Download PDF]`@Article{datta_perfect_2021, author = {Datta, Chandan and Biswas, Tanmoy and Saha, Debashis and Augusiak, Remigiusz}, journal = {New {J}ournal of {P}hysics}, title = {Perfect discrimination of quantum measurements using entangled systems}, year = {2021}, issn = {1367-2630}, month = apr, number = {4}, pages = {043021}, volume = {23}, doi = {10.1088/1367-2630/abecaf}, url = {https://iopscience.iop.org/article/10.1088/1367-2630/abecaf}, urldate = {2021-07-28}, }`

- R. Horodecki. Quantum Information.
*Acta Physica Polonica A*, 139(3):197-2018, mar 2021. doi:10.12693/APhysPolA.139.197

[BibTeX] [Download PDF]`@Article{horodecki_quantum_2021, author = {Horodecki, R.}, journal = {Acta {P}hysica {P}olonica {A}}, title = {Quantum {Information}}, year = {2021}, issn = {1898-794X, 0587-4246}, month = mar, number = {3}, pages = {197--2018}, volume = {139}, doi = {10.12693/APhysPolA.139.197}, url = {http://przyrbwn.icm.edu.pl/APP/PDF/139/app139z3p01.pdf}, urldate = {2021-07-28}, }`

- Marcin Wieśniak. Symmetrized persistency of Bell correlations for Dicke states and GHZ-based mixtures.
*Scientific Reports*, 11(1):14333, dec 2021. doi:10.1038/s41598-021-93786-5

[BibTeX] [Abstract] [Download PDF]

Abstract Quantum correlations, in particular those, which enable to violate a Bell inequality, open a way to advantage in certain communication tasks. However, the main difficulty in harnessing quantumness is its fragility to, e.g, noise or loss of particles. We study the persistency of Bell correlations of GHZ based mixtures and Dicke states. For the former, we consider quantum communication complexity reduction (QCCR) scheme, and propose new Bell inequalities (BIs), which can be used in that scheme for higher persistency in the limit of large number of particles N . In case of Dicke states, we show that persistency can reach 0.482 N , significantly more than reported in previous studies.

`@Article{wiesniak_symmetrized_2021, author = {Wieśniak, Marcin}, journal = {Scientific {R}eports}, title = {Symmetrized persistency of {Bell} correlations for {Dicke} states and {GHZ}-based mixtures}, year = {2021}, issn = {2045-2322}, month = dec, number = {1}, pages = {14333}, volume = {11}, abstract = {Abstract Quantum correlations, in particular those, which enable to violate a Bell inequality, open a way to advantage in certain communication tasks. However, the main difficulty in harnessing quantumness is its fragility to, e.g, noise or loss of particles. We study the persistency of Bell correlations of GHZ based mixtures and Dicke states. For the former, we consider quantum communication complexity reduction (QCCR) scheme, and propose new Bell inequalities (BIs), which can be used in that scheme for higher persistency in the limit of large number of particles N . In case of Dicke states, we show that persistency can reach 0.482 N , significantly more than reported in previous studies.}, doi = {10.1038/s41598-021-93786-5}, language = {en}, url = {http://www.nature.com/articles/s41598-021-93786-5}, urldate = {2021-07-28}, }`

- K. Anjali, Akshata Shenoy Hejamadi, H. S. Karthik, S. Sahu, Sudha, and Usha A. R. Devi. Characterizing nonlocality of pure symmetric three-qubit states.
*Quantum Information Processing*, 20(5):187, may 2021. doi:10.1007/s11128-021-03124-x

[BibTeX] [Download PDF]`@Article{anjali_characterizing_2021, author = {Anjali, K. and Hejamadi, Akshata Shenoy and Karthik, H. S. and Sahu, S. and {Sudha} and Devi, A. R. Usha}, journal = {Quantum {I}nformation {P}rocessing}, title = {Characterizing nonlocality of pure symmetric three-qubit states}, year = {2021}, issn = {1570-0755, 1573-1332}, month = may, number = {5}, pages = {187}, volume = {20}, doi = {10.1007/s11128-021-03124-x}, language = {en}, url = {https://link.springer.com/10.1007/s11128-021-03124-x}, urldate = {2021-07-28}, }`

- Michał Banacki, Ricard Ravell Rodríguez, and Paweł Horodecki. On the edge of the set of no-signaling assemblages.
*Physical Review A*, 103(5):052434, may 2021. arXiv: 2008.12325 doi:10.1103/PhysRevA.103.052434

[BibTeX] [Abstract] [Download PDF]

Following recent advancements, we consider a scenario of multipartite postquantum steering and general no-signaling assemblages. We introduce the notion of the edge of the set of no-signaling assemblages and we present its characterization. Next, we use this concept to construct witnesses for no-signaling assemblages without an LHS model. Finally, in the simplest nontrivial case of steering with two untrusted subsystems, we discuss the possibility of quantum realization of assemblages on the edge. In particular, for three-qubit states, we obtain a no-go type result, which states that it is impossible to produce assemblage on the edge using measurements described by POVMs as long as the rank of a given state is greater than or equal to 3.

`@Article{banacki_edge_2021, author = {Banacki, Michał and Rodríguez, Ricard Ravell and Horodecki, Paweł}, journal = {Physical {R}eview {A}}, title = {On the edge of the set of no-signaling assemblages}, year = {2021}, issn = {2469-9926, 2469-9934}, month = may, note = {arXiv: 2008.12325}, number = {5}, pages = {052434}, volume = {103}, abstract = {Following recent advancements, we consider a scenario of multipartite postquantum steering and general no-signaling assemblages. We introduce the notion of the edge of the set of no-signaling assemblages and we present its characterization. Next, we use this concept to construct witnesses for no-signaling assemblages without an LHS model. Finally, in the simplest nontrivial case of steering with two untrusted subsystems, we discuss the possibility of quantum realization of assemblages on the edge. In particular, for three-qubit states, we obtain a no-go type result, which states that it is impossible to produce assemblage on the edge using measurements described by POVMs as long as the rank of a given state is greater than or equal to 3.}, doi = {10.1103/PhysRevA.103.052434}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2008.12325}, urldate = {2021-07-28}, }`

- Stefano Cusumano and Łukasz Rudnicki. Comment on “Fluctuations in Extractable Work Bound the Charging Power of Quantum Batteries”.
*Physical Review Letters*, 127(2):028901, jul 2021. arXiv: 2102.05627 doi:10.1103/PhysRevLett.127.028901

[BibTeX] [Abstract] [Download PDF]

In the abstract of\textasciitilde[Phys. Rev. Lett. \\textbackslashbf 125\, 040601 (2020)] one can read that: […]\\textbackslashit to have a nonzero rate of change of the extractable work, the state \$\textbackslashrho\_\textbackslashmathcal\W\\$ of the battery cannot be an eigenstate of a “free energy operator”, defined by \$\textbackslashmathcal\F\=H\_\textbackslashmathcal\W\+\textbackslashbeta\textasciicircum\-1\\textbackslashlog \textbackslashrho\_\textbackslashmathcal\W\\$, where \$H\_\textbackslashmathcal\W\\$ is the Hamiltonian of the battery and \$\textbackslashbeta\$ is the inverse temperature\ […]. Contrarily to what is presented below Eq.\textasciitilde(17) of the paper, we observe that the above conclusion does not hold when the battery is subject to nonunitary dynamics.

`@Article{cusumano_comment_2021, author = {Cusumano, Stefano and Rudnicki, Łukasz}, journal = {Physical {R}eview {L}etters}, title = {Comment on "{Fluctuations} in {Extractable} {Work} {Bound} the {Charging} {Power} of {Quantum} {Batteries}"}, year = {2021}, issn = {0031-9007, 1079-7114}, month = jul, note = {arXiv: 2102.05627}, number = {2}, pages = {028901}, volume = {127}, abstract = {In the abstract of{\textasciitilde}[Phys. Rev. Lett. \{{\textbackslash}bf 125\}, 040601 (2020)] one can read that: [...]\{{\textbackslash}it to have a nonzero rate of change of the extractable work, the state \${\textbackslash}rho\_{\textbackslash}mathcal\{W\}\$ of the battery cannot be an eigenstate of a "free energy operator", defined by \${\textbackslash}mathcal\{F\}=H\_{\textbackslash}mathcal\{W\}+{\textbackslash}beta{\textasciicircum}\{-1\}{\textbackslash}log {\textbackslash}rho\_{\textbackslash}mathcal\{W\}\$, where \$H\_{\textbackslash}mathcal\{W\}\$ is the Hamiltonian of the battery and \${\textbackslash}beta\$ is the inverse temperature\} [...]. Contrarily to what is presented below Eq.{\textasciitilde}(17) of the paper, we observe that the above conclusion does not hold when the battery is subject to nonunitary dynamics.}, doi = {10.1103/PhysRevLett.127.028901}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2102.05627}, urldate = {2021-07-28}, note = {acknowledgment to ICTQT IRAP project included} }`

- Nikolai Miklin and Marcin Pawłowski. Information Causality without concatenation.
*Physical Review Letters*, 126(22):220403, jun 2021. arXiv: 2101.12710 doi:10.1103/PhysRevLett.126.220403

[BibTeX] [Abstract] [Download PDF]

Information Causality is a physical principle which states that the amount of randomly accessible data over a classical communication channel cannot exceed its capacity, even if the sender and the receiver have access to a source of nonlocal correlations. This principle can be used to bound the nonlocality of quantum mechanics without resorting to its full formalism, with a notable example of reproducing the Tsirelson’s bound of the Clauser-Horne-Shimony-Holt inequality. Despite being promising, the latter result found little generalization to other Bell inequalities because of the limitations imposed by the process of concatenation, in which several nonsignaling resources are put together to produce tighter bounds. In this work, we show that concatenation can be successfully replaced by limits on the communication channel capacity. It allows us to re-derive and, in some cases, significantly improve all the previously known results in a simpler manner and apply the Information Causality principle to previously unapproachable Bell scenarios.

`@Article{miklin_information_2021, author = {Miklin, Nikolai and Pawłowski, Marcin}, journal = {Physical {R}eview {L}etters}, title = {Information {Causality} without concatenation}, year = {2021}, issn = {0031-9007, 1079-7114}, month = jun, note = {arXiv: 2101.12710}, number = {22}, pages = {220403}, volume = {126}, abstract = {Information Causality is a physical principle which states that the amount of randomly accessible data over a classical communication channel cannot exceed its capacity, even if the sender and the receiver have access to a source of nonlocal correlations. This principle can be used to bound the nonlocality of quantum mechanics without resorting to its full formalism, with a notable example of reproducing the Tsirelson's bound of the Clauser-Horne-Shimony-Holt inequality. Despite being promising, the latter result found little generalization to other Bell inequalities because of the limitations imposed by the process of concatenation, in which several nonsignaling resources are put together to produce tighter bounds. In this work, we show that concatenation can be successfully replaced by limits on the communication channel capacity. It allows us to re-derive and, in some cases, significantly improve all the previously known results in a simpler manner and apply the Information Causality principle to previously unapproachable Bell scenarios.}, doi = {10.1103/PhysRevLett.126.220403}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2101.12710}, urldate = {2021-07-28}, }`

- Shin-Liang Chen, Nikolai Miklin, Costantino Budroni, and Yueh-Nan Chen. Device-independent quantification of measurement incompatibility.
*Physical Review Research*, 3(2):023143, may 2021. arXiv: 2010.08456 doi:10.1103/PhysRevResearch.3.023143

[BibTeX] [Abstract] [Download PDF]

Incompatible measurements, i.e., measurements that cannot be simultaneously performed, are necessary to observe nonlocal correlations. It is natural to ask, e.g., how incompatible the measurements have to be to achieve a certain violation of a Bell inequality. In this work, we provide the direct link between Bell nonlocality and the quantification of measurement incompatibility. This includes quantifiers for both incompatible and genuine-multipartite incompatible measurements. Our method straightforwardly generalizes to include constraints on the system’s dimension (semi-device-independent approach) and on projective measurements, providing improved bounds on incompatibility quantifiers, and to include the prepare-and-measure scenario.

`@Article{chen_device-independent_2021, author = {Chen, Shin-Liang and Miklin, Nikolai and Budroni, Costantino and Chen, Yueh-Nan}, journal = {Physical {R}eview {R}esearch}, title = {Device-independent quantification of measurement incompatibility}, year = {2021}, issn = {2643-1564}, month = may, note = {arXiv: 2010.08456}, number = {2}, pages = {023143}, volume = {3}, abstract = {Incompatible measurements, i.e., measurements that cannot be simultaneously performed, are necessary to observe nonlocal correlations. It is natural to ask, e.g., how incompatible the measurements have to be to achieve a certain violation of a Bell inequality. In this work, we provide the direct link between Bell nonlocality and the quantification of measurement incompatibility. This includes quantifiers for both incompatible and genuine-multipartite incompatible measurements. Our method straightforwardly generalizes to include constraints on the system's dimension (semi-device-independent approach) and on projective measurements, providing improved bounds on incompatibility quantifiers, and to include the prepare-and-measure scenario.}, doi = {10.1103/PhysRevResearch.3.023143}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2010.08456}, urldate = {2021-07-28}, }`

- Markus Grassl. Entanglement-Assisted Quantum Communication Beating the Quantum Singleton Bound.
*Physical Review A*, 103(2):L020601, feb 2021. arXiv: 2007.01249 doi:10.1103/PhysRevA.103.L020601

[BibTeX] [Abstract] [Download PDF]

Brun, Devetak, and Hsieh [Science 314, 436 (2006)] demonstrated that pre-shared entanglement between sender and receiver enables quantum communication protocols that have better parameters than schemes without the assistance of entanglement. Subsequently, the same authors derived a version of the so-called quantum Singleton bound that relates the parameters of the entanglement-assisted quantum-error correcting codes proposed by them. We present a new entanglement-assisted quantum communication scheme with parameters violating this bound in certain ranges.

`@Article{grassl_entanglement-assisted_2021, author = {Grassl, Markus}, journal = {Physical {R}eview {A}}, title = {Entanglement-{Assisted} {Quantum} {Communication} {Beating} the {Quantum} {Singleton} {Bound}}, year = {2021}, issn = {2469-9926, 2469-9934}, month = feb, note = {arXiv: 2007.01249}, number = {2}, pages = {L020601}, volume = {103}, abstract = {Brun, Devetak, and Hsieh [Science 314, 436 (2006)] demonstrated that pre-shared entanglement between sender and receiver enables quantum communication protocols that have better parameters than schemes without the assistance of entanglement. Subsequently, the same authors derived a version of the so-called quantum Singleton bound that relates the parameters of the entanglement-assisted quantum-error correcting codes proposed by them. We present a new entanglement-assisted quantum communication scheme with parameters violating this bound in certain ranges.}, doi = {10.1103/PhysRevA.103.L020601}, keywords = {Quantum Physics, Computer Science - Information Theory}, url = {http://arxiv.org/abs/2007.01249}, urldate = {2021-07-28}, }`

- Wooyeong Song, Youngrong Lim, Hyukjoon Kwon, Gerardo Adesso, Marcin Wieśniak, Marcin Pawłowski, Jaewan Kim, and Jeongho Bang. Quantum secure learning with classical samples.
*Physical Review A*, 103(4):042409, apr 2021. arXiv: 1912.10594 doi:10.1103/PhysRevA.103.042409

[BibTeX] [Abstract] [Download PDF]

Studies addressing the question “Can a learner complete the learning securely?” have recently been spurred from the standpoints of fundamental theory and potential applications. In the relevant context of this question, we present a classical-quantum hybrid sampling protocol and define a security condition that allows only legitimate learners to prepare a finite set of samples that guarantees the success of the learning; the security condition excludes intruders. We do this by combining our security concept with the bound of the so-called probably approximately correct (PAC) learning. We show that while the lower bound on the learning samples guarantees PAC learning, an upper bound can be derived to rule out adversarial learners. Such a secure learning condition is appealing, because it is defined only by the size of samples required for the successful learning and is independent of the algorithm employed. Notably, the security stems from the fundamental quantum no-broadcasting principle. No such condition can thus occur in any classical regime, where learning samples can be copied. Owing to the hybrid architecture, our scheme also offers a practical advantage for implementation in noisy intermediate-scale quantum devices.

`@Article{song_quantum_2021, author = {Song, Wooyeong and Lim, Youngrong and Kwon, Hyukjoon and Adesso, Gerardo and Wieśniak, Marcin and Pawłowski, Marcin and Kim, Jaewan and Bang, Jeongho}, journal = {Physical {R}eview {A}}, title = {Quantum secure learning with classical samples}, year = {2021}, issn = {2469-9926, 2469-9934}, month = apr, note = {arXiv: 1912.10594}, number = {4}, pages = {042409}, volume = {103}, abstract = {Studies addressing the question "Can a learner complete the learning securely?" have recently been spurred from the standpoints of fundamental theory and potential applications. In the relevant context of this question, we present a classical-quantum hybrid sampling protocol and define a security condition that allows only legitimate learners to prepare a finite set of samples that guarantees the success of the learning; the security condition excludes intruders. We do this by combining our security concept with the bound of the so-called probably approximately correct (PAC) learning. We show that while the lower bound on the learning samples guarantees PAC learning, an upper bound can be derived to rule out adversarial learners. Such a secure learning condition is appealing, because it is defined only by the size of samples required for the successful learning and is independent of the algorithm employed. Notably, the security stems from the fundamental quantum no-broadcasting principle. No such condition can thus occur in any classical regime, where learning samples can be copied. Owing to the hybrid architecture, our scheme also offers a practical advantage for implementation in noisy intermediate-scale quantum devices.}, doi = {10.1103/PhysRevA.103.042409}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/1912.10594}, urldate = {2021-07-28}, }`

- Marcin Markiewicz, Marcin Karczewski, and Pawel Kurzynski. Borromean states in discrete-time quantum walks.
*Quantum*, 5:523, aug 2021. doi:10.22331/q-2021-08-16-523

[BibTeX] [Download PDF]`@Article{Markiewicz2021borromeanstatesin, author = {Markiewicz, Marcin and Karczewski, Marcin and Kurzynski, Pawel}, journal = {{Quantum}}, title = {Borromean states in discrete-time quantum walks}, year = {2021}, issn = {2521-327X}, month = aug, pages = {523}, volume = {5}, doi = {10.22331/q-2021-08-16-523}, publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}}, url = {https://doi.org/10.22331/q-2021-08-16-523}, }`

- Robert Alicki, David Gelbwaser-Klimovsky, and Alejandro Jenkins. The Problem of Engines in Statistical Physics.
*Entropy*, 23(8), 2021. doi:10.3390/e23081095

[BibTeX] [Abstract] [Download PDF]

Engines are open systems that can generate work cyclically at the expense of an external disequilibrium. They are ubiquitous in nature and technology, but the course of mathematical physics over the last 300 years has tended to make their dynamics in time a theoretical blind spot. This has hampered the usefulness of statistical mechanics applied to active systems, including living matter. We argue that recent advances in the theory of open quantum systems, coupled with renewed interest in understanding how active forces result from positive feedback between different macroscopic degrees of freedom in the presence of dissipation, point to a more realistic description of autonomous engines. We propose a general conceptualization of an engine that helps clarify the distinction between its heat and work outputs. Based on this, we show how the external loading force and the thermal noise may be incorporated into the relevant equations of motion. This modifies the usual Fokker–Planck and Langevin equations, offering a thermodynamically complete formulation of the irreversible dynamics of simple oscillating and rotating engines.

`@Article{AlickiAugust2021, author = {Alicki, Robert and Gelbwaser-Klimovsky, David and Jenkins, Alejandro}, journal = {Entropy}, title = {The Problem of Engines in Statistical Physics}, year = {2021}, issn = {1099-4300}, number = {8}, volume = {23}, abstract = {Engines are open systems that can generate work cyclically at the expense of an external disequilibrium. They are ubiquitous in nature and technology, but the course of mathematical physics over the last 300 years has tended to make their dynamics in time a theoretical blind spot. This has hampered the usefulness of statistical mechanics applied to active systems, including living matter. We argue that recent advances in the theory of open quantum systems, coupled with renewed interest in understanding how active forces result from positive feedback between different macroscopic degrees of freedom in the presence of dissipation, point to a more realistic description of autonomous engines. We propose a general conceptualization of an engine that helps clarify the distinction between its heat and work outputs. Based on this, we show how the external loading force and the thermal noise may be incorporated into the relevant equations of motion. This modifies the usual Fokker–Planck and Langevin equations, offering a thermodynamically complete formulation of the irreversible dynamics of simple oscillating and rotating engines.}, article-number = {1095}, doi = {10.3390/e23081095}, pubmedid = {34441235}, url = {https://www.mdpi.com/1099-4300/23/8/1095}, }`

- Maciej Stankiewicz, Karol Horodecki, Omer Sakarya, and Danuta Makowiec. Private Weakly-Random Sequences from Human Heart Rate for Quantum Amplification.
*Entropy*, 23(9):1182, sep 2021. doi:10.3390/e23091182

[BibTeX] [Abstract] [Download PDF]

We investigate whether the heart rate can be treated as a semi-random source with the aim of amplification by quantum devices. We use a semi-random source model called $\epsilon$-Santha-Vazirani source, which can be amplified via quantum protocols to obtain fully private random sequence. We analyze time intervals between consecutive heartbeats obtained from Holter electrocardiogram (ECG) recordings of people of different sex and age. We propose several transformations of the original time series into binary sequences. We have performed different statistical randomness tests and estimated quality parameters. We find that the heart can be treated as good enough, and private by its nature, source of randomness, that every human possesses. As such, in principle it can be used as input to quantum device-independent randomness amplification protocols. The properly interpreted $\epsilon$ parameter can potentially serve as a new characteristic of the human’s heart from the perspective of medicine.

`@Article{Stankiewicz2021, author = {Stankiewicz, Maciej and Horodecki, Karol and Sakarya, Omer and Makowiec, Danuta}, journal = {Entropy}, title = {Private {W}eakly-{R}andom {S}equences from {H}uman {H}eart {R}ate for {Q}uantum {A}mplification}, year = {2021}, month = sep, number = {9}, pages = {1182}, volume = {23}, abstract = {We investigate whether the heart rate can be treated as a semi-random source with the aim of amplification by quantum devices. We use a semi-random source model called $\epsilon$-Santha-Vazirani source, which can be amplified via quantum protocols to obtain fully private random sequence. We analyze time intervals between consecutive heartbeats obtained from Holter electrocardiogram (ECG) recordings of people of different sex and age. We propose several transformations of the original time series into binary sequences. We have performed different statistical randomness tests and estimated quality parameters. We find that the heart can be treated as good enough, and private by its nature, source of randomness, that every human possesses. As such, in principle it can be used as input to quantum device-independent randomness amplification protocols. The properly interpreted $\epsilon$ parameter can potentially serve as a new characteristic of the human's heart from the perspective of medicine.}, archiveprefix = {arXiv}, doi = {10.3390/e23091182}, eprint = {2107.14630}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021Entrp..23.1182S}, }`

- Anubhav Chaturvedi, Máté. Farkas, and Victoria J. Wright. Characterising and bounding the set of quantum behaviours in contextuality scenarios.
*Quantum*, 5:484, 06 2021. doi:10.22331/q-2021-06-29-484

[BibTeX] [Abstract] [Download PDF]

The predictions of quantum theory resist generalised noncontextual explanations. In addition to the foundational relevance of this fact, the particular extent to which quantum theory violates noncontextuality limits available quantum advantage in communication and information processing. In the first part of this work, we formally define contextuality scenarios via prepare-and-measure experiments, along with the polytope of general contextual behaviours containing the set of quantum contextual behaviours. This framework allows us to recover several properties of set of quantum behaviours in these scenarios, including contextuality scenarios and associated noncontextuality inequalities that require for their violation the individual quantum preparation and measurement procedures to be mixed states and unsharp measurements. With the framework in place, we formulate novel semidefinite programming relaxations for bounding these sets of quantum contextual behaviours. Most significantly, to circumvent the inadequacy of pure states and projective measurements in contextuality scenarios, we present a novel unitary operator based semidefinite relaxation technique. We demonstrate the efficacy of these relaxations by obtaining tight upper bounds on the quantum violation of several noncontextuality inequalities and identifying novel maximally contextual quantum strategies. To further illustrate the versatility of these relaxations, we demonstrate $\textitmonogamy of preparation contextuality$ in a tripartite setting, and present a secure semi-device independent quantum key distribution scheme powered by quantum advantage in parity oblivious random access codes.

`@Article{Chaturvedi2021, author = {Anubhav Chaturvedi and Máté Farkas and Victoria J Wright}, journal = {Quantum}, title = {Characterising and bounding the set of quantum behaviours in contextuality scenarios}, year = {2021}, issn = {2521-327X}, month = {06}, pages = {484}, volume = {5}, abstract = {The predictions of quantum theory resist generalised noncontextual explanations. In addition to the foundational relevance of this fact, the particular extent to which quantum theory violates noncontextuality limits available quantum advantage in communication and information processing. In the first part of this work, we formally define contextuality scenarios via prepare-and-measure experiments, along with the polytope of general contextual behaviours containing the set of quantum contextual behaviours. This framework allows us to recover several properties of set of quantum behaviours in these scenarios, including contextuality scenarios and associated noncontextuality inequalities that require for their violation the individual quantum preparation and measurement procedures to be mixed states and unsharp measurements. With the framework in place, we formulate novel semidefinite programming relaxations for bounding these sets of quantum contextual behaviours. Most significantly, to circumvent the inadequacy of pure states and projective measurements in contextuality scenarios, we present a novel unitary operator based semidefinite relaxation technique. We demonstrate the efficacy of these relaxations by obtaining tight upper bounds on the quantum violation of several noncontextuality inequalities and identifying novel maximally contextual quantum strategies. To further illustrate the versatility of these relaxations, we demonstrate $\textit{monogamy of preparation contextuality}$ in a tripartite setting, and present a secure semi-device independent quantum key distribution scheme powered by quantum advantage in parity oblivious random access codes.}, doi = {10.22331/q-2021-06-29-484}, groups = {Sainz}, publisher = {Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften}, url = {https://quantum-journal.org/papers/q-2021-06-29-484/pdf/}, }`

- Artur Barasiński, Antonín Černoch, Wiesław Laskowski, Karel Lemr, Tamás Vértesi, and Jan Soubusta. Experimentally friendly approach towards nonlocal correlations in multisetting N-partite Bell scenarios.
*Quantum*, 5:430, apr 2021. doi:10.22331/q-2021-04-14-430

[BibTeX] [Abstract] [Download PDF]

In this work, we study a recently proposed operational measure of nonlocality by Fonseca and Parisio [Phys. Rev. A 92, 030101(R) (2015)] which describes the probability of violation of local realism under randomly sampled observables, and the strength of such violation as described by resistance to white noise admixture. While our knowledge concerning these quantities is well established from a theoretical point of view, the experimental counterpart is a considerably harder task and very little has been done in this field. It is caused by the lack of complete knowledge about the facets of the local polytope required for the analysis. In this paper, we propose a simple procedure towards experimentally determining both quantities for N -qubit pure states, based on the incomplete set of tight Bell inequalities. We show that the imprecision arising from this approach is of similar magnitude as the potential measurement errors. We also show that even with both a randomly chosen N -qubit pure state and randomly chosen measurement bases, a violation of local realism can be detected experimentally almost 100 \% of the time. Among other applications, our work provides a feasible alternative for the witnessing of genuine multipartite entanglement without aligned reference frames.

`@Article{Barasinski2021, author = {Barasiński, Artur and Černoch, Antonín and Laskowski, Wiesław and Lemr, Karel and Vértesi, Tamás and Soubusta, Jan}, journal = {Quantum}, title = {Experimentally friendly approach towards nonlocal correlations in multisetting {N}-partite {Bell} scenarios}, year = {2021}, issn = {2521-327X}, month = apr, pages = {430}, volume = {5}, abstract = {In this work, we study a recently proposed operational measure of nonlocality by Fonseca and Parisio [Phys. Rev. A 92, 030101(R) (2015)] which describes the probability of violation of local realism under randomly sampled observables, and the strength of such violation as described by resistance to white noise admixture. While our knowledge concerning these quantities is well established from a theoretical point of view, the experimental counterpart is a considerably harder task and very little has been done in this field. It is caused by the lack of complete knowledge about the facets of the local polytope required for the analysis. In this paper, we propose a simple procedure towards experimentally determining both quantities for N -qubit pure states, based on the incomplete set of tight Bell inequalities. We show that the imprecision arising from this approach is of similar magnitude as the potential measurement errors. We also show that even with both a randomly chosen N -qubit pure state and randomly chosen measurement bases, a violation of local realism can be detected experimentally almost 100 \% of the time. Among other applications, our work provides a feasible alternative for the witnessing of genuine multipartite entanglement without aligned reference frames.}, doi = {10.22331/q-2021-04-14-430}, language = {en}, url = {https://quantum-journal.org/papers/q-2021-04-14-430/}, urldate = {2021-10-11}, }`

- Pawel Blasiak, Ewa Borsuk, Marcin Markiewicz, and Yong-Su Kim. Efficient linear-optical generation of a multipartite W state.
*Physical Review A*, 104(2):023701, aug 2021. doi:10.1103/PhysRevA.104.023701

[BibTeX] [Download PDF]`@Article{Blasiak2021, author = {Blasiak, Pawel and Borsuk, Ewa and Markiewicz, Marcin and Kim, Yong-Su}, journal = {Physical {R}eview {A}}, title = {Efficient linear-optical generation of a multipartite {W} state}, year = {2021}, issn = {2469-9926, 2469-9934}, month = aug, number = {2}, pages = {023701}, volume = {104}, doi = {10.1103/PhysRevA.104.023701}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.104.023701}, urldate = {2021-10-11}, }`

- Erik Aurell, Michał Eckstein, and Paweł Horodecki. Quantum Black Holes as Solvents.
*Foundations of Physics*, 51(2):54, apr 2021. doi:10.1007/s10701-021-00456-7

[BibTeX] [Abstract] [Download PDF]

Abstract Almost all of the entropy in the universe is in the form of Bekenstein–Hawking (BH) entropy of super-massive black holes. This entropy, if it satisfies Boltzmann’s equation \$\$S=\textbackslashlog \textbackslashmathcal\N\\$\$ S = log N , hence represents almost all the accessible phase space of the Universe, somehow associated to objects which themselves fill out a very small fraction of ordinary three-dimensional space. Although time scales are very long, it is believed that black holes will eventually evaporate by emitting Hawking radiation, which is thermal when counted mode by mode. A pure quantum state collapsing to a black hole will hence eventually re-emerge as a state with strictly positive entropy, which constitutes the famous black hole information paradox. Expanding on a remark by Hawking we posit that BH entropy is a thermodynamic entropy, which must be distinguished from information-theoretic entropy. The paradox can then be explained by information return in Hawking radiation. The novel perspective advanced here is that if BH entropy counts the number of accessible physical states in a quantum black hole, then the paradox can be seen as an instance of the fundamental problem of statistical mechanics. We suggest a specific analogy to the increase of the entropy in a solvation process. We further show that the huge phase volume ( \$\$\textbackslashmathcal\N\\$\$ N ), which must be made available to the universe in a gravitational collapse, cannot originate from the entanglement between ordinary matter and/or radiation inside and outside the black hole. We argue that, instead, the quantum degrees of freedom of the gravitational field must get activated near the singularity, resulting in a final state of the ‘entangled entanglement’ form involving both matter and gravity.

`@Article{Aurell2021, author = {Aurell, Erik and Eckstein, Michał and Horodecki, Paweł}, journal = {Foundations of {P}hysics}, title = {Quantum {Black} {Holes} as {Solvents}}, year = {2021}, issn = {0015-9018, 1572-9516}, month = apr, number = {2}, pages = {54}, volume = {51}, abstract = {Abstract Almost all of the entropy in the universe is in the form of Bekenstein–Hawking (BH) entropy of super-massive black holes. This entropy, if it satisfies Boltzmann’s equation \$\$S={\textbackslash}log {\textbackslash}mathcal\{N\}\$\$ S = log N , hence represents almost all the accessible phase space of the Universe, somehow associated to objects which themselves fill out a very small fraction of ordinary three-dimensional space. Although time scales are very long, it is believed that black holes will eventually evaporate by emitting Hawking radiation, which is thermal when counted mode by mode. A pure quantum state collapsing to a black hole will hence eventually re-emerge as a state with strictly positive entropy, which constitutes the famous black hole information paradox. Expanding on a remark by Hawking we posit that BH entropy is a thermodynamic entropy, which must be distinguished from information-theoretic entropy. The paradox can then be explained by information return in Hawking radiation. The novel perspective advanced here is that if BH entropy counts the number of accessible physical states in a quantum black hole, then the paradox can be seen as an instance of the fundamental problem of statistical mechanics. We suggest a specific analogy to the increase of the entropy in a solvation process. We further show that the huge phase volume ( \$\${\textbackslash}mathcal\{N\}\$\$ N ), which must be made available to the universe in a gravitational collapse, cannot originate from the entanglement between ordinary matter and/or radiation inside and outside the black hole. We argue that, instead, the quantum degrees of freedom of the gravitational field must get activated near the singularity, resulting in a final state of the ‘entangled entanglement’ form involving both matter and gravity.}, doi = {10.1007/s10701-021-00456-7}, groups = {Pawel_H}, language = {en}, url = {https://link.springer.com/10.1007/s10701-021-00456-7}, urldate = {2021-10-11}, }`

- Robert Alicki, David Gelbwaser-Klimovsky, and Alejandro Jenkins. Leaking elastic capacitor as model for active matter.
*Physical Review E*, 103(5):052131, may 2021. doi:10.1103/PhysRevE.103.052131

[BibTeX] [Abstract] [Download PDF]

We introduce the “leaking elastic capacitor” (LEC) model, a nonconservative dynamical system that combines simple electrical and mechanical degrees of freedom. We show that an LEC connected to an external voltage source can be destabilized (Hopf bifurcation) due to positive feedback between the mechanical separation of the plates and their electrical charging. Numerical simulation finds regimes in which the LEC exhibits a limit cycle (regular self-oscillation) or strange attractors (chaos). The LEC acts as an autonomous engine, cyclically performing work at the expense of the constant voltage source. We show that this mechanical work can be used to pump current, generating an electromotive force without any time-varying magnetic flux and in a thermodynamically irreversible way. We consider how this mechanism can sustain electromechanical waves propagating along flexible plates. We argue that the LEC model can offer a qualitatively new and more realistic description of important properties of active systems with electrical double layers in condensed-matter physics, chemistry, and biology.

`@Article{Alicki2021, author = {Alicki, Robert and Gelbwaser-Klimovsky, David and Jenkins, Alejandro}, journal = {Physical {R}eview {E}}, title = {Leaking elastic capacitor as model for active matter}, year = {2021}, month = may, number = {5}, pages = {052131}, volume = {103}, abstract = {We introduce the ``leaking elastic capacitor'' (LEC) model, a nonconservative dynamical system that combines simple electrical and mechanical degrees of freedom. We show that an LEC connected to an external voltage source can be destabilized (Hopf bifurcation) due to positive feedback between the mechanical separation of the plates and their electrical charging. Numerical simulation finds regimes in which the LEC exhibits a limit cycle (regular self-oscillation) or strange attractors (chaos). The LEC acts as an autonomous engine, cyclically performing work at the expense of the constant voltage source. We show that this mechanical work can be used to pump current, generating an electromotive force without any time-varying magnetic flux and in a thermodynamically irreversible way. We consider how this mechanism can sustain electromechanical waves propagating along flexible plates. We argue that the LEC model can offer a qualitatively new and more realistic description of important properties of active systems with electrical double layers in condensed-matter physics, chemistry, and biology.}, archiveprefix = {arXiv}, doi = {10.1103/PhysRevE.103.052131}, eid = {052131}, eprint = {2010.05534}, keywords = {Physics - Classical Physics, Condensed Matter - Soft Condensed Matter, Physics - Biological Physics, Physics - Chemical Physics}, primaryclass = {physics.class-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021PhRvE.103e2131A}, }`

- Stefano Cusumano and Łukasz Rudnicki. Thermodynamics of Reduced State of the Field.
*Entropy. An International and Interdisciplinary Journal of Entropy and Information Studies*, 23(9):Paper No. 1198, 2021. acknowledgment to ICTQT IRAP project included doi:10.3390/e23091198

[BibTeX] [Download PDF]`@Article{Cusumano2021, author = {Cusumano, Stefano and Rudnicki, Łukasz}, journal = {Entropy. {A}n {I}nternational and {I}nterdisciplinary {J}ournal of {E}ntropy and {I}nformation {S}tudies}, title = {Thermodynamics of {R}educed {S}tate of the {F}ield}, year = {2021}, number = {9}, pages = {Paper No. 1198}, volume = {23}, doi = {10.3390/e23091198}, keywords = {81}, mrnumber = {4320432}, url = {https://www.mdpi.com/1099-4300/23/9/1198/pdf}, note = {acknowledgment to ICTQT IRAP project included} }`

- Marcin Markiewicz and Janusz Przewocki. On construction of finite averaging sets for SL(2,C) via its Cartan decomposition.
*Journal of Physics. A. Mathematical and Theoretical*, 54(23):Paper No. 235302, 20, 2021. doi:10.1088/1751-8121/abfa44

[BibTeX] [Download PDF]`@Article{Markiewicz2021a, author = {Markiewicz, Marcin and Przewocki, Janusz}, journal = {Journal of {P}hysics. {A}. {M}athematical and {T}heoretical}, title = {On construction of finite averaging sets for {SL}(2,{C}) via its {C}artan decomposition}, year = {2021}, issn = {1751-8113}, number = {23}, pages = {Paper No. 235302, 20}, volume = {54}, doi = {10.1088/1751-8121/abfa44}, keywords = {22E30 (05E16 28C10 81P45)}, mrnumber = {4271309}, url = {https://iopscience.iop.org/article/10.1088/1751-8121/abfa44/pdf}, }`

- Łukasz Rudnicki. Quantum speed limit and geometric measure of entanglement.
*Physical Review A*, 104(3):032417, sep 2021. acknowledgment to ICTQT IRAP project included doi:10.1103/PhysRevA.104.032417

[BibTeX] [Abstract] [Download PDF]

Using the approach offered by quantum speed limit, we show that geometric measure of multipartite entanglement for pure states [T.-C. Wei and P. M. Goldbart, Phys. Rev. A 68, 042307 (2003), 10.1103/PhysRevA.68.042307] can be interpreted as the minimal time necessary to unitarily evolve a given quantum state to a separable one.

`@Article{Rudnicki2021, author = {Rudnicki, Łukasz}, journal = {Physical {R}eview {A}}, title = {Quantum speed limit and geometric measure of entanglement}, year = {2021}, month = sep, number = {3}, pages = {032417}, volume = {104}, abstract = {Using the approach offered by quantum speed limit, we show that geometric measure of multipartite entanglement for pure states [T.-C. Wei and P. M. Goldbart, Phys. Rev. A 68, 042307 (2003), 10.1103/PhysRevA.68.042307] can be interpreted as the minimal time necessary to unitarily evolve a given quantum state to a separable one.}, archiveprefix = {arXiv}, doi = {10.1103/PhysRevA.104.032417}, eid = {032417}, eprint = {2107.11877}, groups = {Rudnicki}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021PhRvA.104c2417R}, note = {acknowledgment to ICTQT IRAP project included} }`

- Carlo Maria Scandolo, Roberto Salazar, Jarosław K. Korbicz, and Paweł Horodecki. Universal structure of objective states in all fundamental causal theories.
*Physical Review Research*, 3(3):033148, aug 2021. doi:10.1103/PhysRevResearch.3.033148

[BibTeX] [Abstract] [Download PDF]

A crucial question is how objective and classical behavior arises from a fundamental physical theory. Here we provide a natural definition of a decoherence process valid in all causal theories and show how its behavior can be extremely different from the quantum one. Remarkably, despite this, we prove that the so- called spectrum broadcast structure characterizes all objective states in every fundamental causal theory, exactly as in quantum mechanics. Our results show a stark contrast between the extraordinarily diverse decoherence behavior and the universal features of objectivity.

`@Article{Scandolo2021, author = {Scandolo, Carlo Maria and Salazar, Roberto and Korbicz, Jarosław K. and Horodecki, Paweł}, journal = {Physical {R}eview {R}esearch}, title = {Universal structure of objective states in all fundamental causal theories}, year = {2021}, month = aug, number = {3}, pages = {033148}, volume = {3}, abstract = {A crucial question is how objective and classical behavior arises from a fundamental physical theory. Here we provide a natural definition of a decoherence process valid in all causal theories and show how its behavior can be extremely different from the quantum one. Remarkably, despite this, we prove that the so- called spectrum broadcast structure characterizes all objective states in every fundamental causal theory, exactly as in quantum mechanics. Our results show a stark contrast between the extraordinarily diverse decoherence behavior and the universal features of objectivity.}, doi = {10.1103/PhysRevResearch.3.033148}, eid = {033148}, groups = {Pawel_H}, url = {https://ui.adsabs.harvard.edu/abs/2021PhRvR...3c3148S}, }`

- Markus Grassl. Comment on “An encryption protocol for NEQR images based on one-particle quantum walks on a circle”.
*Quantum Information Processing*, 20(5):183, may 2021. doi:10.1007/s11128-021-03094-0

[BibTeX] [Abstract] [Download PDF]

In [1], the authors propose a protocol to encrypt quantum images. Below we show that the protocol is incorrect.

`@Article{Grassl2021_comment, author = {Grassl, Markus}, journal = {Quantum {I}nformation {P}rocessing}, title = {Comment on "{An} encryption protocol for {NEQR} images based on one-particle quantum walks on a circle"}, year = {2021}, month = may, number = {5}, pages = {183}, volume = {20}, abstract = {In [1], the authors propose a protocol to encrypt quantum images. Below we show that the protocol is incorrect.}, doi = {10.1007/s11128-021-03094-0}, eid = {183}, keywords = {Entanglement, Quantum circuits, Quantum image encryption}, url = {https://ui.adsabs.harvard.edu/abs/2021QuIP...20..183G}, }`

- Klaus Liegener and Łukasz Rudnicki. Algorithmic approach to cosmological coherent state expectation values in loop quantum gravity.
*Classical and Quantum Gravity*, 38(20):Paper No. 205001, 39, 2021. acknowledgment to ICTQT IRAP project included doi:10.1088/1361-6382/ac226f

[BibTeX] [Download PDF]`@Article{Liegener2021, author = {Liegener, Klaus and Rudnicki, Łukasz}, journal = {Classical and {Q}uantum {G}ravity}, title = {Algorithmic approach to cosmological coherent state expectation values in loop quantum gravity}, year = {2021}, issn = {0264-9381}, number = {20}, pages = {Paper No. 205001, 39}, volume = {38}, doi = {10.1088/1361-6382/ac226f}, keywords = {83C45 (83C27)}, mrnumber = {4318548}, url = {https://iopscience.iop.org/article/10.1088/1361-6382/ac226f/pdf}, note = {acknowledgment to ICTQT IRAP project included} }`

- Łukasz Rudnicki and Stephen P. Walborn. Entropic uncertainty relations for mutually unbiased periodic coarse-grained observables resembling their discrete counterparts.
*Physical Review A*, 104(4):Paper No. 042210, 2021. acknowledgment to ICTQT IRAP project included doi:10.1103/physreva.104.042210

[BibTeX] [Download PDF]`@Article{Rudnicki2021a, author = {Rudnicki, Łukasz and Walborn, Stephen P.}, journal = {Physical {R}eview {A}}, title = {Entropic uncertainty relations for mutually unbiased periodic coarse-grained observables resembling their discrete counterparts}, year = {2021}, issn = {2469-9926}, number = {4}, pages = {Paper No. 042210}, volume = {104}, doi = {10.1103/physreva.104.042210}, keywords = {81S07}, mrnumber = {4339485}, url = {https://journals.aps.org/pra/pdf/10.1103/PhysRevA.104.042210}, note = {acknowledgment to ICTQT IRAP project included} }`

- Wooyeong Song, Marcin Wieśniak, Nana Liu, Marcin Pawłowski, Jinhyoung Lee, Jaewan Kim, and Jeongho Bang. Tangible reduction in learning sample complexity with large classical samples and small quantum system.
*Quantum Information Processing*, 20(8):Paper No. 275, 18, 2021. doi:10.1007/s11128-021-03217-7

[BibTeX] [Download PDF]`@Article{Song2021, author = {Song, Wooyeong and Wieśniak, Marcin and Liu, Nana and Pawłowski, Marcin and Lee, Jinhyoung and Kim, Jaewan and Bang, Jeongho}, journal = {Quantum {I}nformation {P}rocessing}, title = {Tangible reduction in learning sample complexity with large classical samples and small quantum system}, year = {2021}, issn = {1570-0755}, number = {8}, pages = {Paper No. 275, 18}, volume = {20}, doi = {10.1007/s11128-021-03217-7}, keywords = {81P68}, mrnumber = {4303621}, url = {https://link.springer.com/content/pdf/10.1007/s11128-021-03217-7.pdf}, }`

- Tamal Guha, Mir Alimuddin, Sumit Rout, Amit Mukherjee, Some Sankar Bhattacharya, and Manik Banik. Quantum Advantage for Shared Randomness Generation.
*Quantum*, 5:569, 2021. acknowledgement for ICTQT IRAP included doi:10.22331/q-2021-10-27-569

[BibTeX] [Download PDF]`@Article{Guha2021, author = {Guha, Tamal and Alimuddin, Mir and Rout, Sumit and Mukherjee, Amit and Bhattacharya, Some Sankar and Banik, Manik}, journal = {Quantum}, title = {Quantum Advantage for Shared Randomness Generation}, note= {acknowledgement for ICTQT IRAP included}, year = {2021}, pages = {569}, volume = {5}, archiveprefix = {arXiv}, doi = {10.22331/q-2021-10-27-569}, eprint = {2001.01889}, primaryclass = {quant-ph}, url = {https://quantum-journal.org/papers/q-2021-10-27-569/pdf/}, doi={10.22331/q-2021-10-27-569}, }`

- Pawel Blasiak, Ewa Borsuk, and Marcin Markiewicz. On safe post-selection for Bell tests with ideal detectors: Causal diagram approach.
*Quantum*, 5:575, 11 2021. doi:10.22331/q-2021-11-11-575

[BibTeX] [Abstract] [Download PDF]

Reasoning about Bell nonlocality from the correlations observed in post-selected data is always a matter of concern. This is because conditioning on the outcomes is a source of non-causal correlations, known as a $\textitselection bias$, rising doubts whether the conclusion concerns the actual causal process or maybe it is just an effect of processing the data. Yet, even in the idealised case without detection inefficiencies, post-selection is an integral part of experimental designs, not least because it is a part of the entanglement generation process itself. In this paper we discuss a broad class of scenarios with post-selection on multiple spatially distributed outcomes. A simple criterion is worked out, called the $\textitall-but-one$ principle, showing when the conclusions about nonlocality from breaking Bell inequalities with post-selected data remain in force. Generality of this result, attained by adopting the high-level diagrammatic tools of causal inference, provides safe grounds for systematic reasoning based on the standard form of multipartite Bell inequalities in a wide array of entanglement generation schemes, without worrying about the dangers of selection bias. In particular, it can be applied to post-selection defined by single-particle events in each detection chanel when the number of particles in the system is conserved.

`@Article{Blasiak2021b, author = {Pawel Blasiak and Ewa Borsuk and Marcin Markiewicz}, journal = {Quantum}, title = {On safe post-selection for {Bell} tests with ideal detectors: {Causal} diagram approach}, year = {2021}, issn = {2521-327X}, month = {11}, pages = {575}, volume = {5}, abstract = {Reasoning about Bell nonlocality from the correlations observed in post-selected data is always a matter of concern. This is because conditioning on the outcomes is a source of non-causal correlations, known as a $\textit{selection bias}$, rising doubts whether the conclusion concerns the actual causal process or maybe it is just an effect of processing the data. Yet, even in the idealised case without detection inefficiencies, post-selection is an integral part of experimental designs, not least because it is a part of the entanglement generation process itself. In this paper we discuss a broad class of scenarios with post-selection on multiple spatially distributed outcomes. A simple criterion is worked out, called the $\textit{all-but-one}$ principle, showing when the conclusions about nonlocality from breaking Bell inequalities with post-selected data remain in force. Generality of this result, attained by adopting the high-level diagrammatic tools of causal inference, provides safe grounds for systematic reasoning based on the standard form of multipartite Bell inequalities in a wide array of entanglement generation schemes, without worrying about the dangers of selection bias. In particular, it can be applied to post-selection defined by single-particle events in each detection chanel when the number of particles in the system is conserved.}, doi = {10.22331/q-2021-11-11-575}, publisher = {Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften}, url = {https://quantum-journal.org/papers/q-2021-11-11-575/pdf/}, }`

- Michał‚ Oszmaniec, Adam Sawicki, and Michał‚ Horodecki. Epsilon-Nets, Unitary Designs and Random Quantum Circuits.
*IEEE Transactions on Information Theory*, PP:1-1, 2021. doi:10.1109/TIT.2021.3128110

[BibTeX] [Abstract] [Download PDF]

Epsilon-nets and approximate unitary t-designs are natural notions that capture properties of unitary operations relevant for numerous applications in quantum information and quantum computing. In this work we study quantitative connections between these two notions. Specifically, we prove that, for d dimensional Hilbert space, unitaries constituting Î´-approximate t-expanders form Ďµ-nets for t â‰� d5/2/Ďµ and Î´ â‰� (Ďµ3/2/d)d2. We also show that for arbitrary t, Ďµ-nets can be used to construct Î´-approximate unitary t-designs for Î´ â‰� Ďµt, where the notion of approximation is based on the diamond norm. Finally, we prove that the degree of an exact unitary t design necessary to obtain an Ďµ-net must grow at least as fast as 1/Ďµ (for fixed dimension) and not slower than d2 (for fixed Ďµ). This shows near optimality of our result connecting t-designs and Ďµ-nets. We apply our findings in the context of quantum computing. First, we show that that approximate t-designs can be generated by shallow random circuits formed from a set of universal two-qudit gates in the parallel and sequential local architectures considered in [1]. Importantly, our gate sets need not to be symmetric (i.e. contains gates together with their inverses) or consist of gates with algebraic entries. Second, we consider compilation of quantum gates and prove a non-constructive Solovay-Kitaev theorem for general universal gate sets. Our main technical contribution is a new construction of efficient polynomial approximations to the Dirac delta in the space of quantum channels, which can be of independent interest.

`@Article{Oszmaniec2021, author = {Michał‚ Oszmaniec and Adam Sawicki and Michał‚ Horodecki}, journal = {IEEE Transactions on Information {T}heory}, title = {Epsilon-{N}ets, {U}nitary {D}esigns and {R}andom {Q}uantum {C}ircuits}, year = {2021}, issn = {1557-9654}, pages = {1--1}, volume = {PP}, abstract = {Epsilon-nets and approximate unitary t-designs are natural notions that capture properties of unitary operations relevant for numerous applications in quantum information and quantum computing. In this work we study quantitative connections between these two notions. Specifically, we prove that, for d dimensional Hilbert space, unitaries constituting Î´-approximate t-expanders form Ďµ-nets for t â‰� d5/2/Ďµ and Î´ â‰� (Ďµ3/2/d)d2. We also show that for arbitrary t, Ďµ-nets can be used to construct Î´-approximate unitary t-designs for Î´ â‰� Ďµt, where the notion of approximation is based on the diamond norm. Finally, we prove that the degree of an exact unitary t design necessary to obtain an Ďµ-net must grow at least as fast as 1/Ďµ (for fixed dimension) and not slower than d2 (for fixed Ďµ). This shows near optimality of our result connecting t-designs and Ďµ-nets. We apply our findings in the context of quantum computing. First, we show that that approximate t-designs can be generated by shallow random circuits formed from a set of universal two-qudit gates in the parallel and sequential local architectures considered in [1]. Importantly, our gate sets need not to be symmetric (i.e. contains gates together with their inverses) or consist of gates with algebraic entries. Second, we consider compilation of quantum gates and prove a non-constructive Solovay-Kitaev theorem for general universal gate sets. Our main technical contribution is a new construction of efficient polynomial approximations to the Dirac delta in the space of quantum channels, which can be of independent interest.}, doi = {10.1109/TIT.2021.3128110}, groups = {Michal_H}, issue = {99}, keywords = {Logic gates, Quantum channels, Quantum computing, Quantum circuit, Layout, Hilbert space, Diamond, unitary designs, epsilon nets, random quantum circuits, compilation of quantum gates, unitary channels}, publisher = {IEEE}, url = {https://arxiv.org/pdf/2007.10885}, }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Żukowski. Can single photon excitation of two spatially separated modes lead to a violation of Bell inequality via weak-field homodyne measurements?.
*New Journal of Physics*, 23(7):073042, jul 2021. doi:10.1088/1367-2630/ac0ffe

[BibTeX] [Abstract] [Download PDF]

We reconsider the all-optical weak homodyne-measurement based experimental schemes aimed at revealing Bell nonclassicality (‘nonlocality’) of a single photon. We focus on the schemes put forward by Tan et al (TWC, 1991) and Hardy (1994). In our previous work we show that the TWC experiment can be described by a local hidden variable model, hence the claimed nonclassicality is apparent. The nonclassicality proof proposed by Hardy remains impeccable. We investigate which feature of the Hardy’s approach is crucial to disclose the nonclassicality. There are consequential differences between TWC and Hardy setups: (i) the initial state of Hardy is a superposition of a single photon excitation with vacuum in one of the input modes of a 50-50 beamsplitter. In the TWC case there is no vacuum component. (ii) In the final measurements of Hardy’s proposal the local settings are specified by the presence or absence of a local oscillator field (on/off). In the TWC case the auxiliary fields are constant, only phases are varied. We show that in Hardy’s setup the violation of local realism occurs due to the varying strength of the local oscillators. Still, one does not need to operate in the fully on/off detection scheme. Thus, the nonclassicality in a Hardy-like setup cannot be attributed to the single-photon state alone. It is a consequence of its interference with the photons from auxiliary local fields. Neither can it be attributed to the joint state of the single photon excitation and the local oscillator modes, as this state is measurement setting dependent. Despite giving spurious violations of local realism, the TWC scheme can serve as an entanglement indicator, for the TWC state. Nevertheless an analogue indicator based on intensity rates rather than just intensities overperforms it.

`@Article{Das2021a, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Żukowski, Marek}, journal = {New Journal of Physics}, title = {Can single photon excitation of two spatially separated modes lead to a violation of {B}ell inequality via weak-field homodyne measurements?}, year = {2021}, month = jul, number = {7}, pages = {073042}, volume = {23}, abstract = {We reconsider the all-optical weak homodyne-measurement based experimental schemes aimed at revealing Bell nonclassicality ('nonlocality') of a single photon. We focus on the schemes put forward by Tan et al (TWC, 1991) and Hardy (1994). In our previous work we show that the TWC experiment can be described by a local hidden variable model, hence the claimed nonclassicality is apparent. The nonclassicality proof proposed by Hardy remains impeccable. We investigate which feature of the Hardy's approach is crucial to disclose the nonclassicality. There are consequential differences between TWC and Hardy setups: (i) the initial state of Hardy is a superposition of a single photon excitation with vacuum in one of the input modes of a 50-50 beamsplitter. In the TWC case there is no vacuum component. (ii) In the final measurements of Hardy's proposal the local settings are specified by the presence or absence of a local oscillator field (on/off). In the TWC case the auxiliary fields are constant, only phases are varied. We show that in Hardy's setup the violation of local realism occurs due to the varying strength of the local oscillators. Still, one does not need to operate in the fully on/off detection scheme. Thus, the nonclassicality in a Hardy-like setup cannot be attributed to the single-photon state alone. It is a consequence of its interference with the photons from auxiliary local fields. Neither can it be attributed to the joint state of the single photon excitation and the local oscillator modes, as this state is measurement setting dependent. Despite giving spurious violations of local realism, the TWC scheme can serve as an entanglement indicator, for the TWC state. Nevertheless an analogue indicator based on intensity rates rather than just intensities overperforms it.}, archiveprefix = {arXiv}, doi = {10.1088/1367-2630/ac0ffe}, eid = {073042}, eprint = {2102.06689}, keywords = {nonclassicality of single photon excitation, Bell inequalities, homodyne measurement, mode entanglement, entanglement witness, operators based on rates, Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021NJPh...23g3042D} }`

- Kamil Korzekwa and Matteo Lostaglio. Quantum Advantage in Simulating Stochastic Processes.
*Physical Review X*, 11(2):021019, 4 2021. doi:10.1103/PhysRevX.11.021019

[BibTeX] [Abstract] [Download PDF]

We investigate the problem of simulating classical stochastic processes through quantum dynamics and present three scenarios where memory or time quantum advantages arise. First, by introducing and analyzing a quantum version of the embeddability problem for stochastic matrices, we show that quantum memoryless dynamics can simulate classical processes that necessarily require memory. Second, by extending the notion of space-time cost of a stochastic process P to the quantum domain, we prove an advantage of the quantum cost of simulating P over the classical cost. Third, we demonstrate that the set of classical states accessible via Markovian master equations with quantum controls is larger than the set of those accessible with classical controls, leading, e.g., to a potential advantage in cooling protocols.

`@Article{Korzekwa2021, author = {Kamil Korzekwa and Matteo Lostaglio}, journal = {Physical Review X}, title = {Quantum Advantage in Simulating Stochastic Processes}, year = {2021}, issn = {2160-3308}, month = {4}, number = {2}, pages = {021019}, volume = {11}, abstract = {We investigate the problem of simulating classical stochastic processes through quantum dynamics and present three scenarios where memory or time quantum advantages arise. First, by introducing and analyzing a quantum version of the embeddability problem for stochastic matrices, we show that quantum memoryless dynamics can simulate classical processes that necessarily require memory. Second, by extending the notion of space-time cost of a stochastic process P to the quantum domain, we prove an advantage of the quantum cost of simulating P over the classical cost. Third, we demonstrate that the set of classical states accessible via Markovian master equations with quantum controls is larger than the set of those accessible with classical controls, leading, e.g., to a potential advantage in cooling protocols.}, doi = {10.1103/PhysRevX.11.021019}, publisher = {American Physical Society}, url = {https://journals.aps.org/prx/pdf/10.1103/PhysRevX.11.021019}, }`

- Karol Horodecki, Michał Studzi’nski, Ryszard P. Kostecki, Omer Sakarya, and Dong Yang. Upper bounds on the leakage of private data and operational approach to markovianity.
*Phys. Rev. A*, 104:052422, 2021. doi:10.1103/PhysRevA.104.052422

[BibTeX] [Download PDF]`@Article{Horodecki2021, author = {Horodecki, Karol and Studzi\'nski, Micha\l{} and Kostecki, Ryszard P. and Sakarya, Omer and Yang, Dong}, journal = {Phys. {R}ev. {A}}, title = {Upper bounds on the leakage of private data and operational approach to markovianity}, year = {2021}, pages = {052422}, volume = {104}, archiveprefix = {arXiv}, doi = {10.1103/PhysRevA.104.052422}, eprint = {2107.10737}, primaryclass = {quant-ph}, url = {https://journals.aps.org/pra/pdf/10.1103/PhysRevA.104.052422}, }`

- Beata Zjawin, Elie Wolfe, and Robert W. Spekkens. Restricted Hidden Cardinality Constraints in Causal Models.
*Electronic Proceedings in Theoretical Computer Science*, (343), dec 2021.

[BibTeX] [Abstract] [Download PDF]

Causal models with unobserved variables impose nontrivial constraints on the distributions over the observed variables. When a common cause of two variables is unobserved, it is impossible to uncover the causal relation between them without making additional assumptions about the model. In this work, we consider causal models with a promise that unobserved variables have known cardinalities. We derive inequality constraints implied by d-separation in such models. Moreover, we explore the possibility of leveraging this result to study causal influence in models that involve quantum systems.

`@article{zjawin2021restricted, author = {Zjawin, Beata and Wolfe, Elie and Spekkens, Robert W}, journal = {Electronic Proceedings in Theoretical Computer Science}, title = {Restricted Hidden Cardinality Constraints in Causal Models}, year = {2021}, month = dec, number = {343}, abstract = {Causal models with unobserved variables impose nontrivial constraints on the distributions over the observed variables. When a common cause of two variables is unobserved, it is impossible to uncover the causal relation between them without making additional assumptions about the model. In this work, we consider causal models with a promise that unobserved variables have known cardinalities. We derive inequality constraints implied by d-separation in such models. Moreover, we explore the possibility of leveraging this result to study causal influence in models that involve quantum systems.}, url = {https://arxiv.org/abs/2109.05656} }`

- Noam Finkelstein, Beata Zjawin, Elie Wolfe, Ilya Shpitser, and Robert W. Spekkens. Entropic Inequality Constraints from e-separation Relations in Directed Acyclic Graphs with Hidden Variables. In
*Uncertainty in Artificial Intelligence*, pages 1045-1055. PMLR,, 2021.

[BibTeX] [Abstract] [Download PDF]

Directed acyclic graphs (DAGs) with hidden vari- ables are often used to characterize causal relations between variables in a system. When some vari- ables are unobserved, DAGs imply a notoriously complicated set of constraints on the distribution of observed variables. In this work, we present en- tropic inequality constraints that are implied by e- separation relations in hidden variable DAGs with discrete observed variables. The constraints can intuitively be understood to follow from the fact that the capacity of variables along a causal path- way to convey information is restricted by their en- tropy; e.g. at the extreme case, a variable with en- tropy 0 can convey no information. We show how these constraints can be used to learn about the true causal model from an observed data distribu- tion. In addition, we propose a measure of causal influence called the minimal mediary entropy, and demonstrate that it can augment traditional mea- sures such as the average causal effect

`@inproceedings{finkelstein2021entropic, title={Entropic Inequality Constraints from e-separation Relations in Directed Acyclic Graphs with Hidden Variables}, author={Finkelstein, Noam and Zjawin, Beata and Wolfe, Elie and Shpitser, Ilya and Spekkens, Robert W}, booktitle={Uncertainty in Artificial Intelligence}, pages={1045--1055}, year={2021}, organization={PMLR}, abstract={Directed acyclic graphs (DAGs) with hidden vari- ables are often used to characterize causal relations between variables in a system. When some vari- ables are unobserved, DAGs imply a notoriously complicated set of constraints on the distribution of observed variables. In this work, we present en- tropic inequality constraints that are implied by e- separation relations in hidden variable DAGs with discrete observed variables. The constraints can intuitively be understood to follow from the fact that the capacity of variables along a causal path- way to convey information is restricted by their en- tropy; e.g. at the extreme case, a variable with en- tropy 0 can convey no information. We show how these constraints can be used to learn about the true causal model from an observed data distribu- tion. In addition, we propose a measure of causal influence called the minimal mediary entropy, and demonstrate that it can augment traditional mea- sures such as the average causal effect}, url={https://arxiv.org/abs/2107.07087} }`

- Gniewomir Sarbicki, Giovanni Scala, and Dariusz Chru’sci’nski. Detection Power of Separability Criteria Based on a Correlation Tensor: A Case Study.
*Open Systems & Information Dynamics*, 28(02), jun 2021. doi:10.1142/S1230161221500104

[BibTeX]`@Article{Sarbicki2021, author = {Gniewomir Sarbicki and Giovanni Scala and Dariusz Chru{\'{s}}ci{\'{n}}ski}, journal = {Open Systems {\&} Information Dynamics}, title = {Detection Power of Separability Criteria Based on a Correlation Tensor: A Case Study}, year = {2021}, month = jun, number = {02}, volume = {28}, doi = {10.1142/S1230161221500104}, publisher = {World Scientific Pub Co Pte Ltd}, }`

- Giovanni Scala, Karolina Słowik, Paolo Facchi, Saverio Pascazio, and Francesco V. Pepe. Beyond the Rabi model: Light interactions with polar atomic systems in a cavity.
*Phys. Rev. A*, 104:013722, Jul 2021. doi:10.1103/PhysRevA.104.013722

[BibTeX] [Download PDF]`@article{PhysRevA.104.013722, title = {Beyond the Rabi model: Light interactions with polar atomic systems in a cavity}, author = {Scala, Giovanni and S\l{}owik, Karolina and Facchi, Paolo and Pascazio, Saverio and Pepe, Francesco V.}, journal = {Phys. Rev. A}, volume = {104}, issue = {1}, pages = {013722}, numpages = {11}, year = {2021}, month = Jul, publisher = {American Physical Society}, doi = {10.1103/PhysRevA.104.013722}, url = {https://link.aps.org/doi/10.1103/PhysRevA.104.013722} }`

- Marcin Markiewicz, Mahasweta Pandit, and Wiesław Laskowski. Simultaneous estimation of multiple phases in generalised Mach–Zehnder interferometer.
*Scientific Reports*, 11(1):15669, Aug 2021. doi:10.1038/s41598-021-95005-7

[BibTeX] [Abstract] [Download PDF]

In this work we investigate the problem of simultaneous estimation of phases using generalised three- and four-mode Mach–Zehnder interferometer. In our setup, we assume that the phases are placed in each of the modes in the interferometer, which introduces correlations between estimators of the phases. These correlations prevent simultaneous estimation of all these phases, however we show that we can still obtain the Heisenberg-like scaling of precision of joint estimation of any subset of \$\$d-1\$\$phases, d being the number of modes, within completely fixed experimental setup, namely with the same initial state and set of measurements. Our estimation scheme can be applied to the task of quantum-enhanced sensing in three-dimensional interferometric configurations.

`@Article{Markiewicz2021SciRep, author={Markiewicz, Marcin and Pandit, Mahasweta and Laskowski, Wies{\l}aw}, title={Simultaneous estimation of multiple phases in generalised {Mach--Zehnder} interferometer}, journal={Scientific Reports}, year={2021}, month=Aug, day={02}, volume={11}, number={1}, pages={15669}, abstract={In this work we investigate the problem of simultaneous estimation of phases using generalised three- and four-mode Mach--Zehnder interferometer. In our setup, we assume that the phases are placed in each of the modes in the interferometer, which introduces correlations between estimators of the phases. These correlations prevent simultaneous estimation of all these phases, however we show that we can still obtain the Heisenberg-like scaling of precision of joint estimation of any subset of {\$}{\$}d-1{\$}{\$}phases, d being the number of modes, within completely fixed experimental setup, namely with the same initial state and set of measurements. Our estimation scheme can be applied to the task of quantum-enhanced sensing in three-dimensional interferometric configurations.}, issn={2045-2322}, doi={10.1038/s41598-021-95005-7}, url={https://doi.org/10.1038/s41598-021-95005-7} }`

- Zbigniew Puchała, Kamil Korzekwa, Roberto Salazar, Paweł Horodecki, and Karol ifmmode dotZelse Żfiyczkowski. Dephasing superchannels.
*Phys. Rev. A*, 104:052611, nov 2021. acknowledgement for ICTQT IRAP included doi:10.1103/PhysRevA.104.052611

[BibTeX] [Download PDF]`@article{puchala_dephasing_2021, author = {Pucha\l{}a, Zbigniew and Korzekwa, Kamil and Salazar, Roberto and Horodecki, Pawe\l{} and \ifmmode \dot{Z}\else \.{Z}\fi{}yczkowski, Karol}, title = {Dephasing superchannels}, note = {acknowledgement for ICTQT IRAP included}, journal = {Phys. Rev. A}, volume = {104}, issue = {5}, pages = {052611}, numpages = {12}, year = {2021}, month = nov, publisher = {American Physical Society}, groups = {Pawel_H}, doi = {10.1103/PhysRevA.104.052611}, url = {https://link.aps.org/doi/10.1103/PhysRevA.104.052611}, }`

- Sumit Rout, Ananda G. Maity, Amit Mukherjee, Saronath Halder, and Manik Banik. Multiparty orthogonal product states with minimal genuine nonlocality.
*Phys. Rev. A*, 104:052433, nov 2021. acknowledgement for ICTQT IRAP included doi:10.1103/PhysRevA.104.052433

[BibTeX] [Abstract] [Download PDF]

Nonlocality without entanglement and its subsequent generalizations offer deep information-theoretic insights and subsequently find several useful applications. The concept of a genuinely nonlocal set of product states emerges as a natural multipartite generalization of this phenomenon. The existence of such sets eventually raises the problem concerning their entanglement-assisted discrimination. Here, we construct examples of genuinely nonlocal product states for an arbitrary number of parties. The strength of genuine nonlocality of these sets can be considered minimal as their perfect discrimination is possible with entangled resources residing in Hilbert spaces having the smallest possible dimensions. Our constructions lead to fully separable measurements that are impossible to implement even if all but one party come together. Furthermore, they also provide the opportunity to compare different multipartite states that otherwise are incomparable under single copy local manipulation.

`@article{Sen_multiparty_2021, title = {Multiparty orthogonal product states with minimal genuine nonlocality}, author = {Rout, Sumit and Maity, Ananda G. and Mukherjee, Amit and Halder, Saronath and Banik, Manik}, journal = {Phys. Rev. A}, note= {acknowledgement for ICTQT IRAP included}, volume = {104}, issue = {5}, pages = {052433}, numpages = {8}, year = {2021}, month = nov, abstract={Nonlocality without entanglement and its subsequent generalizations offer deep information-theoretic insights and subsequently find several useful applications. The concept of a genuinely nonlocal set of product states emerges as a natural multipartite generalization of this phenomenon. The existence of such sets eventually raises the problem concerning their entanglement-assisted discrimination. Here, we construct examples of genuinely nonlocal product states for an arbitrary number of parties. The strength of genuine nonlocality of these sets can be considered minimal as their perfect discrimination is possible with entangled resources residing in Hilbert spaces having the smallest possible dimensions. Our constructions lead to fully separable measurements that are impossible to implement even if all but one party come together. Furthermore, they also provide the opportunity to compare different multipartite states that otherwise are incomparable under single copy local manipulation.}, publisher = {American Physical Society}, groups = {Pawel_H}, doi = {10.1103/PhysRevA.104.052433}, url = {https://link.aps.org/doi/10.1103/PhysRevA.104.052433}, }`

### 2020

- Paweł Mazurek, Máté. Farkas, Andrzej Grudka, Michał Horodecki, and Michał Studziński. Quantum error-correction codes and absolutely maximally entangled states.
*Physical Review A*, 101(4):042305, apr 2020. doi:10.1103/PhysRevA.101.042305

[BibTeX] [Download PDF]`@Article{mazurek_quantum_2020, author = {Mazurek, Paweł and Farkas, Máté and Grudka, Andrzej and Horodecki, Michał and Studziński, Michał}, journal = {Physical {R}eview {A}}, title = {Quantum error-correction codes and absolutely maximally entangled states}, year = {2020}, issn = {2469-9926, 2469-9934}, month = apr, number = {4}, pages = {042305}, volume = {101}, doi = {10.1103/PhysRevA.101.042305}, groups = {Michal_H}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.101.042305}, urldate = {2020-04-22}, }`

- Karol Horodecki and Maciej Stankiewicz. Semi-device-independent quantum money.
*New Journal of Physics*, 22(2):023007, feb 2020. doi:10.1088/1367-2630/ab6872

[BibTeX] [Download PDF]`@Article{horodecki_semi-device-independent_2020, author = {Horodecki, Karol and Stankiewicz, Maciej}, journal = {New {J}ournal of {P}hysics}, title = {Semi-device-independent quantum money}, year = {2020}, issn = {1367-2630}, month = feb, number = {2}, pages = {023007}, volume = {22}, doi = {10.1088/1367-2630/ab6872}, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ab6872}, urldate = {2020-04-22}, }`

- Tomasz Linowski, Grzegorz Rajchel-Mieldzioć, and Karol Życzkowski. Entangling power of multipartite unitary gates.
*Journal of Physics A: Mathematical and Theoretical*, 53(12):125303, mar 2020. doi:10.1088/1751-8121/ab749a

[BibTeX] [Download PDF]`@Article{linowski_entangling_2020, author = {Linowski, Tomasz and Rajchel-Mieldzioć, Grzegorz and Życzkowski, Karol}, journal = {Journal of {P}hysics {A}: {M}athematical and {T}heoretical}, title = {Entangling power of multipartite unitary gates}, year = {2020}, issn = {1751-8113, 1751-8121}, month = mar, number = {12}, pages = {125303}, volume = {53}, doi = {10.1088/1751-8121/ab749a}, url = {https://iopscience.iop.org/article/10.1088/1751-8121/ab749a}, urldate = {2020-04-22}, }`

- Marcin Pawłowski. Entropy in Foundations of Quantum Physics.
*Entropy*, 22(3):371, mar 2020. doi:10.3390/e22030371

[BibTeX] [Abstract] [Download PDF]

Entropy can be used in studies on foundations of quantum physics in many different ways, each of them using different properties of this mathematical object […]

`@article{pawlowski_entropy_2020, title = {Entropy in {Foundations} of {Quantum} {Physics}}, volume = {22}, issn = {1099-4300}, url = {https://www.mdpi.com/1099-4300/22/3/371}, doi = {10.3390/e22030371}, abstract = {Entropy can be used in studies on foundations of quantum physics in many different ways, each of them using different properties of this mathematical object [...]}, language = {en}, number = {3}, urldate = {2020-04-22}, journal = {Entropy}, author = {Pawłowski, Marcin}, month = mar, year = {2020}, pages = {371}, }`

- Massimiliano Smania, Piotr Mironowicz, Mohamed Nawareg, Marcin Pawłowski, Adán Cabello, and Mohamed Bourennane. Experimental certification of an informationally complete quantum measurement in a device-independent protocol.
*Optica*, 7(2):123, feb 2020. doi:10.1364/OPTICA.377959

[BibTeX] [Download PDF]`@article{smania_experimental_2020, title = {Experimental certification of an informationally complete quantum measurement in a device-independent protocol}, volume = {7}, issn = {2334-2536}, url = {https://www.osapublishing.org/abstract.cfm?URI=optica-7-2-123}, doi = {10.1364/OPTICA.377959}, language = {en}, number = {2}, urldate = {2020-04-22}, journal = {Optica}, author = {Smania, Massimiliano and Mironowicz, Piotr and Nawareg, Mohamed and Pawłowski, Marcin and Cabello, Adán and Bourennane, Mohamed}, month = feb, year = {2020}, pages = {123}, }`

- Simon Milz, Fattah Sakuldee, Felix A. Pollock, and Kavan Modi. Kolmogorov extension theorem for (quantum) causal modelling and general probabilistic theories.
*Quantum*, 4:255, apr 2020. doi:10.22331/q-2020-04-20-255

[BibTeX] [Abstract] [Download PDF]

In classical physics, the Kolmogorov extension theorem lays the foundation for the theory of stochastic processes. It has been known for a long time that, in its original form, this theorem does not hold in quantum mechanics. More generally, it does not hold in any theory of stochastic processes — classical, quantum or beyond — that does not just describe passive observations, but allows for active interventions. Such processes form the basis of the study of causal modelling across the sciences, including in the quantum domain. To date, these frameworks have lacked a conceptual underpinning similar to that provided by Kolmogorov’s theorem for classical stochastic processes. We prove a generalized extension theorem that applies to all theories of stochastic processes, putting them on equally firm mathematical ground as their classical counterpart. Additionally, we show that quantum causal modelling and quantum stochastic processes are equivalent. This provides the correct framework for the description of experiments involving continuous control, which play a crucial role in the development of quantum technologies. Furthermore, we show that the original extension theorem follows from the generalized one in the correct limit, and elucidate how a comprehensive understanding of general stochastic processes allows one to unambiguously define the distinction between those that are classical and those that are quantum.

`@Article{milz_kolmogorov_2020, author = {Milz, Simon and Sakuldee, Fattah and Pollock, Felix A. and Modi, Kavan}, journal = {Quantum}, title = {Kolmogorov extension theorem for (quantum) causal modelling and general probabilistic theories}, year = {2020}, issn = {2521-327X}, month = apr, pages = {255}, volume = {4}, abstract = {In classical physics, the Kolmogorov extension theorem lays the foundation for the theory of stochastic processes. It has been known for a long time that, in its original form, this theorem does not hold in quantum mechanics. More generally, it does not hold in any theory of stochastic processes -- classical, quantum or beyond -- that does not just describe passive observations, but allows for active interventions. Such processes form the basis of the study of causal modelling across the sciences, including in the quantum domain. To date, these frameworks have lacked a conceptual underpinning similar to that provided by Kolmogorov’s theorem for classical stochastic processes. We prove a generalized extension theorem that applies to all theories of stochastic processes, putting them on equally firm mathematical ground as their classical counterpart. Additionally, we show that quantum causal modelling and quantum stochastic processes are equivalent. This provides the correct framework for the description of experiments involving continuous control, which play a crucial role in the development of quantum technologies. Furthermore, we show that the original extension theorem follows from the generalized one in the correct limit, and elucidate how a comprehensive understanding of general stochastic processes allows one to unambiguously define the distinction between those that are classical and those that are quantum.}, doi = {10.22331/q-2020-04-20-255}, language = {en}, url = {https://quantum-journal.org/papers/q-2020-04-20-255/}, urldate = {2020-04-22}, }`

- Krzysztof Szczygielski and Robert Alicki. On Howland time-independent formulation of CP-divisible quantum evolutions.
*Reviews in Mathematical Physics*, page 2050021, jan 2020. doi:10.1142/S0129055X2050021X

[BibTeX] [Abstract] [Download PDF]

We extend Howland time-independent formalism to the case of completely positive and trace preserving dynamics of finite-dimensional open quantum systems governed by periodic, time-dependent Lindbladian in Weak Coupling Limit, expanding our result from previous papers. We propose the Bochner space of periodic, square integrable matrix-valued functions, as well as its tensor product representation, as the generalized space of states within the time-independent formalism. We examine some densely defined operators on this space, together with their Fourier-like expansions and address some problems related to their convergence by employing general results on Banach space-valued Fourier series, such as the generalized Carleson–Hunt theorem. We formulate Markovian dynamics in the generalized space of states by constructing appropriate time-independent Lindbladian in standard (Lindblad–Gorini–Kossakowski–Sudarshan) form, as well as one-parameter semigroup of bounded evolution maps. We show their similarity with Markovian generators and dynamical maps defined on matrix space, i.e. the generator still possesses a standard form (extended by closed perturbation) and the resulting semigroup is also completely positive, trace preserving and a contraction.

`@Article{szczygielski_howland_2020, author = {Szczygielski, Krzysztof and Alicki, Robert}, journal = {Reviews in {M}athematical {P}hysics}, title = {On {Howland} time-independent formulation of {CP}-divisible quantum evolutions}, year = {2020}, issn = {0129-055X, 1793-6659}, month = jan, pages = {2050021}, abstract = {We extend Howland time-independent formalism to the case of completely positive and trace preserving dynamics of finite-dimensional open quantum systems governed by periodic, time-dependent Lindbladian in Weak Coupling Limit, expanding our result from previous papers. We propose the Bochner space of periodic, square integrable matrix-valued functions, as well as its tensor product representation, as the generalized space of states within the time-independent formalism. We examine some densely defined operators on this space, together with their Fourier-like expansions and address some problems related to their convergence by employing general results on Banach space-valued Fourier series, such as the generalized Carleson–Hunt theorem. We formulate Markovian dynamics in the generalized space of states by constructing appropriate time-independent Lindbladian in standard (Lindblad–Gorini–Kossakowski–Sudarshan) form, as well as one-parameter semigroup of bounded evolution maps. We show their similarity with Markovian generators and dynamical maps defined on matrix space, i.e. the generator still possesses a standard form (extended by closed perturbation) and the resulting semigroup is also completely positive, trace preserving and a contraction.}, doi = {10.1142/S0129055X2050021X}, language = {en}, url = {https://www.worldscientific.com/doi/abs/10.1142/S0129055X2050021X}, urldate = {2020-05-13}, }`

- Monika Rosicka, Paweł Mazurek, Andrzej Grudka, and Michał Horodecki. Generalized XOR non-locality games with graph description on a square lattice.
*Journal of Physics A: Mathematical and Theoretical*, 53(26):265302, jul 2020. doi:10.1088/1751-8121/ab8f3e

[BibTeX] [Download PDF]`@Article{rosicka_generalized_2020, author = {Rosicka, Monika and Mazurek, Paweł and Grudka, Andrzej and Horodecki, Michał}, journal = {Journal of {P}hysics {A}: {M}athematical and {T}heoretical}, title = {Generalized {XOR} non-locality games with graph description on a square lattice}, year = {2020}, issn = {1751-8113, 1751-8121}, month = jul, number = {26}, pages = {265302}, volume = {53}, doi = {10.1088/1751-8121/ab8f3e}, groups = {Michal_H}, url = {https://iopscience.iop.org/article/10.1088/1751-8121/ab8f3e}, urldate = {2020-06-24}, }`

- Felix Huber and Markus Grassl. Quantum Codes of Maximal Distance and Highly Entangled Subspaces.
*Quantum*, 4:284, jun 2020. doi:10.22331/q-2020-06-18-284

[BibTeX] [Download PDF]`@Article{huber_quantum_2020, author = {Huber, Felix and Grassl, Markus}, journal = {Quantum}, title = {Quantum {Codes} of {Maximal} {Distance} and {Highly} {Entangled} {Subspaces}}, year = {2020}, issn = {2521-327X}, month = jun, pages = {284}, volume = {4}, doi = {10.22331/q-2020-06-18-284}, language = {en}, url = {https://quantum-journal.org/papers/q-2020-06-18-284/}, urldate = {2020-06-24}, }`

- Paul Skrzypczyk, Matty J. Hoban, Ana Belén Sainz, and Noah Linden. Complexity of compatible measurements.
*Physical Review Research*, 2(2):023292, jun 2020. doi:10.1103/PhysRevResearch.2.023292

[BibTeX] [Download PDF]`@Article{skrzypczyk_complexity_2020, author = {Skrzypczyk, Paul and Hoban, Matty J. and Sainz, Ana Belén and Linden, Noah}, journal = {Physical {R}eview {R}esearch}, title = {Complexity of compatible measurements}, year = {2020}, issn = {2643-1564}, month = jun, number = {2}, pages = {023292}, volume = {2}, doi = {10.1103/PhysRevResearch.2.023292}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.023292}, urldate = {2020-06-24}, }`

- Armin Tavakoli, Marek Żukowski, and Časlav Brukner. Does violation of a Bell inequality always imply quantum advantage in a communication complexity problem?.
*Quantum*, 4:316, sep 2020. doi:10.22331/q-2020-09-07-316

[BibTeX] [Abstract] [Download PDF]

Quantum correlations which violate a Bell inequality are presumed to power better-than-classical protocols for solving communication complexity problems (CCPs). How general is this statement? We show that violations of correlation-type Bell inequalities allow advantages in CCPs, when communication protocols are tailored to emulate the Bell no-signaling constraint (by not communicating measurement settings). Abandonment of this restriction on classical models allows us to disprove the main result of, inter alia, \textbackslashcite\BZ02\; we show that quantum correlations obtained from these communication strategies assisted by a small quantum violation of the CGLMP Bell inequalities do not imply advantages in any CCP in the input/output scenario considered in the reference. More generally, we show that there exists quantum correlations, with nontrivial local marginal probabilities, which violate the I 3322 Bell inequality, but do not enable a quantum advantange in any CCP, regardless of the communication strategy employed in the quantum protocol, for a scenario with a fixed number of inputs and outputs

`@Article{tavakoli_does_2020, author = {Tavakoli, Armin and Żukowski, Marek and Brukner, Časlav}, journal = {Quantum}, title = {Does violation of a {Bell} inequality always imply quantum advantage in a communication complexity problem?}, year = {2020}, issn = {2521-327X}, month = sep, pages = {316}, volume = {4}, abstract = {Quantum correlations which violate a Bell inequality are presumed to power better-than-classical protocols for solving communication complexity problems (CCPs). How general is this statement? We show that violations of correlation-type Bell inequalities allow advantages in CCPs, when communication protocols are tailored to emulate the Bell no-signaling constraint (by not communicating measurement settings). Abandonment of this restriction on classical models allows us to disprove the main result of, inter alia, {\textbackslash}cite\{BZ02\}; we show that quantum correlations obtained from these communication strategies assisted by a small quantum violation of the CGLMP Bell inequalities do not imply advantages in any CCP in the input/output scenario considered in the reference. More generally, we show that there exists quantum correlations, with nontrivial local marginal probabilities, which violate the I 3322 Bell inequality, but do not enable a quantum advantange in any CCP, regardless of the communication strategy employed in the quantum protocol, for a scenario with a fixed number of inputs and outputs}, doi = {10.22331/q-2020-09-07-316}, language = {en}, url = {https://quantum-journal.org/papers/q-2020-09-07-316/}, urldate = {2021-05-10}, }`

- Ł. Rudnicki, L. L. Sánchez-Soto, G. Leuchs, and R. W. Boyd. Fundamental quantum limits in ellipsometry.
*Optics Letters*, 45(16):4607, aug 2020. acknowledgment to ICTQT IRAP project included doi:10.1364/OL.392955

[BibTeX] [Download PDF]`@Article{rudnicki_fundamental_2020, author = {Rudnicki, Ł. and Sánchez-Soto, L. L. and Leuchs, G. and Boyd, R. W.}, journal = {Optics {L}etters}, title = {Fundamental quantum limits in ellipsometry}, year = {2020}, issn = {0146-9592, 1539-4794}, month = aug, number = {16}, pages = {4607}, volume = {45}, doi = {10.1364/OL.392955}, language = {en}, url = {https://www.osapublishing.org/abstract.cfm?URI=ol-45-16-4607}, urldate = {2021-05-10}, note = {acknowledgment to ICTQT IRAP project included} }`

- Ana Belén Sainz, Matty J. Hoban, Paul Skrzypczyk, and Leandro Aolita. Bipartite Postquantum Steering in Generalized Scenarios.
*Physical Review Letters*, 125(5):050404, jul 2020. doi:10.1103/PhysRevLett.125.050404

[BibTeX] [Download PDF]`@Article{sainz_bipartite_2020, author = {Sainz, Ana Belén and Hoban, Matty J. and Skrzypczyk, Paul and Aolita, Leandro}, journal = {Physical {R}eview {L}etters}, title = {Bipartite {Postquantum} {Steering} in {Generalized} {Scenarios}}, year = {2020}, issn = {0031-9007, 1079-7114}, month = jul, number = {5}, pages = {050404}, volume = {125}, doi = {10.1103/PhysRevLett.125.050404}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.050404}, urldate = {2021-05-10}, }`

- Sandu Popescu, Ana Belén Sainz, Anthony J. Short, and Andreas Winter. Reference Frames Which Separately Store Noncommuting Conserved Quantities.
*Physical Review Letters*, 125(9):090601, aug 2020. doi:10.1103/PhysRevLett.125.090601

[BibTeX] [Download PDF]`@Article{popescu_reference_2020, author = {Popescu, Sandu and Sainz, Ana Belén and Short, Anthony J. and Winter, Andreas}, journal = {Physical {R}eview {L}etters}, title = {Reference {Frames} {Which} {Separately} {Store} {Noncommuting} {Conserved} {Quantities}}, year = {2020}, issn = {0031-9007, 1079-7114}, month = aug, number = {9}, pages = {090601}, volume = {125}, doi = {10.1103/PhysRevLett.125.090601}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.090601}, urldate = {2021-05-10}, }`

- Debashis Saha, Michał Oszmaniec, Łukasz Czekaj, Michał Horodecki, and Ryszard Horodecki. Operational foundations for complementarity and uncertainty relations.
*Physical Review A*, 101(5):052104, may 2020. doi:10.1103/PhysRevA.101.052104

[BibTeX] [Download PDF]`@Article{saha_operational_2020, author = {Saha, Debashis and Oszmaniec, Michał and Czekaj, Łukasz and Horodecki, Michał and Horodecki, Ryszard}, journal = {Physical {R}eview {A}}, title = {Operational foundations for complementarity and uncertainty relations}, year = {2020}, issn = {2469-9926, 2469-9934}, month = may, number = {5}, pages = {052104}, volume = {101}, doi = {10.1103/PhysRevA.101.052104}, groups = {Michal_H}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.101.052104}, urldate = {2021-05-10}, }`

- Géza Tóth, Tamás Vértesi, Paweł Horodecki, and Ryszard Horodecki. Activating Hidden Metrological Usefulness.
*Physical Review Letters*, 125(2):020402, jul 2020. doi:10.1103/PhysRevLett.125.020402

[BibTeX] [Download PDF]`@Article{toth_activating_2020, author = {Tóth, Géza and Vértesi, Tamás and Horodecki, Paweł and Horodecki, Ryszard}, journal = {Physical {R}eview {L}etters}, title = {Activating {Hidden} {Metrological} {Usefulness}}, year = {2020}, issn = {0031-9007, 1079-7114}, month = jul, number = {2}, pages = {020402}, volume = {125}, doi = {10.1103/PhysRevLett.125.020402}, groups = {Pawel_H}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.125.020402}, urldate = {2021-05-10}, }`

- Karol Horodecki, Ryszard P. Kostecki, Roberto Salazar, and Michał Studziński. Limitations for private randomness repeaters.
*Physical Review A*, 102(1):012615, jul 2020. doi:10.1103/PhysRevA.102.012615

[BibTeX] [Download PDF]`@Article{horodecki_limitations_2020, author = {Horodecki, Karol and Kostecki, Ryszard P. and Salazar, Roberto and Studziński, Michał}, journal = {Physical {R}eview {A}}, title = {Limitations for private randomness repeaters}, year = {2020}, issn = {2469-9926, 2469-9934}, month = jul, number = {1}, pages = {012615}, volume = {102}, doi = {10.1103/PhysRevA.102.012615}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.012615}, urldate = {2021-05-10}, }`

- Anna de Rosier, Jacek Gruca, Fernando Parisio, Tamás Vértesi, and Wiesław Laskowski. Strength and typicality of nonlocality in multisetting and multipartite Bell scenarios.
*Physical Review A*, 101(1):012116, jan 2020. doi:10.1103/PhysRevA.101.012116

[BibTeX] [Download PDF]`@Article{de_rosier_strength_2020, author = {de Rosier, Anna and Gruca, Jacek and Parisio, Fernando and Vértesi, Tamás and Laskowski, Wiesław}, journal = {Physical {R}eview {A}}, title = {Strength and typicality of nonlocality in multisetting and multipartite {Bell} scenarios}, year = {2020}, issn = {2469-9926, 2469-9934}, month = jan, number = {1}, pages = {012116}, volume = {101}, doi = {10.1103/PhysRevA.101.012116}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.101.012116}, urldate = {2021-05-10}, }`

- Lukas Knips, Jan Dziewior, Waldemar Kłobus, Wiesław Laskowski, Tomasz Paterek, Peter J. Shadbolt, Harald Weinfurter, and Jasmin D. A. Meinecke. Multipartite entanglement analysis from random correlations.
*npj Quantum Information*, 6(1):51, dec 2020. doi:10.1038/s41534-020-0281-5

[BibTeX] [Abstract] [Download PDF]

Abstract Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.

`@Article{knips_multipartite_2020, author = {Knips, Lukas and Dziewior, Jan and Kłobus, Waldemar and Laskowski, Wiesław and Paterek, Tomasz and Shadbolt, Peter J. and Weinfurter, Harald and Meinecke, Jasmin D. A.}, journal = {npj {Q}uantum {I}nformation}, title = {Multipartite entanglement analysis from random correlations}, year = {2020}, issn = {2056-6387}, month = dec, number = {1}, pages = {51}, volume = {6}, abstract = {Abstract Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.}, doi = {10.1038/s41534-020-0281-5}, language = {en}, url = {http://www.nature.com/articles/s41534-020-0281-5}, urldate = {2021-05-10}, }`

- Saptarshi Roy, Tamoghna Das, and Aditi Sen(De). Computable genuine multimode entanglement measure: Gaussian versus non-Gaussian.
*Physical Review A*, 102(1):012421, jul 2020. doi:10.1103/PhysRevA.102.012421

[BibTeX] [Download PDF]`@Article{roy_computable_2020, author = {Roy, Saptarshi and Das, Tamoghna and Sen(De), Aditi}, journal = {Physical {R}eview {A}}, title = {Computable genuine multimode entanglement measure: {Gaussian} versus non-{Gaussian}}, year = {2020}, issn = {2469-9926, 2469-9934}, month = jul, number = {1}, pages = {012421}, volume = {102}, doi = {10.1103/PhysRevA.102.012421}, language = {en}, shorttitle = {Computable genuine multimode entanglement measure}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.012421}, urldate = {2021-05-10}, }`

- Elie Wolfe, David Schmid, Ana Belén Sainz, Ravi Kunjwal, and Robert W. Spekkens. Quantifying Bell: the Resource Theory of Nonclassicality of Common-Cause Boxes.
*Quantum*, 4:280, jun 2020. doi:10.22331/q-2020-06-08-280

[BibTeX] [Abstract] [Download PDF]

We take a resource-theoretic approach to the problem of quantifying nonclassicality in Bell scenarios. The resources are conceptualized as probabilistic processes from the setting variables to the outcome variables having a particular causal structure, namely, one wherein the wings are only connected by a common cause. We term them “common-cause boxes”. We define the distinction between classical and nonclassical resources in terms of whether or not a classical causal model can explain the correlations. One can then quantify the relative nonclassicality of resources by considering their interconvertibility relative to the set of operations that can be implemented using a classical common cause (which correspond to local operations and shared randomness). We prove that the set of free operations forms a polytope, which in turn allows us to derive an efficient algorithm for deciding whether one resource can be converted to another. We moreover define two distinct monotones with simple closed-form expressions in the two-party binary-setting binary-outcome scenario, and use these to reveal various properties of the pre-order of resources, including a lower bound on the cardinality of any complete set of monotones. In particular, we show that the information contained in the degrees of violation of facet-defining Bell inequalities is not sufficient for quantifying nonclassicality, even though it is sufficient for witnessing nonclassicality. Finally, we show that the continuous set of convexly extremal quantumly realizable correlations are all at the top of the pre-order of quantumly realizable correlations. In addition to providing new insights on Bell nonclassicality, our work also sets the stage for quantifying nonclassicality in more general causal networks.

`@article{wolfe_quantifying_2020, title = {Quantifying {Bell}: the {Resource} {Theory} of {Nonclassicality} of {Common}-{Cause} {Boxes}}, volume = {4}, issn = {2521-327X}, shorttitle = {Quantifying {Bell}}, url = {https://quantum-journal.org/papers/q-2020-06-08-280/}, doi = {10.22331/q-2020-06-08-280}, abstract = {We take a resource-theoretic approach to the problem of quantifying nonclassicality in Bell scenarios. The resources are conceptualized as probabilistic processes from the setting variables to the outcome variables having a particular causal structure, namely, one wherein the wings are only connected by a common cause. We term them "common-cause boxes". We define the distinction between classical and nonclassical resources in terms of whether or not a classical causal model can explain the correlations. One can then quantify the relative nonclassicality of resources by considering their interconvertibility relative to the set of operations that can be implemented using a classical common cause (which correspond to local operations and shared randomness). We prove that the set of free operations forms a polytope, which in turn allows us to derive an efficient algorithm for deciding whether one resource can be converted to another. We moreover define two distinct monotones with simple closed-form expressions in the two-party binary-setting binary-outcome scenario, and use these to reveal various properties of the pre-order of resources, including a lower bound on the cardinality of any complete set of monotones. In particular, we show that the information contained in the degrees of violation of facet-defining Bell inequalities is not sufficient for quantifying nonclassicality, even though it is sufficient for witnessing nonclassicality. Finally, we show that the continuous set of convexly extremal quantumly realizable correlations are all at the top of the pre-order of quantumly realizable correlations. In addition to providing new insights on Bell nonclassicality, our work also sets the stage for quantifying nonclassicality in more general causal networks.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Wolfe, Elie and Schmid, David and Sainz, Ana Belén and Kunjwal, Ravi and Spekkens, Robert W.}, month = jun, year = {2020}, pages = {280}, }`

- Ravishankar Ramanathan, Monika Rosicka, Karol Horodecki, Stefano Pironio, Michał Horodecki, and Paweł Horodecki. Gadget structures in proofs of the Kochen-Specker theorem.
*Quantum*, 4:308, aug 2020. doi:10.22331/q-2020-08-14-308

[BibTeX] [Abstract] [Download PDF]

The Kochen-Specker theorem is a fundamental result in quantum foundations that has spawned massive interest since its inception. We show that within every Kochen-Specker graph, there exist interesting subgraphs which we term 01 -gadgets, that capture the essential contradiction necessary to prove the Kochen-Specker theorem, i.e,. every Kochen-Specker graph contains a 01 -gadget and from every 01 -gadget one can construct a proof of the Kochen-Specker theorem. Moreover, we show that the 01 -gadgets form a fundamental primitive that can be used to formulate state-independent and state-dependent statistical Kochen-Specker arguments as well as to give simple constructive proofs of an “extended” Kochen-Specker theorem first considered by Pitowsky in \textbackslashcite\Pitowsky\.

`@Article{ramanathan_gadget_2020, author = {Ramanathan, Ravishankar and Rosicka, Monika and Horodecki, Karol and Pironio, Stefano and Horodecki, Michał and Horodecki, Paweł}, journal = {Quantum}, title = {Gadget structures in proofs of the {Kochen}-{Specker} theorem}, year = {2020}, issn = {2521-327X}, month = aug, pages = {308}, volume = {4}, abstract = {The Kochen-Specker theorem is a fundamental result in quantum foundations that has spawned massive interest since its inception. We show that within every Kochen-Specker graph, there exist interesting subgraphs which we term 01 -gadgets, that capture the essential contradiction necessary to prove the Kochen-Specker theorem, i.e,. every Kochen-Specker graph contains a 01 -gadget and from every 01 -gadget one can construct a proof of the Kochen-Specker theorem. Moreover, we show that the 01 -gadgets form a fundamental primitive that can be used to formulate state-independent and state-dependent statistical Kochen-Specker arguments as well as to give simple constructive proofs of an ``extended'' Kochen-Specker theorem first considered by Pitowsky in {\textbackslash}cite\{Pitowsky\}.}, doi = {10.22331/q-2020-08-14-308}, groups = {Pawel_H, Michal_H}, language = {en}, url = {https://quantum-journal.org/papers/q-2020-08-14-308/}, urldate = {2021-05-10}, }`

- Filip B. Maciejewski, Zoltán Zimborás, and Michał Oszmaniec. Mitigation of readout noise in near-term quantum devices by classical post-processing based on detector tomography.
*Quantum*, 4:257, apr 2020. doi:10.22331/q-2020-04-24-257

[BibTeX] [Abstract] [Download PDF]

We propose a simple scheme to reduce readout errors in experiments on quantum systems with finite number of measurement outcomes. Our method relies on performing classical post-processing which is preceded by Quantum Detector Tomography, i.e., the reconstruction of a Positive-Operator Valued Measure (POVM) describing the given quantum measurement device. If the measurement device is affected only by an invertible classical noise, it is possible to correct the outcome statistics of future experiments performed on the same device. To support the practical applicability of this scheme for near-term quantum devices, we characterize measurements implemented in IBM’s and Rigetti’s quantum processors. We find that for these devices, based on superconducting transmon qubits, classical noise is indeed the dominant source of readout errors. Moreover, we analyze the influence of the presence of coherent errors and finite statistics on the performance of our error-mitigation procedure. Applying our scheme on the IBM’s 5-qubit device, we observe a significant improvement of the results of a number of single- and two-qubit tasks including Quantum State Tomography (QST), Quantum Process Tomography (QPT), the implementation of non-projective measurements, and certain quantum algorithms (Grover’s search and the Bernstein-Vazirani algorithm). Finally, we present results showing improvement for the implementation of certain probability distributions in the case of five qubits.

`@article{maciejewski_mitigation_2020, title = {Mitigation of readout noise in near-term quantum devices by classical post-processing based on detector tomography}, volume = {4}, issn = {2521-327X}, url = {https://quantum-journal.org/papers/q-2020-04-24-257/}, doi = {10.22331/q-2020-04-24-257}, abstract = {We propose a simple scheme to reduce readout errors in experiments on quantum systems with finite number of measurement outcomes. Our method relies on performing classical post-processing which is preceded by Quantum Detector Tomography, i.e., the reconstruction of a Positive-Operator Valued Measure (POVM) describing the given quantum measurement device. If the measurement device is affected only by an invertible classical noise, it is possible to correct the outcome statistics of future experiments performed on the same device. To support the practical applicability of this scheme for near-term quantum devices, we characterize measurements implemented in IBM's and Rigetti's quantum processors. We find that for these devices, based on superconducting transmon qubits, classical noise is indeed the dominant source of readout errors. Moreover, we analyze the influence of the presence of coherent errors and finite statistics on the performance of our error-mitigation procedure. Applying our scheme on the IBM's 5-qubit device, we observe a significant improvement of the results of a number of single- and two-qubit tasks including Quantum State Tomography (QST), Quantum Process Tomography (QPT), the implementation of non-projective measurements, and certain quantum algorithms (Grover's search and the Bernstein-Vazirani algorithm). Finally, we present results showing improvement for the implementation of certain probability distributions in the case of five qubits.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Maciejewski, Filip B. and Zimborás, Zoltán and Oszmaniec, Michał}, month = apr, year = {2020}, pages = {257}, }`

- K. Rosołek, M. Wieśniak, and L. Knips. Quadratic Entanglement Criteria for Qutrits.
*Acta Physica Polonica A*, 137(3):374-378, mar 2020. doi:10.12693/APhysPolA.137.374

[BibTeX] [Download PDF]`@Article{rosolek_quadratic_2020, author = {Rosołek, K. and Wieśniak, M. and Knips, L.}, journal = {Acta {P}hysica {P}olonica {A}}, title = {Quadratic {Entanglement} {Criteria} for {Qutrits}}, year = {2020}, issn = {1898-794X, 0587-4246}, month = mar, number = {3}, pages = {374--378}, volume = {137}, doi = {10.12693/APhysPolA.137.374}, url = {http://przyrbwn.icm.edu.pl/APP/PDF/137/app137z3p18.pdf}, urldate = {2021-05-10}, }`

- Marcin Wieśniak, Palash Pandya, Omer Sakarya, and Bianka Woloncewicz. Distance between Bound Entangled States from Unextendible Product Bases and Separable States.
*Quantum Reports*, 2(1):49-56, jan 2020. doi:10.3390/quantum2010004

[BibTeX] [Abstract] [Download PDF]

We discuss the use of the Gilbert algorithm to tailor entanglement witnesses for unextendible product basis bound entangled states (UPB BE states). The method relies on the fact that an optimal entanglement witness is given by a plane perpendicular to a line between the reference state, entanglement of which is to be witnessed, and its closest separable state (CSS). The Gilbert algorithm finds an approximation of CSS. In this article, we investigate if this approximation can be good enough to yield a valid entanglement witness. We compare witnesses found with Gilbert algorithm and those given by Bandyopadhyay–Ghosh–Roychowdhury (BGR) construction. This comparison allows us to learn about the amount of entanglement and we find a relationship between it and a feature of the construction of UPBBE states, namely the size of their central tile. We show that in most studied cases, witnesses found with the Gilbert algorithm in this work are more optimal than ones obtained by Bandyopadhyay, Ghosh, and Roychowdhury. This result implies the increased tolerance to experimental imperfections in a realization of the state.

`@Article{wiesniak_distance_2020, author = {Wieśniak, Marcin and Pandya, Palash and Sakarya, Omer and Woloncewicz, Bianka}, journal = {Quantum {R}eports}, title = {Distance between {Bound} {Entangled} {States} from {Unextendible} {Product} {Bases} and {Separable} {States}}, year = {2020}, issn = {2624-960X}, month = jan, number = {1}, pages = {49--56}, volume = {2}, abstract = {We discuss the use of the Gilbert algorithm to tailor entanglement witnesses for unextendible product basis bound entangled states (UPB BE states). The method relies on the fact that an optimal entanglement witness is given by a plane perpendicular to a line between the reference state, entanglement of which is to be witnessed, and its closest separable state (CSS). The Gilbert algorithm finds an approximation of CSS. In this article, we investigate if this approximation can be good enough to yield a valid entanglement witness. We compare witnesses found with Gilbert algorithm and those given by Bandyopadhyay–Ghosh–Roychowdhury (BGR) construction. This comparison allows us to learn about the amount of entanglement and we find a relationship between it and a feature of the construction of UPBBE states, namely the size of their central tile. We show that in most studied cases, witnesses found with the Gilbert algorithm in this work are more optimal than ones obtained by Bandyopadhyay, Ghosh, and Roychowdhury. This result implies the increased tolerance to experimental imperfections in a realization of the state.}, doi = {10.3390/quantum2010004}, language = {en}, url = {https://www.mdpi.com/2624-960X/2/1/4}, urldate = {2021-05-10}, }`

- Tomasz Linowski, Clemens Gneiting, and Łukasz Rudnicki. Stabilizing entanglement in two-mode Gaussian states.
*Physical Review A*, 102(4):042405, oct 2020. acknowledgment to ICTQT IRAP project included doi:10.1103/PhysRevA.102.042405

[BibTeX] [Download PDF]`@Article{linowski_stabilizing_2020, author = {Linowski, Tomasz and Gneiting, Clemens and Rudnicki, Łukasz}, journal = {Physical {R}eview {A}}, title = {Stabilizing entanglement in two-mode {Gaussian} states}, year = {2020}, issn = {2469-9926, 2469-9934}, month = oct, number = {4}, pages = {042405}, volume = {102}, doi = {10.1103/PhysRevA.102.042405}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.042405}, urldate = {2021-05-10}, note = {acknowledgment to ICTQT IRAP project included} }`

- Michał Eckstein and Paweł Horodecki. The Experiment Paradox in Physics.
*Foundations of Science*, oct 2020. doi:10.1007/s10699-020-09711-y

[BibTeX] [Abstract] [Download PDF]

Abstract Modern physics is founded on two mainstays: mathematical modelling and empirical verification. These two assumptions are prerequisite for the objectivity of scientific discourse. Here we show, however, that they are contradictory, leading to the ‘experiment paradox’. We reveal that any experiment performed on a physical system is—by necessity—invasive and thus establishes inevitable limits to the accuracy of any mathematical model. We track its manifestations in both classical and quantum physics and show how it is overcome ‘in practice’ via the concept of environment. We argue that the unravelled paradox induces a new type of ‘ontic’ underdetermination, which has deep consequences for the methodological foundations of physics.

`@Article{eckstein_experiment_2020, author = {Eckstein, Michał and Horodecki, Paweł}, journal = {Foundations of {S}cience}, title = {The {Experiment} {Paradox} in {Physics}}, year = {2020}, issn = {1233-1821, 1572-8471}, month = oct, abstract = {Abstract Modern physics is founded on two mainstays: mathematical modelling and empirical verification. These two assumptions are prerequisite for the objectivity of scientific discourse. Here we show, however, that they are contradictory, leading to the ‘experiment paradox’. We reveal that any experiment performed on a physical system is—by necessity—invasive and thus establishes inevitable limits to the accuracy of any mathematical model. We track its manifestations in both classical and quantum physics and show how it is overcome ‘in practice’ via the concept of environment. We argue that the unravelled paradox induces a new type of ‘ontic’ underdetermination, which has deep consequences for the methodological foundations of physics.}, doi = {10.1007/s10699-020-09711-y}, groups = {Pawel_H}, language = {en}, url = {http://link.springer.com/10.1007/s10699-020-09711-y}, urldate = {2021-05-10}, }`

- Aaron Z. Goldberg, Andrei B. Klimov, Markus Grassl, Gerd Leuchs, and Luis L. Sánchez-Soto. Extremal quantum states.
*AVS Quantum Science*, 2(4):044701, dec 2020. doi:10.1116/5.0025819

[BibTeX] [Download PDF]`@Article{goldberg_extremal_2020, author = {Goldberg, Aaron Z. and Klimov, Andrei B. and Grassl, Markus and Leuchs, Gerd and Sánchez-Soto, Luis L.}, journal = {AVS {Q}uantum {S}cience}, title = {Extremal quantum states}, year = {2020}, issn = {2639-0213}, month = dec, number = {4}, pages = {044701}, volume = {2}, doi = {10.1116/5.0025819}, language = {en}, url = {http://avs.scitation.org/doi/10.1116/5.0025819}, urldate = {2021-05-10}, }`

- Berry Groisman, Michael Mc Gettrick, Mehdi Mhalla, and Marcin Pawlowski. How Quantum Information Can Improve Social Welfare.
*IEEE Journal on Selected Areas in Information Theory*, 1(2):445-453, aug 2020. doi:10.1109/JSAIT.2020.3012922

[BibTeX] [Download PDF]`@Article{groisman_how_2020, author = {Groisman, Berry and Mc Gettrick, Michael and Mhalla, Mehdi and Pawlowski, Marcin}, journal = {I{EEE} {J}ournal on {S}elected {A}reas in {I}nformation {T}heory}, title = {How {Quantum} {Information} {Can} {Improve} {Social} {Welfare}}, year = {2020}, issn = {2641-8770}, month = aug, number = {2}, pages = {445--453}, volume = {1}, doi = {10.1109/JSAIT.2020.3012922}, url = {https://ieeexplore.ieee.org/document/9173538/}, urldate = {2021-05-10}, }`

- Omer Sakarya, Marek Winczewski, Adam Rutkowski, and Karol Horodecki. Hybrid quantum network design against unauthorized secret-key generation, and its memory cost.
*Physical Review Research*, 2(4):043022, oct 2020. doi:10.1103/PhysRevResearch.2.043022

[BibTeX] [Download PDF]`@Article{sakarya_hybrid_2020, author = {Sakarya, Omer and Winczewski, Marek and Rutkowski, Adam and Horodecki, Karol}, journal = {Physical {R}eview {R}esearch}, title = {Hybrid quantum network design against unauthorized secret-key generation, and its memory cost}, year = {2020}, issn = {2643-1564}, month = oct, number = {4}, pages = {043022}, volume = {2}, doi = {10.1103/PhysRevResearch.2.043022}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.043022}, urldate = {2021-05-10}, }`

- John H. Selby and Ciarán M. Lee. Compositional resource theories of coherence.
*Quantum*, 4:319, sep 2020. doi:10.22331/q-2020-09-11-319

[BibTeX] [Abstract] [Download PDF]

Quantum coherence is one of the most important resources in quantum information theory. Indeed, preventing the loss of coherence is one of the most important technical challenges obstructing the development of large-scale quantum computers. Recently, there has been substantial progress in developing mathematical resource theories of coherence, paving the way towards its quantification and control. To date however, these resource theories have only been mathematically formalised within the realms of convex-geometry, information theory, and linear algebra. This approach is limited in scope, and makes it difficult to generalise beyond resource theories of coherence for single system quantum states. In this paper we take a complementary perspective, showing that resource theories of coherence can instead be defined purely compositionally, that is, working with the mathematics of process theories, string diagrams and category theory. This new perspective offers several advantages: i) it unifies various existing approaches to the study of coherence, for example, subsuming both speakable and unspeakable coherence; ii) it provides a general treatment of the compositional multi-system setting; iii) it generalises immediately to the case of quantum channels, measurements, instruments, and beyond rather than just states; iv) it can easily be generalised to the setting where there are multiple distinct sources of decoherence; and, iv) it directly extends to arbitrary process theories, for example, generalised probabilistic theories and Spekkens toy model—providing the ability to operationally characterise coherence rather than relying on specific mathematical features of quantum theory for its description. More importantly, by providing a new, complementary, perspective on the resource of coherence, this work opens the door to the development of novel tools which would not be accessible from the linear algebraic mind set.

`@article{selby_compositional_2020, title = {Compositional resource theories of coherence}, volume = {4}, issn = {2521-327X}, url = {https://quantum-journal.org/papers/q-2020-09-11-319/}, doi = {10.22331/q-2020-09-11-319}, abstract = {Quantum coherence is one of the most important resources in quantum information theory. Indeed, preventing the loss of coherence is one of the most important technical challenges obstructing the development of large-scale quantum computers. Recently, there has been substantial progress in developing mathematical resource theories of coherence, paving the way towards its quantification and control. To date however, these resource theories have only been mathematically formalised within the realms of convex-geometry, information theory, and linear algebra. This approach is limited in scope, and makes it difficult to generalise beyond resource theories of coherence for single system quantum states. In this paper we take a complementary perspective, showing that resource theories of coherence can instead be defined purely compositionally, that is, working with the mathematics of process theories, string diagrams and category theory. This new perspective offers several advantages: i) it unifies various existing approaches to the study of coherence, for example, subsuming both speakable and unspeakable coherence; ii) it provides a general treatment of the compositional multi-system setting; iii) it generalises immediately to the case of quantum channels, measurements, instruments, and beyond rather than just states; iv) it can easily be generalised to the setting where there are multiple distinct sources of decoherence; and, iv) it directly extends to arbitrary process theories, for example, generalised probabilistic theories and Spekkens toy model---providing the ability to operationally characterise coherence rather than relying on specific mathematical features of quantum theory for its description. More importantly, by providing a new, complementary, perspective on the resource of coherence, this work opens the door to the development of novel tools which would not be accessible from the linear algebraic mind set.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Selby, John H. and Lee, Ciarán M.}, month = sep, year = {2020}, pages = {319}, }`

- Palash Pandya, Omer Sakarya, and Marcin Wieśniak. Hilbert-Schmidt distance and entanglement witnessing.
*Physical Review A*, 102(1):012409, jul 2020. doi:10.1103/PhysRevA.102.012409

[BibTeX] [Download PDF]`@Article{pandya_hilbert-schmidt_2020, author = {Pandya, Palash and Sakarya, Omer and Wieśniak, Marcin}, journal = {Physical {R}eview {A}}, title = {Hilbert-{Schmidt} distance and entanglement witnessing}, year = {2020}, issn = {2469-9926, 2469-9934}, month = jul, number = {1}, pages = {012409}, volume = {102}, doi = {10.1103/PhysRevA.102.012409}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.012409}, urldate = {2021-05-10}, }`

- Jamie Sikora and John H. Selby. Impossibility of coin flipping in generalized probabilistic theories via discretizations of semi-infinite programs.
*Physical Review Research*, 2(4):043128, oct 2020. doi:10.1103/PhysRevResearch.2.043128

[BibTeX] [Download PDF]`@Article{sikora_impossibility_2020, author = {Sikora, Jamie and Selby, John H.}, journal = {Physical {R}eview {R}esearch}, title = {Impossibility of coin flipping in generalized probabilistic theories via discretizations of semi-infinite programs}, year = {2020}, issn = {2643-1564}, month = oct, number = {4}, pages = {043128}, volume = {2}, doi = {10.1103/PhysRevResearch.2.043128}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.043128}, urldate = {2021-05-10}, }`

- Alley Hameedi, Breno Marques, Piotr Mironowicz, Debashis Saha, Marcin Pawłowski, and Mohamed Bourennane. Experimental test of nonclassicality with arbitrarily low detection efficiency.
*Physical Review A*, 102(3):032621, sep 2020. doi:10.1103/PhysRevA.102.032621

[BibTeX] [Download PDF]`@Article{hameedi_experimental_2020, author = {Hameedi, Alley and Marques, Breno and Mironowicz, Piotr and Saha, Debashis and Pawłowski, Marcin and Bourennane, Mohamed}, journal = {Physical {R}eview {A}}, title = {Experimental test of nonclassicality with arbitrarily low detection efficiency}, year = {2020}, issn = {2469-9926, 2469-9934}, month = sep, number = {3}, pages = {032621}, volume = {102}, doi = {10.1103/PhysRevA.102.032621}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.032621}, urldate = {2021-05-10}, }`

- Thao P. Le, Piotr Mironowicz, and Paweł Horodecki. Blurred quantum Darwinism across quantum reference frames.
*Physical Review A*, 102(6):062420, dec 2020. doi:10.1103/PhysRevA.102.062420

[BibTeX] [Download PDF]`@Article{le_blurred_2020, author = {Le, Thao P. and Mironowicz, Piotr and Horodecki, Paweł}, journal = {Physical {R}eview {A}}, title = {Blurred quantum {Darwinism} across quantum reference frames}, year = {2020}, issn = {2469-9926, 2469-9934}, month = dec, number = {6}, pages = {062420}, volume = {102}, doi = {10.1103/PhysRevA.102.062420}, groups = {Pawel_H}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.062420}, urldate = {2021-05-10}, }`

- Sudha, H. S. Karthik, Rajarshi Pal, K. S. Akhilesh, Sibasish Ghosh, K. S. Mallesh, and A. R. Usha Devi. Canonical forms of two-qubit states under local operations.
*Physical Review A*, 102(5):052419, nov 2020. doi:10.1103/PhysRevA.102.052419

[BibTeX] [Download PDF]`@Article{sudha_canonical_2020, author = {{Sudha} and Karthik, H. S. and Pal, Rajarshi and Akhilesh, K. S. and Ghosh, Sibasish and Mallesh, K. S. and Usha Devi, A. R.}, journal = {Physical {R}eview {A}}, title = {Canonical forms of two-qubit states under local operations}, year = {2020}, issn = {2469-9926, 2469-9934}, month = nov, number = {5}, pages = {052419}, volume = {102}, doi = {10.1103/PhysRevA.102.052419}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.102.052419}, urldate = {2021-05-10}, }`

- Anubhav Chaturvedi and Debashis Saha. Quantum prescriptions are more ontologically distinct than they are operationally distinguishable.
*Quantum*, 4:345, oct 2020. doi:10.22331/q-2020-10-21-345

[BibTeX] [Abstract] [Download PDF]

Based on an intuitive generalization of the Leibniz principle of `the identity of indiscernibles’, we introduce a novel ontological notion of classicality, called bounded ontological distinctness. Formulated as a principle, bounded ontological distinctness equates the distinguishability of a set of operational physical entities to the distinctness of their ontological counterparts. Employing three instances of two-dimensional quantum preparations, we demonstrate the violation of bounded ontological distinctness or excess ontological distinctness of quantum preparations, without invoking any additional assumptions. Moreover, our methodology enables the inference of tight lower bounds on the extent of excess ontological distinctness of quantum preparations. Similarly, we demonstrate excess ontological distinctness of quantum transformations, using three two-dimensional unitary transformations. However, to demonstrate excess ontological distinctness of quantum measurements, an additional assumption such as outcome determinism or bounded ontological distinctness of preparations is required. Moreover, we show that quantum violations of other well-known ontological principles implicate quantum excess ontological distinctness. Finally, to showcase the operational vitality of excess ontological distinctness, we introduce two distinct classes of communication tasks powered by excess ontological distinctness.

`@article{chaturvedi_quantum_2020, title = {Quantum prescriptions are more ontologically distinct than they are operationally distinguishable}, volume = {4}, issn = {2521-327X}, url = {https://quantum-journal.org/papers/q-2020-10-21-345/}, doi = {10.22331/q-2020-10-21-345}, abstract = {Based on an intuitive generalization of the Leibniz principle of `the identity of indiscernibles', we introduce a novel ontological notion of classicality, called bounded ontological distinctness. Formulated as a principle, bounded ontological distinctness equates the distinguishability of a set of operational physical entities to the distinctness of their ontological counterparts. Employing three instances of two-dimensional quantum preparations, we demonstrate the violation of bounded ontological distinctness or excess ontological distinctness of quantum preparations, without invoking any additional assumptions. Moreover, our methodology enables the inference of tight lower bounds on the extent of excess ontological distinctness of quantum preparations. Similarly, we demonstrate excess ontological distinctness of quantum transformations, using three two-dimensional unitary transformations. However, to demonstrate excess ontological distinctness of quantum measurements, an additional assumption such as outcome determinism or bounded ontological distinctness of preparations is required. Moreover, we show that quantum violations of other well-known ontological principles implicate quantum excess ontological distinctness. Finally, to showcase the operational vitality of excess ontological distinctness, we introduce two distinct classes of communication tasks powered by excess ontological distinctness.}, language = {en}, urldate = {2021-05-10}, journal = {Quantum}, author = {Chaturvedi, Anubhav and Saha, Debashis}, month = oct, year = {2020}, pages = {345}, }`

- Michał Eckstein, Paweł Horodecki, Ryszard Horodecki, and Tomasz Miller. Operational causality in spacetime.
*Physical Review A*, 101(4):042128, apr 2020. arXiv: 1902.05002 doi:10.1103/PhysRevA.101.042128

[BibTeX] [Abstract] [Download PDF]

The no-signalling principle preventing superluminal communication is a limiting paradigm for physical theories. Within the information-theoretic framework it is commonly understood in terms of admissible correlations in composite systems. Here we unveil its complementary incarnation — the ‘dynamical no-signalling principle’ —, which forbids superluminal signalling via measurements on simple physical objects (e.g. particles) evolving in time. We show that it imposes strong constraints on admissible models of dynamics. The posited principle is universal — it can be applied to any theory (classical, quantum or post-quantum) with well-defined rules of calculating detection statistics in spacetime. As an immediate application we show how one could exploit the Schr\textbackslash”odinger equation to establish a fully operational superluminal protocol in the Minkowski spacetime. This example illustrates how the principle can be used to identify the limits of applicability of a given model of quantum or post-quantum dynamics.

`@Article{eckstein_operational_2020, author = {Eckstein, Michał and Horodecki, Paweł and Horodecki, Ryszard and Miller, Tomasz}, journal = {Physical {R}eview {A}}, title = {Operational causality in spacetime}, year = {2020}, issn = {2469-9926, 2469-9934}, month = apr, note = {arXiv: 1902.05002}, number = {4}, pages = {042128}, volume = {101}, abstract = {The no-signalling principle preventing superluminal communication is a limiting paradigm for physical theories. Within the information-theoretic framework it is commonly understood in terms of admissible correlations in composite systems. Here we unveil its complementary incarnation --- the 'dynamical no-signalling principle' ---, which forbids superluminal signalling via measurements on simple physical objects (e.g. particles) evolving in time. We show that it imposes strong constraints on admissible models of dynamics. The posited principle is universal --- it can be applied to any theory (classical, quantum or post-quantum) with well-defined rules of calculating detection statistics in spacetime. As an immediate application we show how one could exploit the Schr{\textbackslash}"odinger equation to establish a fully operational superluminal protocol in the Minkowski spacetime. This example illustrates how the principle can be used to identify the limits of applicability of a given model of quantum or post-quantum dynamics.}, doi = {10.1103/PhysRevA.101.042128}, groups = {Pawel_H}, keywords = {Quantum Physics, General Relativity and Quantum Cosmology, Mathematical Physics, 81P16 (Primary), 81P15, 28E99, 60B05 (Secondary)}, url = {http://arxiv.org/abs/1902.05002}, urldate = {2021-05-11}, }`

- Marcin Łobejko, Paweł Mazurek, and Michał Horodecki. Thermodynamics of Minimal Coupling Quantum Heat Engines.
*Quantum*, 4:375, dec 2020. arXiv: 2003.05788 doi:10.22331/q-2020-12-23-375

[BibTeX] [Abstract] [Download PDF]

The minimal-coupling quantum heat engine is a thermal machine consisting of an explicit energy storage system, heat baths, and a working body, which alternatively couples to subsystems through discrete strokes — energy-conserving two-body quantum operations. Within this paradigm, we present a general framework of quantum thermodynamics, where a work extraction process is fundamentally limited by a flow of non-passive energy (ergotropy), while energy dissipation is expressed through a flow of passive energy. It turns out that small dimensionality of the working body and a restriction only to two-body operations make the engine fundamentally irreversible. Our main result is finding the optimal efficiency and work production per cycle within the whole class of irreversible minimal-coupling engines composed of three strokes and with the two-level working body, where we take into account all possible quantum correlations between the working body and the battery. One of the key new tools is the introduced “control-marginal state” — one which acts only on a working body Hilbert space, but encapsulates all features regarding work extraction of the total working body-battery system. In addition, we propose a generalization of the many-stroke engine, and we analyze efficiency vs extracted work trade-offs, as well as work fluctuations after many cycles of the running of the engine.

`@Article{lobejko_thermodynamics_2020, author = {Łobejko, Marcin and Mazurek, Paweł and Horodecki, Michał}, journal = {Quantum}, title = {Thermodynamics of {Minimal} {Coupling} {Quantum} {Heat} {Engines}}, year = {2020}, issn = {2521-327X}, month = dec, note = {arXiv: 2003.05788}, pages = {375}, volume = {4}, abstract = {The minimal-coupling quantum heat engine is a thermal machine consisting of an explicit energy storage system, heat baths, and a working body, which alternatively couples to subsystems through discrete strokes -- energy-conserving two-body quantum operations. Within this paradigm, we present a general framework of quantum thermodynamics, where a work extraction process is fundamentally limited by a flow of non-passive energy (ergotropy), while energy dissipation is expressed through a flow of passive energy. It turns out that small dimensionality of the working body and a restriction only to two-body operations make the engine fundamentally irreversible. Our main result is finding the optimal efficiency and work production per cycle within the whole class of irreversible minimal-coupling engines composed of three strokes and with the two-level working body, where we take into account all possible quantum correlations between the working body and the battery. One of the key new tools is the introduced "control-marginal state" -- one which acts only on a working body Hilbert space, but encapsulates all features regarding work extraction of the total working body-battery system. In addition, we propose a generalization of the many-stroke engine, and we analyze efficiency vs extracted work trade-offs, as well as work fluctuations after many cycles of the running of the engine.}, doi = {10.22331/q-2020-12-23-375}, groups = {Michal_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2003.05788}, urldate = {2021-07-28}, }`

- Cristina Cirstoiu, Kamil Korzekwa, and David Jennings. Robustness of Noether’s principle: Maximal disconnects between conservation laws and symmetries in quantum theory.
*Physical Review X*, 10(4):041035, nov 2020. arXiv: 1908.04254 doi:10.1103/PhysRevX.10.041035

[BibTeX] [Abstract] [Download PDF]

To what extent does Noether’s principle apply to quantum channels? Here, we quantify the degree to which imposing a symmetry constraint on quantum channels implies a conservation law, and show that this relates to physically impossible transformations in quantum theory, such as time-reversal and spin-inversion. In this analysis, the convex structure and extremal points of the set of quantum channels symmetric under the action of a Lie group \$G\$ becomes essential. It allows us to derive bounds on the deviation from conservation laws under any symmetric quantum channel in terms of the deviation from closed dynamics as measured by the unitarity of the channel. In particular, we investigate in detail the \$U(1)\$ and \$SU(2)\$ symmetries related to energy and angular momentum conservation laws. In the latter case, we provide fundamental limits on how much a spin-\$j\_A\$ system can be used to polarise a larger spin-\$j\_B\$ system, and on how much one can invert spin polarisation using a rotationally-symmetric operation. Finally, we also establish novel links between unitarity, complementary channels and purity that are of independent interest.

`@Article{cirstoiu_robustness_2020, author = {Cirstoiu, Cristina and Korzekwa, Kamil and Jennings, David}, journal = {Physical {R}eview {X}}, title = {Robustness of {Noether}'s principle: {Maximal} disconnects between conservation laws and symmetries in quantum theory}, year = {2020}, issn = {2160-3308}, month = nov, note = {arXiv: 1908.04254}, number = {4}, pages = {041035}, volume = {10}, abstract = {To what extent does Noether's principle apply to quantum channels? Here, we quantify the degree to which imposing a symmetry constraint on quantum channels implies a conservation law, and show that this relates to physically impossible transformations in quantum theory, such as time-reversal and spin-inversion. In this analysis, the convex structure and extremal points of the set of quantum channels symmetric under the action of a Lie group \$G\$ becomes essential. It allows us to derive bounds on the deviation from conservation laws under any symmetric quantum channel in terms of the deviation from closed dynamics as measured by the unitarity of the channel. In particular, we investigate in detail the \$U(1)\$ and \$SU(2)\$ symmetries related to energy and angular momentum conservation laws. In the latter case, we provide fundamental limits on how much a spin-\$j\_A\$ system can be used to polarise a larger spin-\$j\_B\$ system, and on how much one can invert spin polarisation using a rotationally-symmetric operation. Finally, we also establish novel links between unitarity, complementary channels and purity that are of independent interest.}, doi = {10.1103/PhysRevX.10.041035}, keywords = {Quantum Physics}, shorttitle = {Robustness of {Noether}'s principle}, url = {http://arxiv.org/abs/1908.04254}, urldate = {2021-07-28}, }`

- Daniel Jost Brod and Michał Oszmaniec. Classical simulation of linear optics subject to nonuniform losses.
*Quantum*, 4:267, may 2020. arXiv: 1906.06696 doi:10.22331/q-2020-05-14-267

[BibTeX] [Abstract] [Download PDF]

We present a comprehensive study of the impact of non-uniform, i.e.\textbackslash path-dependent, photonic losses on the computational complexity of linear-optical processes. Our main result states that, if each beam splitter in a network induces some loss probability, non-uniform network designs cannot circumvent the efficient classical simulations based on losses. To achieve our result we obtain new intermediate results that can be of independent interest. First, we show that, for any network of lossy beam-splitters, it is possible to extract a layer of non-uniform losses that depends on the network geometry. We prove that, for every input mode of the network it is possible to commute \$s\_i\$ layers of losses to the input, where \$s\_i\$ is the length of the shortest path connecting the \$i\$th input to any output. We then extend a recent classical simulation algorithm due to P. Clifford and R. Clifford to allow for arbitrary \$n\$-photon input Fock states (i.e. to include collision states). Consequently, we identify two types of input states where boson sampling becomes classically simulable: (A) when \$n\$ input photons occupy a constant number of input modes; (B) when all but \$O(\textbackslashlog n)\$ photons are concentrated on a single input mode, while an additional \$O(\textbackslashlog n)\$ modes contain one photon each.

`@Article{brod_classical_2020, author = {Brod, Daniel Jost and Oszmaniec, Michał}, journal = {Quantum}, title = {Classical simulation of linear optics subject to nonuniform losses}, year = {2020}, issn = {2521-327X}, month = may, note = {arXiv: 1906.06696}, pages = {267}, volume = {4}, abstract = {We present a comprehensive study of the impact of non-uniform, i.e.{\textbackslash} path-dependent, photonic losses on the computational complexity of linear-optical processes. Our main result states that, if each beam splitter in a network induces some loss probability, non-uniform network designs cannot circumvent the efficient classical simulations based on losses. To achieve our result we obtain new intermediate results that can be of independent interest. First, we show that, for any network of lossy beam-splitters, it is possible to extract a layer of non-uniform losses that depends on the network geometry. We prove that, for every input mode of the network it is possible to commute \$s\_i\$ layers of losses to the input, where \$s\_i\$ is the length of the shortest path connecting the \$i\$th input to any output. We then extend a recent classical simulation algorithm due to P. Clifford and R. Clifford to allow for arbitrary \$n\$-photon input Fock states (i.e. to include collision states). Consequently, we identify two types of input states where boson sampling becomes classically simulable: (A) when \$n\$ input photons occupy a constant number of input modes; (B) when all but \$O({\textbackslash}log n)\$ photons are concentrated on a single input mode, while an additional \$O({\textbackslash}log n)\$ modes contain one photon each.}, doi = {10.22331/q-2020-05-14-267}, keywords = {Quantum Physics, Mathematical Physics}, url = {http://arxiv.org/abs/1906.06696}, urldate = {2021-07-28}, }`

- Michał Eckstein, Paweł Horodecki, Ryszard Horodecki, and Tomasz Miller. Operational causality in spacetime.
*Physical Review A*, 101(4):042128, apr 2020. arXiv: 1902.05002 doi:10.1103/PhysRevA.101.042128

[BibTeX] [Abstract] [Download PDF]

The no-signalling principle preventing superluminal communication is a limiting paradigm for physical theories. Within the information-theoretic framework it is commonly understood in terms of admissible correlations in composite systems. Here we unveil its complementary incarnation — the ‘dynamical no-signalling principle’ —, which forbids superluminal signalling via measurements on simple physical objects (e.g. particles) evolving in time. We show that it imposes strong constraints on admissible models of dynamics. The posited principle is universal — it can be applied to any theory (classical, quantum or post-quantum) with well-defined rules of calculating detection statistics in spacetime. As an immediate application we show how one could exploit the Schr\textbackslash”odinger equation to establish a fully operational superluminal protocol in the Minkowski spacetime. This example illustrates how the principle can be used to identify the limits of applicability of a given model of quantum or post-quantum dynamics.

`@Article{eckstein_operational_2020-1, author = {Eckstein, Michał and Horodecki, Paweł and Horodecki, Ryszard and Miller, Tomasz}, journal = {Physical {R}eview {A}}, title = {Operational causality in spacetime}, year = {2020}, issn = {2469-9926, 2469-9934}, month = apr, note = {arXiv: 1902.05002}, number = {4}, pages = {042128}, volume = {101}, abstract = {The no-signalling principle preventing superluminal communication is a limiting paradigm for physical theories. Within the information-theoretic framework it is commonly understood in terms of admissible correlations in composite systems. Here we unveil its complementary incarnation --- the 'dynamical no-signalling principle' ---, which forbids superluminal signalling via measurements on simple physical objects (e.g. particles) evolving in time. We show that it imposes strong constraints on admissible models of dynamics. The posited principle is universal --- it can be applied to any theory (classical, quantum or post-quantum) with well-defined rules of calculating detection statistics in spacetime. As an immediate application we show how one could exploit the Schr{\textbackslash}"odinger equation to establish a fully operational superluminal protocol in the Minkowski spacetime. This example illustrates how the principle can be used to identify the limits of applicability of a given model of quantum or post-quantum dynamics.}, doi = {10.1103/PhysRevA.101.042128}, groups = {Pawel_H}, keywords = {Quantum Physics, General Relativity and Quantum Cosmology, Mathematical Physics, 81P16 (Primary), 81P15, 28E99, 60B05 (Secondary)}, url = {http://arxiv.org/abs/1902.05002}, urldate = {2021-07-28}, }`

- Jakub Czartowski, Dardo Goyeneche, Markus Grassl, and Karol Życzkowski. Isoentangled Mutually Unbiased Bases, Symmetric Quantum Measurements, and Mixed-State Designs.
*Physical Review Letters*, 124(9):090503, mar 2020. doi:10.1103/PhysRevLett.124.090503

[BibTeX] [Download PDF]`@Article{czartowski_isoentangled_2020, author = {Czartowski, Jakub and Goyeneche, Dardo and Grassl, Markus and Życzkowski, Karol}, journal = {Physical {R}eview {L}etters}, title = {Isoentangled {Mutually} {Unbiased} {Bases}, {Symmetric} {Quantum} {Measurements}, and {Mixed}-{State} {Designs}}, year = {2020}, issn = {0031-9007, 1079-7114}, month = mar, number = {9}, pages = {090503}, volume = {124}, doi = {10.1103/PhysRevLett.124.090503}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.124.090503}, urldate = {2020-04-22}, }`

- Robert Alicki and Alejandro Jenkins. Quantum Theory of Triboelectricity.
*Physical Review Letters*, 125(18):186101, oct 2020. doi:10.1103/PhysRevLett.125.186101

[BibTeX] [Abstract] [Download PDF]

We propose a microphysical theory of the triboelectric effect by which mechanical rubbing separates charges across the interface between two materials. Surface electrons are treated as an open system coupled to two baths, corresponding to the bulks. Extending Zel’dovich’s theory of bosonic superradiance, we show that motion-induced population inversion can generate an electromotive force. We argue that this is consistent with the basic phenomenology of triboelectrification and triboluminescence as irreversible processes, and we suggest how to carry out more precise experimental tests.

`@Article{Alicki2020, author = {Alicki, Robert and Jenkins, Alejandro}, journal = {Physical {R}eview {L}etters}, title = {Quantum Theory of Triboelectricity}, year = {2020}, month = oct, number = {18}, pages = {186101}, volume = {125}, abstract = {We propose a microphysical theory of the triboelectric effect by which mechanical rubbing separates charges across the interface between two materials. Surface electrons are treated as an open system coupled to two baths, corresponding to the bulks. Extending Zel'dovich's theory of bosonic superradiance, we show that motion-induced population inversion can generate an electromotive force. We argue that this is consistent with the basic phenomenology of triboelectrification and triboluminescence as irreversible processes, and we suggest how to carry out more precise experimental tests.}, archiveprefix = {arXiv}, doi = {10.1103/PhysRevLett.125.186101}, eid = {186101}, eprint = {1904.11997}, keywords = {Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Statistical Mechanics, High Energy Physics - Theory, Quantum Physics}, primaryclass = {cond-mat.mes-hall}, url = {https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.125.186101}, }`

- Piotr Kopszak, Marek Mozrzymas, Michał Studziński, and Michał Horodecki. Multiport based teleportation — transmission of a large amount of quantum information.
*Quantum 5, 576 (2021)*, aug 2020. doi:10.22331/q-2021-11-11-576

[BibTeX] [Abstract] [Download PDF]

We analyse the problem of transmitting a number of unknown quantum states or one composite system in one go. We derive a lower bound on the performance of such process, measured in the entanglement fidelity. The obtained bound is effectively computable and outperforms the explicit values of the entanglement fidelity calculated for the pre-existing variants of the port-based protocols, allowing for teleportation of a much larger amount of quantum information. The comparison with the exact formulas and similar analysis for the probabilistic scheme is also discussed. In particular, we present the closed-form expressions for the entanglement fidelity and for the probability of success in the probabilistic scheme in the qubit case in the picture of the spin angular momentum.

`@Article{Kopszak2020, author = {Piotr Kopszak and Marek Mozrzymas and Michał Studziński and Michał Horodecki}, journal = {Quantum 5, 576 (2021)}, title = {Multiport based teleportation -- transmission of a large amount of quantum information}, year = {2020}, month = aug, abstract = {We analyse the problem of transmitting a number of unknown quantum states or one composite system in one go. We derive a lower bound on the performance of such process, measured in the entanglement fidelity. The obtained bound is effectively computable and outperforms the explicit values of the entanglement fidelity calculated for the pre-existing variants of the port-based protocols, allowing for teleportation of a much larger amount of quantum information. The comparison with the exact formulas and similar analysis for the probabilistic scheme is also discussed. In particular, we present the closed-form expressions for the entanglement fidelity and for the probability of success in the probabilistic scheme in the qubit case in the picture of the spin angular momentum.}, archiveprefix = {arXiv}, doi = {10.22331/q-2021-11-11-576}, eprint = {2008.00856}, groups = {Michal_H}, keywords = {quant-ph}, primaryclass = {quant-ph}, url = {http://arxiv.org/pdf/2008.00856v3}, }`

### 2019

- Alejandro Pozas-Kerstjens, Rafael Rabelo, Łukasz Rudnicki, Rafael Chaves, Daniel Cavalcanti, Miguel Navascués, and Antonio Acín. Bounding the sets of classical and quantum correlations in networks.
*Physical Review Letters*, 123(14):140503, oct 2019. acknowledgment to ICTQT IRAP project included doi:10.1103/PhysRevLett.123.140503

[BibTeX] [Download PDF]`@Article{pozas-kerstjens_bounding_2019, author = {Pozas-Kerstjens, Alejandro and Rabelo, Rafael and Rudnicki, Łukasz and Chaves, Rafael and Cavalcanti, Daniel and Navascués, Miguel and Acín, Antonio}, journal = {Physical {R}eview {L}etters}, title = {Bounding the sets of classical and quantum correlations in networks}, year = {2019}, issn = {0031-9007, 1079-7114}, month = oct, number = {14}, pages = {140503}, volume = {123}, doi = {10.1103/PhysRevLett.123.140503}, groups = {Rudnicki}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.140503}, urldate = {2020-04-22}, note = {acknowledgment to ICTQT IRAP project included} }`

- Dong Yang, Karol Horodecki, and Andreas Winter. Distributed private randomness distillation.
*Physical Review Letters*, 123(17):170501, oct 2019. doi:10.1103/PhysRevLett.123.170501

[BibTeX] [Download PDF]`@Article{yang_distributed_2019, author = {Yang, Dong and Horodecki, Karol and Winter, Andreas}, journal = {Physical {R}eview {L}etters}, title = {Distributed private randomness distillation}, year = {2019}, issn = {0031-9007, 1079-7114}, month = oct, number = {17}, pages = {170501}, volume = {123}, doi = {10.1103/PhysRevLett.123.170501}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.170501}, urldate = {2020-04-22}, }`

- Thomas Van Himbeeck, Jonatan Bohr Brask, Stefano Pironio, Ravishankar Ramanathan, Ana Belén Sainz, and Elie Wolfe. Quantum violations in the Instrumental scenario and their relations to the Bell scenario.
*Quantum*, 3:186, sep 2019. doi:10.22331/q-2019-09-16-186

[BibTeX] [Abstract] [Download PDF]

The causal structure of any experiment implies restrictions on the observable correlations between measurement outcomes, which are different for experiments exploiting classical, quantum, or post-quantum resources. In the study of Bell nonlocality, these differences have been explored in great detail for more and more involved causal structures. Here, we go in the opposite direction and identify the simplest causal structure which exhibits a separation between classical, quantum, and post-quantum correlations. It arises in the so-called Instrumental scenario, known from classical causal models. We derive inequalities for this scenario and show that they are closely related to well-known Bell inequalities, such as the Clauser-Horne-Shimony-Holt inequality, which enables us to easily identify their classical, quantum, and post-quantum bounds as well as strategies violating the first two. The relations that we uncover imply that the quantum or post-quantum advantages witnessed by the violation of our Instrumental inequalities are not fundamentally different from those witnessed by the violations of standard inequalities in the usual Bell scenario. However, non-classical tests in the Instrumental scenario require fewer input choices than their Bell scenario counterpart, which may have potential implications for device-independent protocols.

`@Article{van_himbeeck_quantum_2019, author = {Van Himbeeck, Thomas and Bohr Brask, Jonatan and Pironio, Stefano and Ramanathan, Ravishankar and Sainz, Ana Belén and Wolfe, Elie}, journal = {Quantum}, title = {Quantum violations in the {Instrumental} scenario and their relations to the {Bell} scenario}, year = {2019}, issn = {2521-327X}, month = sep, pages = {186}, volume = {3}, abstract = {The causal structure of any experiment implies restrictions on the observable correlations between measurement outcomes, which are different for experiments exploiting classical, quantum, or post-quantum resources. In the study of Bell nonlocality, these differences have been explored in great detail for more and more involved causal structures. Here, we go in the opposite direction and identify the simplest causal structure which exhibits a separation between classical, quantum, and post-quantum correlations. It arises in the so-called Instrumental scenario, known from classical causal models. We derive inequalities for this scenario and show that they are closely related to well-known Bell inequalities, such as the Clauser-Horne-Shimony-Holt inequality, which enables us to easily identify their classical, quantum, and post-quantum bounds as well as strategies violating the first two. The relations that we uncover imply that the quantum or post-quantum advantages witnessed by the violation of our Instrumental inequalities are not fundamentally different from those witnessed by the violations of standard inequalities in the usual Bell scenario. However, non-classical tests in the Instrumental scenario require fewer input choices than their Bell scenario counterpart, which may have potential implications for device-independent protocols.}, doi = {10.22331/q-2019-09-16-186}, groups = {Belen}, language = {en}, url = {https://quantum-journal.org/papers/q-2019-09-16-186/}, urldate = {2020-04-22}, }`

- Piotr Mironowicz and Marcin Pawłowski. Experimentally feasible semi-device-independent certification of four-outcome positive-operator-valued measurements.
*Physical Review A*, 100(3):030301, sep 2019. doi:10.1103/PhysRevA.100.030301

[BibTeX] [Download PDF]`@Article{mironowicz_experimentally_2019, author = {Mironowicz, Piotr and Pawłowski, Marcin}, journal = {Physical {R}eview {A}}, title = {Experimentally feasible semi-device-independent certification of four-outcome positive-operator-valued measurements}, year = {2019}, issn = {2469-9926, 2469-9934}, month = sep, number = {3}, pages = {030301}, volume = {100}, doi = {10.1103/PhysRevA.100.030301}, groups = {Pawlowski}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.100.030301}, urldate = {2020-04-22} }`

- Robert Alicki. A quantum open system model of molecular battery charged by excitons.
*The Journal of Chemical Physics*, 150(21):214110, jun 2019. doi:10.1063/1.5096772

[BibTeX] [Download PDF]`@Article{alicki_quantum_2019, author = {Alicki, Robert}, journal = {The {J}ournal of {C}hemical {P}hysics}, title = {A quantum open system model of molecular battery charged by excitons}, year = {2019}, issn = {0021-9606}, month = jun, number = {21}, pages = {214110}, volume = {150}, doi = {10.1063/1.5096772}, url = {https://aip.scitation.org/doi/10.1063/1.5096772}, urldate = {2020-04-22}, }`

- Giuseppe Baio, Dariusz Chruściński, Paweł Horodecki, Antonino Messina, and Gniewomir Sarbicki. Bounds on the entanglement of two-qutrit systems from fixed marginals.
*Physical Review A*, 99(6):062312, jun 2019. doi:10.1103/PhysRevA.99.062312

[BibTeX] [Download PDF]`@Article{baio_bounds_2019, author = {Baio, Giuseppe and Chruściński, Dariusz and Horodecki, Paweł and Messina, Antonino and Sarbicki, Gniewomir}, journal = {Physical {R}eview {A}}, title = {Bounds on the entanglement of two-qutrit systems from fixed marginals}, year = {2019}, issn = {2469-9926, 2469-9934}, month = jun, number = {6}, pages = {062312}, volume = {99}, doi = {10.1103/PhysRevA.99.062312}, groups = {Pawel_H}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.062312}, urldate = {2020-04-22}, }`

- Robert Alicki. Quantum Features of Macroscopic Fields: Entropy and Dynamics.
*Entropy*, 21(7):705, jul 2019. doi:10.3390/e21070705

[BibTeX] [Abstract] [Download PDF]

Macroscopic fields such as electromagnetic, magnetohydrodynamic, acoustic or gravitational waves are usually described by classical wave equations with possible additional damping terms and coherent sources. The aim of this paper is to develop a complete macroscopic formalism including random/thermal sources, dissipation and random scattering of waves by environment. The proposed reduced state of the field combines averaged field with the two-point correlation function called single-particle density matrix. The evolution equation for the reduced state of the field is obtained by reduction of the generalized quasi-free dynamical semigroups describing irreversible evolution of bosonic quantum field and the definition of entropy for the reduced state of the field follows from the von Neumann entropy of quantum field states. The presented formalism can be applied, for example, to superradiance phenomena and allows unifying the Mueller and Jones calculi in polarization optics.

`@article{robert_alicki_quantum_2019, title = {Quantum {Features} of {Macroscopic} {Fields}: {Entropy} and {Dynamics}}, volume = {21}, issn = {1099-4300}, shorttitle = {Quantum {Features} of {Macroscopic} {Fields}}, url = {https://www.mdpi.com/1099-4300/21/7/705}, doi = {10.3390/e21070705}, abstract = {Macroscopic fields such as electromagnetic, magnetohydrodynamic, acoustic or gravitational waves are usually described by classical wave equations with possible additional damping terms and coherent sources. The aim of this paper is to develop a complete macroscopic formalism including random/thermal sources, dissipation and random scattering of waves by environment. The proposed reduced state of the field combines averaged field with the two-point correlation function called single-particle density matrix. The evolution equation for the reduced state of the field is obtained by reduction of the generalized quasi-free dynamical semigroups describing irreversible evolution of bosonic quantum field and the definition of entropy for the reduced state of the field follows from the von Neumann entropy of quantum field states. The presented formalism can be applied, for example, to superradiance phenomena and allows unifying the Mueller and Jones calculi in polarization optics.}, language = {en}, number = {7}, urldate = {2020-04-22}, journal = {Entropy}, author = {{Robert Alicki}}, month = jul, year = {2019}, pages = {705}, }`

- Paweł Horodecki and Ravishankar Ramanathan. The relativistic causality versus no-signaling paradigm for multi-party correlations.
*Nature Communications*, 10(1):1701, dec 2019. doi:10.1038/s41467-019-09505-2

[BibTeX] [Download PDF]`@Article{horodecki_relativistic_2019, author = {Horodecki, Paweł and Ramanathan, Ravishankar}, journal = {Nature {C}ommunications}, title = {The relativistic causality versus no-signaling paradigm for multi-party correlations}, year = {2019}, issn = {2041-1723}, month = dec, number = {1}, pages = {1701}, volume = {10}, doi = {10.1038/s41467-019-09505-2}, groups = {Pawel_H}, language = {en}, url = {http://www.nature.com/articles/s41467-019-09505-2}, urldate = {2020-04-22}, }`

- Junghee Ryu, Bianka Woloncewicz, Marcin Marciniak, Marcin Wieśniak, and Marek Żukowski. General mapping of multiqudit entanglement conditions to nonseparability indicators for quantum-optical fields.
*Physical Review Research*, 1(3):032041, dec 2019. doi:10.1103/PhysRevResearch.1.032041

[BibTeX] [Download PDF]`@Article{ryu_general_2019, author = {Ryu, Junghee and Woloncewicz, Bianka and Marciniak, Marcin and Wieśniak, Marcin and Żukowski, Marek}, journal = {Physical {R}eview {R}esearch}, title = {General mapping of multiqudit entanglement conditions to nonseparability indicators for quantum-optical fields}, year = {2019}, issn = {2643-1564}, month = dec, number = {3}, pages = {032041}, volume = {1}, doi = {10.1103/PhysRevResearch.1.032041}, groups = {Zukowski}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.1.032041}, urldate = {2020-05-13}, }`

- Waldemar Kłobus, Adam Burchardt, Adrian Kołodziejski, Mahasweta Pandit, Tamás Vértesi, Karol Życzkowski, and Wiesław Laskowski. k-uniform mixed states.
*Physical Review A*, 100(3):032112, sep 2019. doi:10.1103/PhysRevA.100.032112

[BibTeX] [Download PDF]`@Article{klobus_k_2019, author = {Kłobus, Waldemar and Burchardt, Adam and Kołodziejski, Adrian and Pandit, Mahasweta and Vértesi, Tamás and Życzkowski, Karol and Laskowski, Wiesław}, journal = {Physical {R}eview {A}}, title = {k-uniform mixed states}, year = {2019}, issn = {2469-9926, 2469-9934}, month = sep, number = {3}, pages = {032112}, volume = {100}, doi = {10.1103/PhysRevA.100.032112}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.100.032112}, urldate = {2021-05-10}, }`

- Máté. Farkas and Jędrzej Kaniewski. Self-testing mutually unbiased bases in the prepare-and-measure scenario.
*Physical Review A*, 99(3):032316, mar 2019. doi:10.1103/PhysRevA.99.032316

[BibTeX] [Download PDF]`@Article{farkas_self-testing_2019, author = {Farkas, Máté and Kaniewski, Jędrzej}, journal = {Physical {R}eview {A}}, title = {Self-testing mutually unbiased bases in the prepare-and-measure scenario}, year = {2019}, issn = {2469-9926, 2469-9934}, month = mar, number = {3}, pages = {032316}, volume = {99}, doi = {10.1103/PhysRevA.99.032316}, language = {en}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.032316}, urldate = {2021-05-10}, }`

- Waldemar Klobus, Adam Burchardt, Adrian Kolodziejski, Mahasweta Pandit, Tamas Vertesi, Karol Zyczkowski, and Wieslaw Laskowski. k-uniform mixed states.
*Physical Review A*, 100(3):032112, sep 2019. arXiv: 1906.01311 doi:10.1103/PhysRevA.100.032112

[BibTeX] [Abstract] [Download PDF]

We investigate the maximum purity that can be achieved by k-uniform mixed states of N parties. Such N-party states have the property that all their k-party reduced states are maximally mixed. A scheme to construct explicitly k-uniform states using a set of specific N-qubit Pauli matrices is proposed. We provide several different examples of such states and demonstrate that in some cases the state corresponds to a particular orthogonal array. The obtained states, despite being mixed, reveal strong non-classical properties such as genuine multipartite entanglement or violation of Bell inequalities.

`@Article{klobus_$k$-uniform_2019, author = {Klobus, Waldemar and Burchardt, Adam and Kolodziejski, Adrian and Pandit, Mahasweta and Vertesi, Tamas and Zyczkowski, Karol and Laskowski, Wieslaw}, journal = {Physical {R}eview {A}}, title = {k-uniform mixed states}, year = {2019}, issn = {2469-9926, 2469-9934}, month = sep, note = {arXiv: 1906.01311}, number = {3}, pages = {032112}, volume = {100}, abstract = {We investigate the maximum purity that can be achieved by k-uniform mixed states of N parties. Such N-party states have the property that all their k-party reduced states are maximally mixed. A scheme to construct explicitly k-uniform states using a set of specific N-qubit Pauli matrices is proposed. We provide several different examples of such states and demonstrate that in some cases the state corresponds to a particular orthogonal array. The obtained states, despite being mixed, reveal strong non-classical properties such as genuine multipartite entanglement or violation of Bell inequalities.}, doi = {10.1103/PhysRevA.100.032112}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/1906.01311}, urldate = {2021-07-28}, }`

- Antonio Mandarino, Karl Joulain, Melisa Domínguez Gómez, and Bruno Bellomo. Thermal transistor effect in quantum systems.
*Physcal Review Applied 16, 034026 (2021)*, feb 2019. doi:10.1103/PhysRevApplied.16.034026

[BibTeX] [Abstract] [Download PDF]

We study a quantum system composed of three interacting qubits, each coupled to a different thermal reservoir. We show how to engineer it in order to build a quantum device that is analogous to an electronic bipolar transistor. We outline how the interaction among the qubits plays a crucial role for the appearance of the effect, also linking it to the characteristics of system-bath interactions that govern the decoherence and dissipation mechanism of the system. By comparing with previous proposals, the model considered here extends the regime of parameters where the transistor effect shows up and its robustness with respect to small variations of the coupling parameters. Moreover, our model appears to be more realistic and directly connected in terms of potential implementations to feasible setups in the domain of quantum spin chains and molecular nanomagnets.

`@Article{Mandarino2019, author = {Antonio Mandarino and Karl Joulain and Melisa Domínguez Gómez and Bruno Bellomo}, journal = {Physcal {R}eview {A}pplied 16, 034026 (2021)}, title = {Thermal transistor effect in quantum systems}, year = {2019}, month = feb, abstract = {We study a quantum system composed of three interacting qubits, each coupled to a different thermal reservoir. We show how to engineer it in order to build a quantum device that is analogous to an electronic bipolar transistor. We outline how the interaction among the qubits plays a crucial role for the appearance of the effect, also linking it to the characteristics of system-bath interactions that govern the decoherence and dissipation mechanism of the system. By comparing with previous proposals, the model considered here extends the regime of parameters where the transistor effect shows up and its robustness with respect to small variations of the coupling parameters. Moreover, our model appears to be more realistic and directly connected in terms of potential implementations to feasible setups in the domain of quantum spin chains and molecular nanomagnets.}, archiveprefix = {arXiv}, doi = {10.1103/PhysRevApplied.16.034026}, eprint = {1902.01309}, file = {:Mandarino2019 - Thermal Transistor Effect in Quantum Systems.pdf:PDF}, groups = {Zukowski}, keywords = {quant-ph}, primaryclass = {quant-ph}, url = {https://journals.aps.org/prapplied/pdf/10.1103/PhysRevApplied.16.034026}, }`

### 2018

- Arijit Dutta, Tschang-Uh Nahm, Jinhyoung Lee, and Marek Żukowski. Geometric extension of Clauser–Horne inequality to more qubits.
*New Journal of Physics*, 20(9):093006, sep 2018. doi:10.1088/1367-2630/aadc78

[BibTeX] [Download PDF]`@Article{dutta_geometric_2018, author = {Dutta, Arijit and Nahm, Tschang-Uh and Lee, Jinhyoung and Żukowski, Marek}, journal = {New {J}ournal of {P}hysics}, title = {Geometric extension of {Clauser}–{Horne} inequality to more qubits}, year = {2018}, issn = {1367-2630}, month = sep, number = {9}, pages = {093006}, volume = {20}, doi = {10.1088/1367-2630/aadc78}, groups = {Zukowski}, url = {https://iopscience.iop.org/article/10.1088/1367-2630/aadc78}, urldate = {2020-04-22}, }`

## arXiv preprints

### 2022

- Markus Grassl, Anna-Lena Horlemann, and Violetta Weger. The Subfield Metric and its Application to Quantum Error Correction.
*arXiv:2212.00431 [cs.IT]*, dec 2022. arXiv:2212.00431 [cs.IT]

[BibTeX] [Download PDF]`@article{GrasslHorlemannWeger, title = {The Subfield Metric and its Application to Quantum Error Correction}, url = {https://arxiv.org/abs/2212.00431}, urldate = {2022-12-01}, abstract = {}, journal = {arXiv:2212.00431 [cs.IT]}, author = {Grassl, Markus and Horlemann, Anna-Lena and Weger, Violetta}, month = dec, year = {2022}, note = {arXiv:2212.00431 [cs.IT]}, keywords = {} }`

- Saverio Monaco, Oriel Kiss, Antonio Mandarino, Sofia Vallecorsa, and Michele Grossi. Quantum phase detection generalisation from marginal quantum neural network models. , 2022. doi:10.48550/ARXIV.2208.08748

[BibTeX] [Download PDF]`@article{QCNN_ANNNI, doi = {10.48550/ARXIV.2208.08748}, url = {https://arxiv.org/abs/2208.08748}, author = {Monaco, Saverio and Kiss, Oriel and Mandarino, Antonio and Vallecorsa, Sofia and Grossi, Michele}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Quantum phase detection generalisation from marginal quantum neural network models}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Michele Grossi, Oriel Kiss, Francesco De Luca, Carlo Zollo, Ian Gremese, and Antonio Mandarino. Finite-size criticality in fully connected spin models on superconducting quantum hardware. , 2022. doi:10.48550/ARXIV.2208.02731

[BibTeX] [Download PDF]`@article{VQE_LMG, doi = {10.48550/ARXIV.2208.02731}, url = {https://arxiv.org/abs/2208.02731}, author = {Grossi, Michele and Kiss, Oriel and De Luca, Francesco and Zollo, Carlo and Gremese, Ian and Mandarino, Antonio}, keywords = {Quantum Physics (quant-ph), Statistical Mechanics (cond-mat.stat-mech), FOS: Physical sciences, FOS: Physical sciences}, title = {Finite-size criticality in fully connected spin models on superconducting quantum hardware}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Łukasz Rudnicki, Waldemar Kłobus, Otavio A. D. Molitor, and Wiesław Laskowski. Salient signatures of entanglement in the surrounding environment. 2022. doi:10.48550/ARXIV.2209.05197

[BibTeX] [Download PDF]`@misc{https://doi.org/10.48550/arxiv.2209.05197, doi = {10.48550/ARXIV.2209.05197}, url = {https://arxiv.org/abs/2209.05197}, author = {Rudnicki, Łukasz and Kłobus, Waldemar and Molitor, Otavio A. D. and Laskowski, Wiesław}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Salient signatures of entanglement in the surrounding environment}, publisher = {arXiv}, year = {2022}, }`

- Fattah Sakuldee and Łukasz Rudnicki. When does an entanglement breaking channel break entanglement?. , 2022.

[BibTeX]`@article{https://doi.org/10.48550/arxiv.2209.08689, author = {Sakuldee, Fattah and Rudnicki, Łukasz}, title = {When does an entanglement breaking channel break entanglement?}, publisher = {arXiv}, year = {2022} }`

- Nikolai Miklin, Anubhav Chaturvedi, Mohamed Bourennane, Marcin Pawłowski, and Adán Cabello. Exponentially decreasing critical detection efficiency for any Bell inequality. 2022. doi:10.48550/ARXIV.2204.11726

[BibTeX] [Download PDF]`@misc{https://doi.org/10.48550/arxiv.2204.11726, doi = {10.48550/ARXIV.2204.11726}, url = {https://arxiv.org/abs/2204.11726}, author = {Miklin, Nikolai and Chaturvedi, Anubhav and Bourennane, Mohamed and Pawłowski, Marcin and Cabello, Adán}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Exponentially decreasing critical detection efficiency for any Bell inequality}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Ana Belén Sainz. Q-Turn: Changing Paradigms In Quantum Science.
*arXiv:2202.06867 [physics.soc-ph]*, 2022.

[BibTeX]`@article{sainz2022q_arXiv, title={Q-Turn: Changing Paradigms In Quantum Science}, author={Sainz, Ana Bel{\'e}n}, journal={arXiv:2202.06867 [physics.soc-ph]}, year={2022} }`

- Matty J. Hoban, Tom Drescher, and Ana Belén Sainz. A hierarchy of semidefinite programs for generalised Einstein-Podolsky-Rosen scenarios.
*arXiv:2208.09236 [quant-ph]*, 2022.

[BibTeX]`@article{hoban2022hierarchy, title={A hierarchy of semidefinite programs for generalised Einstein-Podolsky-Rosen scenarios}, author={Hoban, Matty J and Drescher, Tom and Sainz, Ana Bel{\'e}n}, journal={arXiv:2208.09236 [quant-ph]}, year={2022} }`

- Markus Grassl. New Quantum Codes from CSS Codes.
*arXiv:2208.05353 [quant-ph]*, aug 2022. arXiv:2208.05353 [quant-ph]

[BibTeX] [Download PDF]`@article{Grassl_2022_NewQECC, title = {New Quantum Codes from {CSS} Codes}, url = {https://arxiv.org/abs/2208.05353}, urldate = {2022-08-11}, abstract = {}, journal = {arXiv:2208.05353 [quant-ph]}, author = {Grassl, Markus}, month = aug, year = {2022}, note = {arXiv:2208.05353 [quant-ph]}, keywords = {} }`

- Gaojun Luo, Martianus Frederic Ezerman, Markus Grassl, and San Ling. How Much Entanglement Does a Quantum Code Need?.
*arXiv:2207.05647 [quant-ph]*, jul 2022. arXiv:2207.05647 [quant-ph]

[BibTeX] [Download PDF]`@article{LuoEtAl_2022_EAQECC, title = {How Much Entanglement Does a Quantum Code Need?}, url = {https://arxiv.org/abs/2207.05647}, urldate = {2022-07-12}, abstract = {}, journal = {arXiv:2207.05647 [quant-ph]}, author = {Luo, Gaojun and Ezerman, Martianus Frederic and Grassl, Markus and Ling, San}, month = jul, year = {2022}, note = {arXiv:2207.05647 [quant-ph]}, keywords = {} }`

- John H. Selby, Elie Wolfe, David Schmid, and Ana Belén Sainz. An open-source linear program for testing nonclassicality. , 2022. doi:10.48550/ARXIV.2204.11905

[BibTeX] [Download PDF]`@article{Selby_linear_program_contextuality, doi = {10.48550/ARXIV.2204.11905}, url = {https://arxiv.org/abs/2204.11905}, author = {Selby, John H. and Wolfe, Elie and Schmid, David and Sainz, Ana Belén}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {An open-source linear program for testing nonclassicality}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- John H. Selby, Maria E. Stasinou, Stefano Gogioso, and Bob Coecke. Time symmetry in quantum theories and beyond. , 2022. doi:10.48550/ARXIV.2209.07867

[BibTeX] [Download PDF]`@article{Selby_time_symmetry, doi = {10.48550/ARXIV.2209.07867}, url = {https://arxiv.org/abs/2209.07867}, author = {Selby, John H. and Stasinou, Maria E. and Gogioso, Stefano and Coecke, Bob}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Time symmetry in quantum theories and beyond}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Chenfeng Cao, Chao Zhang, Zipeng Wu, Markus Grassl, and Bei Zeng. Quantum variational learning for quantum error-correcting codes.
*arXiv:2204.03560 [quant-ph]*, apr 2022. arXiv:2204.03560 [quant-ph]

[BibTeX] [Download PDF]`@article{CaoEtAl_2022_VarQEC, title = {Quantum variational learning for quantum error-correcting codes}, url = {https://arxiv.org/abs/2204.03560}, urldate = {2022-04-07}, abstract = {}, journal = {arXiv:2204.03560 [quant-ph]}, author = {Cao, Chenfeng and Zhang, Chao and Wu, Zipeng and Grassl, Markus and Zeng, Bei}, month = apr, year = {2022}, note = {arXiv:2204.03560 [quant-ph]}, keywords = {} }`

- Gianlorenzo Massaro, Giovanni Scala, Milena D’Angelo, and Francesco V. Pepe. Comparative analysis of signal-to-noise ratio in correlation plenoptic imaging architectures. , jun 2022.

[BibTeX] [Abstract]

Correlation plenoptic imaging (CPI) is a scanning-free diffraction-limited 3D optical imaging technique exploiting the peculiar properties of correlated light sources. CPI has been further extended to samples of interest to microscopy, such as fluorescent or scattering objects, in a modified architecture named correlation light-field microscopy (CLM). Interestingly, experiments have shown that the noise performances of CLM are significantly improved over the original CPI scheme, leading to better images and faster acquisition. In this work, we provide a theoretical foundation to such advantage by investigating the properties of both the signal-to-noise and the signal-to-background ratios of CLM and the original CPI setup.

`@Article{Massaro2022, author = {Gianlorenzo Massaro and Giovanni Scala and Milena D'Angelo and Francesco V. Pepe}, title = {Comparative analysis of signal-to-noise ratio in correlation plenoptic imaging architectures}, year = {2022}, month = jun, abstract = {Correlation plenoptic imaging (CPI) is a scanning-free diffraction-limited 3D optical imaging technique exploiting the peculiar properties of correlated light sources. CPI has been further extended to samples of interest to microscopy, such as fluorescent or scattering objects, in a modified architecture named correlation light-field microscopy (CLM). Interestingly, experiments have shown that the noise performances of CLM are significantly improved over the original CPI scheme, leading to better images and faster acquisition. In this work, we provide a theoretical foundation to such advantage by investigating the properties of both the signal-to-noise and the signal-to-background ratios of CLM and the original CPI setup.}, archiveprefix = {arXiv}, eprint = {2206.13412}, file = {:http\://arxiv.org/pdf/2206.13412v1:PDF}, keywords = {physics.optics, quant-ph}, primaryclass = {physics.optics}, }`

- Vinicius P. Rossi, Matty J. Hoban, and Ana Belen Sainz. On characterising assemblages in Einstein-Podolsky-Rosen scenarios.
*arXiv:2202.05553 [quant-ph]*, feb 2022. arXiv:2202.05553 [quant-ph]

[BibTeX] [Abstract] [Download PDF]

Characterising non-classical quantum phenomena is crucial not only from a fundamental perspective, but also to better understand its capabilities for information processing and communication tasks. In this work, we focus on exploring the characterisation of Einstein-Podolsky-Rosen inference (a.k.a. steering): a signature of non-classicality manifested when one or more parties in a Bell scenario have their systems and measurements described by quantum theory, rather than being treated as black boxes. We propose a way of characterising common-cause assemblages from the correlations that arise when the trusted party performs tomographically-complete measurements on their share of the experiment, and discuss the advantages and challenges of this approach. Within this framework, we show that so-called almost quantum assemblages satisfy the principle of macroscopic noncontextuality, and demonstrate that a subset of almost quantum correlations recover almost quantum assemblages in this approach.

`@article{rossi_2022_characterising, title = {On characterising assemblages in {Einstein-Podolsky-Rosen} scenarios}, url = {https://arxiv.org/abs/2202.05553}, urldate = {2022-03-29}, abstract = {Characterising non-classical quantum phenomena is crucial not only from a fundamental perspective, but also to better understand its capabilities for information processing and communication tasks. In this work, we focus on exploring the characterisation of Einstein-Podolsky-Rosen inference (a.k.a. steering): a signature of non-classicality manifested when one or more parties in a Bell scenario have their systems and measurements described by quantum theory, rather than being treated as black boxes. We propose a way of characterising common-cause assemblages from the correlations that arise when the trusted party performs tomographically-complete measurements on their share of the experiment, and discuss the advantages and challenges of this approach. Within this framework, we show that so-called almost quantum assemblages satisfy the principle of macroscopic noncontextuality, and demonstrate that a subset of almost quantum correlations recover almost quantum assemblages in this approach.}, journal = {arXiv:2202.05553 [quant-ph]}, author = {Rossi, Vinicius P. and Hoban, Matty J. and Sainz, Ana Belen}, month = feb, year = {2022}, note = {arXiv:2202.05553 [quant-ph]}, keywords = {Quantum Physics} }`

- Lorenzo Catani, Matthew Leifer, David Schmid, and Robert W. Spekkens. Reply to “Comment on ‘Why interference phenomena do not capture the essence of quantum theory’ “. 2022. doi:10.48550/ARXIV.2207.11791

[BibTeX] [Download PDF]`@misc{catani2022reply, doi = {10.48550/ARXIV.2207.11791}, url = {https://arxiv.org/abs/2207.11791}, author = {Catani, Lorenzo and Leifer, Matthew and Schmid, David and Spekkens, Robert W.}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Reply to "Comment on 'Why interference phenomena do not capture the essence of quantum theory' "}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Ayan Patra, Rivu Gupta, Saptarshi Roy, Tamoghna Das, and Aditi Sen De. Quantum Dense Coding Network using Multimode Squeezed States of Light. , 2022. doi:10.48550/arXiv.2204.14147

[BibTeX] [Abstract] [Download PDF]

We present a framework of a multimode dense coding network with multiple senders and a single receiver using continuous variable systems. The protocol is scalable to arbitrary numbers of modes with the encoding being displacements while the decoding involves homodyne measurements of the modes after they are combined in a pairwise manner by a sequence of beam splitters, thereby exhibiting its potentiality to implement in laboratories with currently available resources. We compute the closed form expression of the dense coding capacity for the cases of two and three senders that involve sharing of three- and four-mode states respectively. The dense coding capacity is calculated with the constraint of fixed average energy transmission when the modes of the sender are transferred to the receiver after the encoding operation. In both the cases, we demonstrate the quantum advantage of the protocol using paradigmatic classes of three- and four-mode states. The quantum advantage increases with the increase in the amount of energy that is allowed to be transmitted from the senders to the receiver.

`@article{CVDC_2022, title = {Quantum Dense Coding Network using Multimode Squeezed States of Light}, doi = {10.48550/arXiv.2204.14147}, url = {https://doi.org/10.48550/arXiv.2204.14147}, abstract = {We present a framework of a multimode dense coding network with multiple senders and a single receiver using continuous variable systems. The protocol is scalable to arbitrary numbers of modes with the encoding being displacements while the decoding involves homodyne measurements of the modes after they are combined in a pairwise manner by a sequence of beam splitters, thereby exhibiting its potentiality to implement in laboratories with currently available resources. We compute the closed form expression of the dense coding capacity for the cases of two and three senders that involve sharing of three- and four-mode states respectively. The dense coding capacity is calculated with the constraint of fixed average energy transmission when the modes of the sender are transferred to the receiver after the encoding operation. In both the cases, we demonstrate the quantum advantage of the protocol using paradigmatic classes of three- and four-mode states. The quantum advantage increases with the increase in the amount of energy that is allowed to be transmitted from the senders to the receiver.}, author = {Ayan Patra and Rivu Gupta and Saptarshi Roy and Tamoghna Das and Aditi Sen De}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, publisher = {arXiv}, year = {2022}, urldate = {2022-04-29}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Lorenzo Catani, Matthew Leifer, Giovanni Scala, David Schmid, and Robert W. Spekkens. What is nonclassical about uncertainty relations?. , jul 2022.

[BibTeX] [Abstract]

Uncertainty relations express limits on the extent to which the outcomes of distinct measurements on a single state can be made jointly predictable. The existence of nontrivial uncertainty relations in quantum theory is generally considered to be a way in which it entails a departure from the classical worldview. However, this view is undermined by the fact that there exist operational theories which exhibit nontrivial uncertainty relations but which are consistent with the classical worldview insofar as they admit of a generalized-noncontextual ontological model. This prompts the question of what aspects of uncertainty relations, if any, cannot be realized in this way and so constitute evidence of genuine nonclassicality. We here consider uncertainty relations describing the tradeoff between the predictability of a pair of binary-outcome measurements (e.g., measurements of Pauli X and Pauli Z observables in quantum theory). We show that, for a class of theories satisfying a particular symmetry property, the functional form of this predictability tradeoff is constrained by noncontextuality to be below a linear curve. Because qubit quantum theory has the relevant symmetry property, the fact that it has a quadratic tradeoff between these predictabilities is a violation of this noncontextual bound, and therefore constitutes an example of how the functional form of an uncertainty relation can witness contextuality. We also deduce the implications for a selected group of operational foils to quantum theory and consider the generalization to three measurements.

`@Article{Catani2022, author = {Lorenzo Catani and Matthew Leifer and Giovanni Scala and David Schmid and Robert W. Spekkens}, title = {What is nonclassical about uncertainty relations?}, year = {2022}, month = jul, abstract = {Uncertainty relations express limits on the extent to which the outcomes of distinct measurements on a single state can be made jointly predictable. The existence of nontrivial uncertainty relations in quantum theory is generally considered to be a way in which it entails a departure from the classical worldview. However, this view is undermined by the fact that there exist operational theories which exhibit nontrivial uncertainty relations but which are consistent with the classical worldview insofar as they admit of a generalized-noncontextual ontological model. This prompts the question of what aspects of uncertainty relations, if any, cannot be realized in this way and so constitute evidence of genuine nonclassicality. We here consider uncertainty relations describing the tradeoff between the predictability of a pair of binary-outcome measurements (e.g., measurements of Pauli X and Pauli Z observables in quantum theory). We show that, for a class of theories satisfying a particular symmetry property, the functional form of this predictability tradeoff is constrained by noncontextuality to be below a linear curve. Because qubit quantum theory has the relevant symmetry property, the fact that it has a quadratic tradeoff between these predictabilities is a violation of this noncontextual bound, and therefore constitutes an example of how the functional form of an uncertainty relation can witness contextuality. We also deduce the implications for a selected group of operational foils to quantum theory and consider the generalization to three measurements.}, archiveprefix = {arXiv}, eprint = {2207.11779}, file = {:http\://arxiv.org/pdf/2207.11779v1:PDF}, keywords = {quant-ph}, primaryclass = {quant-ph}, }`

- Lorenzo Catani, Matthew Leifer, Giovanni Scala, David Schmid, and Robert W. Spekkens. What aspects of the phenomenology of interference witness nonclassicality?. , nov 2022.

[BibTeX] [Abstract]

Interference phenomena are often claimed to resist classical explanation. However, such claims are undermined by the fact that the specific aspects of the phenomenology upon which they are based can in fact be reproduced in a noncontextual ontological model [Catani et al. arXiv:2111.13727]. This raises the question of what other aspects of the phenomenology of interference do in fact resist classical explanation. We answer this question by demonstrating that the most basic quantum wave-particle duality relation, which expresses the precise trade-off between path distinguishability and fringe visibility, cannot be reproduced in any noncontextual model. We do this by showing that it is a specific type of uncertainty relation, and then leveraging a recent result establishing that noncontextuality restricts the functional form of this uncertainty relation [Catani et al. arXiv:2207.11779]. Finally, we discuss what sorts of interferometric experiment can demonstrate contextuality via the wave-particle duality relation.

`@Article{Catani2022a, author = {Lorenzo Catani and Matthew Leifer and Giovanni Scala and David Schmid and Robert W. Spekkens}, title = {What aspects of the phenomenology of interference witness nonclassicality?}, year = {2022}, month = nov, abstract = {Interference phenomena are often claimed to resist classical explanation. However, such claims are undermined by the fact that the specific aspects of the phenomenology upon which they are based can in fact be reproduced in a noncontextual ontological model [Catani et al. arXiv:2111.13727]. This raises the question of what other aspects of the phenomenology of interference do in fact resist classical explanation. We answer this question by demonstrating that the most basic quantum wave-particle duality relation, which expresses the precise trade-off between path distinguishability and fringe visibility, cannot be reproduced in any noncontextual model. We do this by showing that it is a specific type of uncertainty relation, and then leveraging a recent result establishing that noncontextuality restricts the functional form of this uncertainty relation [Catani et al. arXiv:2207.11779]. Finally, we discuss what sorts of interferometric experiment can demonstrate contextuality via the wave-particle duality relation.}, archiveprefix = {arXiv}, eprint = {2211.09850}, file = {:http\://arxiv.org/pdf/2211.09850v1:PDF}, keywords = {quant-ph}, primaryclass = {quant-ph}, }`

- Tomasz Linowski, Alexander Teretenkov, and Łukasz Rudnicki. Dissipative evolution of quantum Gaussian states.
*arXiv e-prints*, pages arXiv:2105.12644, 2022.

[BibTeX] [Abstract] [Download PDF]

The covariance matrix contains the complete information about the second-order expectation values of the mode quadratures (position and momentum operators) of the system. Due to its prominence in studies of continuous variable systems, most significantly Gaussian states, special emphasis is put on time evolution models that result in self-contained equations for the covariance matrix. So far, despite not being explicitly implied by this requirement, virtually all such models assume a so- called quadratic, or second-order case, in which the generator of the evolution is at most second-order in the mode quadratures. Here, we provide an explicit model of covariance matrix evolution of infinite order. Furthermore, we derive the solution, including stationary states, for a large subclass of proposed evolutions. Our findings challenge the contemporary understanding of covariance matrix dynamics and may give rise to new methods and improvements in quantum technologies employing continuous variable systems.

`@Article{Linowski2021a, author = {Linowski, Tomasz and Teretenkov, Alexander and Rudnicki, Łukasz}, journal = {arXiv e-prints}, title = {Dissipative evolution of quantum Gaussian states}, year = {2022}, pages = {arXiv:2105.12644}, abstract = {The covariance matrix contains the complete information about the second-order expectation values of the mode quadratures (position and momentum operators) of the system. Due to its prominence in studies of continuous variable systems, most significantly Gaussian states, special emphasis is put on time evolution models that result in self-contained equations for the covariance matrix. So far, despite not being explicitly implied by this requirement, virtually all such models assume a so- called quadratic, or second-order case, in which the generator of the evolution is at most second-order in the mode quadratures. Here, we provide an explicit model of covariance matrix evolution of infinite order. Furthermore, we derive the solution, including stationary states, for a large subclass of proposed evolutions. Our findings challenge the contemporary understanding of covariance matrix dynamics and may give rise to new methods and improvements in quantum technologies employing continuous variable systems.}, archiveprefix = {arXiv}, eid = {arXiv:2105.12644}, eprint = {2105.12644}, keywords = {Quantum {P}hysics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210512644L}, }`

- Konrad Schlichtholz, Antonio Mandarino, and Marek Żukowski. Bosonic fields in states with undefined particle numbers possess detectable non-contextuality features, plus more .
*arXiv e-prints*, pages arXiv.2205.09440, may 2022.

[BibTeX] [Abstract] [Download PDF]

Most of the paradoxical, for the classical intuition, features of quantum theory were formulated for situations which involve a fixed number of particles. While one can now find a formulation of Bell’s theorem for quantum fields, a Kochen-Specker-type reasoning is usually formulated for just one particle, or like in the case of Peres-Mermin square for two. A question emerges. Is it possible to formulate a contextuality proof for situation in which the numbers of particles are fundamentally undefined? We address this problem for bosonic fields. We introduce a representation of the su(2) algebra in terms of boson number states in two modes that allows us to assess nonclassicality of states of bosonic fields. As a figure of merit of a nonclassical behaviour we analyze first of all contextuality, and we show that the introduced observables are handy and efficient to reveal violation of local realism, and to formulate entanglement indicators. We construct a method which extends the Kochen-Specker contextuality to bosonic quantum fields. A form of an inequality is derived using a suitable version of the Peres-Mermin square. The entanglement indicators use a witness built with specially defined Pauli-like observables. Finally, Bell-nonclassicality is discussed: an inequality that involves the expectation values of pairs of the Pauli-like operators is presented. The introduced indicators are shown to be effective, e.g. they reveal nonclassicality in situaations involving undefined boson numbers. This is shown via quantum optical examples of the 2×2 bright squeezed vacuum state, and a recently discussed bright-GHZ state resulting from multiple three photon emissions in a parametric process.

`@Article{Schlichtholz2022, author = { Schlichtholz, Konrad and Mandarino, Antonio and Żukowski, Marek }, journal = {arXiv e-prints}, title = { Bosonic fields in states with undefined particle numbers possess detectable non-contextuality features, plus more }, year = {2022}, month = may, pages = {arXiv.2205.09440}, abstract = { Most of the paradoxical, for the classical intuition, features of quantum theory were formulated for situations which involve a fixed number of particles. While one can now find a formulation of Bell's theorem for quantum fields, a Kochen-Specker-type reasoning is usually formulated for just one particle, or like in the case of Peres-Mermin square for two. A question emerges. Is it possible to formulate a contextuality proof for situation in which the numbers of particles are fundamentally undefined? We address this problem for bosonic fields. We introduce a representation of the su(2) algebra in terms of boson number states in two modes that allows us to assess nonclassicality of states of bosonic fields. As a figure of merit of a nonclassical behaviour we analyze first of all contextuality, and we show that the introduced observables are handy and efficient to reveal violation of local realism, and to formulate entanglement indicators. We construct a method which extends the Kochen-Specker contextuality to bosonic quantum fields. A form of an inequality is derived using a suitable version of the Peres-Mermin square. The entanglement indicators use a witness built with specially defined Pauli-like observables. Finally, Bell-nonclassicality is discussed: an inequality that involves the expectation values of pairs of the Pauli-like operators is presented. The introduced indicators are shown to be effective, e.g. they reveal nonclassicality in situaations involving undefined boson numbers. This is shown via quantum optical examples of the 2×2 bright squeezed vacuum state, and a recently discussed bright-GHZ state resulting from multiple three photon emissions in a parametric process. }, archiveprefix = {arXiv}, eid = {arXiv.2205.09440}, eprint = {2205.09440}, keywords = {Quantum Physics, Physical sciences }, primaryclass = {quant-ph}, url = {https://arxiv.org/abs/2205.09440}, }`

- Tanmoy Biswas, Marcin Łobejko, Paweł Mazurek, Konrad Jałowiecki, and Michał Horodecki. Extraction of ergotropy: free energy bound and application to open cycle engines. , 2022. doi:10.48550/ARXIV.2205.06455

[BibTeX] [Download PDF]`@Article{https://doi.org/10.48550/arxiv.2205.06455, doi = {10.48550/ARXIV.2205.06455}, url = {https://arxiv.org/abs/2205.06455}, author = {Biswas, Tanmoy and Łobejko, Marcin and Mazurek, Paweł and Jałowiecki, Konrad and Horodecki, Michał}, keywords = {Quantum Physics (quant-ph), Statistical Mechanics (cond-mat.stat-mech), FOS: Physical sciences, FOS: Physical sciences}, title = {Extraction of ergotropy: free energy bound and application to open cycle engines}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Tomasz Linowski, Konrad Schlichtholz, and Łukasz Rudnicki. A formal relation between Pegg-Barnett and Paul quantum phase frameworks.
*arXiv e-prints*, pages arXiv.2205.09481, may 2022.

[BibTeX] [Abstract] [Download PDF]

The problem of defining a Hermitian quantum phase operator is nearly as old as quantum mechanics itself. Throughout the years, a number of solutions was proposed, ranging from abstract operator formalisms to phase-space methods. In this work, we connect two of the most prominent approaches: Pegg-Barnett and Paul formalisms, by proving that the Paul formalism is equivalent to the Pegg-Barnett formalism applied to an infinitely amplified state. Our findings fill in a conceptual gap in the understanding of the quantum phase problem.

`@Article{Linowski2022, author = {Linowski, Tomasz and Schlichtholz, Konrad and Rudnicki, Łukasz}, journal = {arXiv e-prints}, title = {A formal relation between Pegg-Barnett and Paul quantum phase frameworks}, year = {2022}, month = may, pages = {arXiv.2205.09481}, abstract = {The problem of defining a Hermitian quantum phase operator is nearly as old as quantum mechanics itself. Throughout the years, a number of solutions was proposed, ranging from abstract operator formalisms to phase-space methods. In this work, we connect two of the most prominent approaches: Pegg-Barnett and Paul formalisms, by proving that the Paul formalism is equivalent to the Pegg-Barnett formalism applied to an infinitely amplified state. Our findings fill in a conceptual gap in the understanding of the quantum phase problem.}, archiveprefix = {arXiv}, eid = {arXiv.2205.09481}, eprint = {2205.09481}, keywords = {Quantum Physics, Physical sciences}, primaryclass = {quant-ph}, url = {https://arxiv.org/abs/2205.09481}, }`

- Beata Zjawin, David Schmid, Matty J. Hoban, and Ana Belén Sainz. The resource theory of nonclassicality of channel assemblages.
*arXiv e-prints*, pages arXiv:2209.10177, sep 2022.

[BibTeX] [Abstract] [Download PDF]

When two parties, Alice and Bob, share correlated quantum systems and Alice performs local measurements, Alice’s updated description of Bob’s state can provide evidence of nonclassical correlations. This simple scenario, famously studied by Einstein, Podolsky and Rosen (EPR), can be modified by allowing Bob to also have a classical or quantum system as an input. In this case, Alice updates her knowledge of the channel (rather than the state) in Bob’s lab. In this paper, we provide a unified framework for studying the nonclassicality of various such generalizations of the EPR scenario. We do so using a resource theory wherein the free operations are local operations and shared randomness (LOSR). We derive a semidefinite program for studying the pre-order of EPR resources, and discover possible conversions between the latter. Moreover, we study conversions between post-quantum resources both analytically and numerically.

`@Article{Zjawin2022, author = {Zjawin, Beata and Schmid, David and Hoban, Matty J. and Sainz, Ana Belén}, journal = {arXiv e-prints}, title = {The resource theory of nonclassicality of channel assemblages}, year = {2022}, month = sep, pages = {arXiv:2209.10177}, abstract = {When two parties, Alice and Bob, share correlated quantum systems and Alice performs local measurements, Alice's updated description of Bob's state can provide evidence of nonclassical correlations. This simple scenario, famously studied by Einstein, Podolsky and Rosen (EPR), can be modified by allowing Bob to also have a classical or quantum system as an input. In this case, Alice updates her knowledge of the channel (rather than the state) in Bob's lab. In this paper, we provide a unified framework for studying the nonclassicality of various such generalizations of the EPR scenario. We do so using a resource theory wherein the free operations are local operations and shared randomness (LOSR). We derive a semidefinite program for studying the pre-order of EPR resources, and discover possible conversions between the latter. Moreover, we study conversions between post-quantum resources both analytically and numerically. }, archiveprefix = {arXiv}, eid = {arXiv:2209.10177}, eprint = {2209.10177}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://arxiv.org/abs/2209.10177}, }`

- K. Anjali, I. Reena, Sudha, B. G. Divyamani, H. S. Karthik, K. S. Mallesh, and Usha A. R. Devi. Geometric picture for SLOCC classification of pure permutation symmetric three-qubit states.
*arXiv:2208.03024 [quant-ph]*, aug 2022. arXiv:2208.03024

[BibTeX] [Abstract] [Download PDF]

The quantum steering ellipsoid inscribed inside the Bloch sphere offers an elegant geometric visualization of two-qubit states shared between Alice and Bob. The set of Bloch vectors of Bob’s qubit, steered by Alice via all possible local measurements on her qubit, constitutes the steering ellipsoid. The steering ellipsoids are shown to be effective in capturing quantum correlation properties, such as monogamy, exhibited by entangled multiqubit systems. We focus here on the canonical ellipsoids of two-qubit states realized by incorporating optimal local filtering operations by Alice and Bob on their respective qubits. Based on these canonical forms we show that the reduced two-qubit states drawn from pure entangled three-qubit permutation symmetric states, which are inequivalent under stochastic local operations and classcial communication (SLOCC), carry distinct geometric signatures. We provide detailed analysis of the SLOCC canonical forms and the associated steering ellipsoids of the reduced two-qubit states extracted from entangled three-qubit pure symmetric states: We arrive at (i) a prolate spheroid centered at the origin of the Bloch sphere — with longest semiaxis along the z-direction (symmetry axis of the spheroid) equal to 1 — in the case of pure symmetric three-qubit states constructed by permutation of 3 distinct spinors and (ii) an oblate spheroid centered at (0,0,1/2) inside the Bloch sphere, with fixed semiaxes lengths (1/Sqrt[2],\, 1/Sqrt[2],\, 1/2)), when the three-qubit pure state is constructed via symmetrization of 2 distinct spinors. We also explore volume monogamy relations formulated in terms of the volumes of the steering ellipsoids of the SLOCC inequivalent pure entangled three-qubit symmetric states..

`@article{anjali_geometricpicture_2022, title = {Geometric picture for SLOCC classification of pure permutation symmetric three-qubit states}, url = {https://doi.org/10.48550/arXiv.2208.03024}, abstract = {The quantum steering ellipsoid inscribed inside the Bloch sphere offers an elegant geometric visualization of two-qubit states shared between Alice and Bob. The set of Bloch vectors of Bob's qubit, steered by Alice via all possible local measurements on her qubit, constitutes the steering ellipsoid. The steering ellipsoids are shown to be effective in capturing quantum correlation properties, such as monogamy, exhibited by entangled multiqubit systems. We focus here on the canonical ellipsoids of two-qubit states realized by incorporating optimal local filtering operations by Alice and Bob on their respective qubits. Based on these canonical forms we show that the reduced two-qubit states drawn from pure entangled three-qubit permutation symmetric states, which are inequivalent under stochastic local operations and classcial communication (SLOCC), carry distinct geometric signatures. We provide detailed analysis of the SLOCC canonical forms and the associated steering ellipsoids of the reduced two-qubit states extracted from entangled three-qubit pure symmetric states: We arrive at (i) a prolate spheroid centered at the origin of the Bloch sphere -- with longest semiaxis along the z-direction (symmetry axis of the spheroid) equal to 1 -- in the case of pure symmetric three-qubit states constructed by permutation of 3 distinct spinors and (ii) an oblate spheroid centered at (0,0,1/2) inside the Bloch sphere, with fixed semiaxes lengths (1/Sqrt[2],\, 1/Sqrt[2],\, 1/2)), when the three-qubit pure state is constructed via symmetrization of 2 distinct spinors. We also explore volume monogamy relations formulated in terms of the volumes of the steering ellipsoids of the SLOCC inequivalent pure entangled three-qubit symmetric states..}, urldate = {}, journal = {arXiv:2208.03024 [quant-ph]}, author = {K Anjali and I Reena and Sudha and B G Divyamani and H S Karthik and K S Mallesh and A R Usha Devi}, month = aug, year = {2022}, note = {arXiv:2208.03024}, keywords = {Quantum Physics}, }`

- Michał Banacki, Ravishankar Ramanathan, and Paweł Horodecki. Multipartite channel assemblages.
*arXiv:2205.05033 [quant-ph]*, may 2022. acknowledgement for ICTQT IRAP included

[BibTeX] [Abstract] [Download PDF]

Motivated by the recent studies on post-quantum steering, we generalize the notion of bipartite channel steering by introducing the concept of multipartite no-signaling channel assemblages. We first show that beyond the bipartite case, the no-signaling and quantum descriptions of channel assemblages do not coincide. Using the Choi-Jamiołkowski isomorphism, we present a complete characterization of these classes of assemblages and use this characterization to provide sufficient conditions for extremality of quantum channel assemblages within the set of all no-signaling channel assemblages. Finally, we introduce and discuss a relaxed version of channel steering where only certain subsystems obey the no-signaling constraints. In this latter asymmetric scenario we show the possibility of certifying a perfect key bit that is secure against a general no-signaling eavesdropper.

`@Article{arxiv_banacki_multipartite_2022, author = {Banacki, Michał and Ramanathan, Ravishankar and Horodecki, Paweł}, journal = {arXiv:2205.05033 [quant-ph]}, title = {Multipartite channel assemblages}, note = {acknowledgement for ICTQT IRAP included}, year = {2022}, month = may, note = {arXiv: 2205.05033}, abstract = {Motivated by the recent studies on post-quantum steering, we generalize the notion of bipartite channel steering by introducing the concept of multipartite no-signaling channel assemblages. We first show that beyond the bipartite case, the no-signaling and quantum descriptions of channel assemblages do not coincide. Using the Choi-Jamiołkowski isomorphism, we present a complete characterization of these classes of assemblages and use this characterization to provide sufficient conditions for extremality of quantum channel assemblages within the set of all no-signaling channel assemblages. Finally, we introduce and discuss a relaxed version of channel steering where only certain subsystems obey the no-signaling constraints. In this latter asymmetric scenario we show the possibility of certifying a perfect key bit that is secure against a general no-signaling eavesdropper.}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {https://arxiv.org/abs/2205.05033}, }`

- Marcin Łobejko, Marek Winczewski, Gerardo Suárez, Robert Alicki, and Michał Horodecki. Towards reconciliation of completely positive open system dynamics with the equilibration postulate. , 2022. doi:10.48550/ARXIV.2204.00643

[BibTeX] [Download PDF]`@article{arXiv_Mean_Force_Hamiltonian, doi = {10.48550/ARXIV.2204.00643}, url = {https://arxiv.org/abs/2204.00643}, author = {Łobejko, Marcin and Winczewski, Marek and Suárez, Gerardo and Alicki, Robert and Horodecki, Michał}, keywords = {Quantum Physics (quant-ph), Statistical Mechanics (cond-mat.stat-mech), FOS: Physical sciences, FOS: Physical sciences}, title = {Towards reconciliation of completely positive open system dynamics with the equilibration postulate}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Pedro R. Dieguez, Vinicius F. Lisboa, and Roberto M. Serra. Thermal devices powered by generalized measurements with indefinite causal order.
*arXiv preprint arXiv:2205.14406*, 2022.

[BibTeX] [Abstract]

A quantum-controlled device may produce a scenario in which two general quantum operations can be performed in a such way that it is not possible to associate a definite order for the operations application. Such an indefinite causal order can be explored to produce nontrivial effects in quantum thermal devices. We investigate a measurement-powered thermal device that consists of generalized measurement channels with adjustable intensity parameters, where energy is exchanged with the apparatus in the form of work or heat. The measurement-based device can operate as a heat engine, a thermal accelerator, or a refrigerator, according to a measurement intensity setting. By employing a quantum switch of two measurement channels, we explore a thermal device fueled by an indefinite causal order. We also discuss how a coherent control over an indefinite causal order structure can change the operating regimes of the measurement-powered thermal device to produce an advantage when compared to a scenario with an incoherent control of the order switch.

`@article{dieguez2022thermal, title={Thermal devices powered by generalized measurements with indefinite causal order}, author={Dieguez, Pedro R and Lisboa, Vinicius F and Serra, Roberto M}, abstract={A quantum-controlled device may produce a scenario in which two general quantum operations can be performed in a such way that it is not possible to associate a definite order for the operations application. Such an indefinite causal order can be explored to produce nontrivial effects in quantum thermal devices. We investigate a measurement-powered thermal device that consists of generalized measurement channels with adjustable intensity parameters, where energy is exchanged with the apparatus in the form of work or heat. The measurement-based device can operate as a heat engine, a thermal accelerator, or a refrigerator, according to a measurement intensity setting. By employing a quantum switch of two measurement channels, we explore a thermal device fueled by an indefinite causal order. We also discuss how a coherent control over an indefinite causal order structure can change the operating regimes of the measurement-powered thermal device to produce an advantage when compared to a scenario with an incoherent control of the order switch.}, journal={arXiv preprint arXiv:2205.14406}, year={2022} }`

- Ismael L. Paiva, Pedro R. Dieguez, Renato M. Angelo, and Eliahu Cohen. Coherence and realism in the Aharonov-Bohm effect.
*arXiv preprint arXiv:2209.00480*, 2022.

[BibTeX] [Abstract]

The Aharonov-Bohm effect is a fundamental topological phenomenon with a wide range of applications. It consists of a charge encircling a region with a magnetic flux in a superposition of wavepackets having their relative phase affected by the flux. In this work, we analyze this effect using an entropic measure known as realism, originally introduced as a quantifier of a system’s degree of reality and mathematically related to notions of global and local quantum coherence. More precisely, we look for observables that lead to gauge-invariant realism associated with the charge before it completes its loop. We find that the realism of these operators has a sudden change when the line connecting the center of both wavepackets crosses the solenoid. Moreover, we consider the case of a quantized magnetic field source, pointing out similarities and differences between the two cases. Finally, we discuss the implications of these results to the understanding of the effect.

`@article{paiva2022coherence, title={Coherence and realism in the Aharonov-Bohm effect}, author={Paiva, Ismael L and Dieguez, Pedro R and Angelo, Renato M and Cohen, Eliahu}, abstract={The Aharonov-Bohm effect is a fundamental topological phenomenon with a wide range of applications. It consists of a charge encircling a region with a magnetic flux in a superposition of wavepackets having their relative phase affected by the flux. In this work, we analyze this effect using an entropic measure known as realism, originally introduced as a quantifier of a system's degree of reality and mathematically related to notions of global and local quantum coherence. More precisely, we look for observables that lead to gauge-invariant realism associated with the charge before it completes its loop. We find that the realism of these operators has a sudden change when the line connecting the center of both wavepackets crosses the solenoid. Moreover, we consider the case of a quantized magnetic field source, pointing out similarities and differences between the two cases. Finally, we discuss the implications of these results to the understanding of the effect.}, journal={arXiv preprint arXiv:2209.00480}, year={2022} }`

- RR Rodriguez, B. Ahmadi, G. Suarez, P. Mazurek, S. Barzanjeh, and P. Horodecki. Optimal Quantum Control of Charging Quantum Batteries.
*arXiv preprint arXiv:2207.00094*, 2022. acknowledgement for ICTQT IRAP included

[BibTeX]`@article{rodriguez2022optimal, title={Optimal Quantum Control of Charging Quantum Batteries}, author={Rodriguez, RR and Ahmadi, B and Suarez, G and Mazurek, P and Barzanjeh, S and Horodecki, P}, journal={arXiv preprint arXiv:2207.00094}, note= {acknowledgement for ICTQT IRAP included}, year={2022} }`

- Borhan Ahmadi, Pawel Mazurek, Ricard Ravell Rodriguez, Shabir Barzanjeh, Robert Alicki, and Pawel Horodecki. Catalysis in Charging Quantum Batteries.
*arXiv preprint arXiv:2205.05018*, 2022. acknowledgement for ICTQT IRAP included

[BibTeX]`@article{ahmadi2022catalysis, title={Catalysis in Charging Quantum Batteries}, author={Ahmadi, Borhan and Mazurek, Pawel and Rodriguez, Ricard Ravell and Barzanjeh, Shabir and Alicki, Robert and Horodecki, Pawel}, journal={arXiv preprint arXiv:2205.05018}, note= {acknowledgement for ICTQT IRAP included}, year={2022} }`

- Karol Horodecki, Jingfang Zhou, Maciej Stankiewicz, Roberto Salazar, Paweł Horodecki, Robert Raussendorf, Ryszard Horodecki, Ravishankar Ramanathan, and Emily Tyhurst. The rank of contextuality. , 2022. doi:10.48550/ARXIV.2205.10307

[BibTeX] [Download PDF]`@article{https://doi.org/10.48550/arxiv.2205.10307, doi = {10.48550/ARXIV.2205.10307}, url = {https://arxiv.org/abs/2205.10307}, author = {Horodecki, Karol and Zhou, Jingfang and Stankiewicz, Maciej and Salazar, Roberto and Horodecki, Paweł and Raussendorf, Robert and Horodecki, Ryszard and Ramanathan, Ravishankar and Tyhurst, Emily}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {The rank of contextuality}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Pawel Blasiak, Ewa Borsuk, and Marcin Markiewicz. Arbitrary entanglement of three qubits via linear optics.
*arXiv preprint arXiv:2202.01985*, 2022.

[BibTeX]`@article{Blasiak223QBits, title={Arbitrary entanglement of three qubits via linear optics}, author={Blasiak, Pawel and Borsuk, Ewa and Markiewicz, Marcin}, journal={arXiv preprint arXiv:2202.01985}, year={2022} }`

- Marcin Markiewicz and Janusz Przewocki. Duality of averaging of quantum states over arbitrary symmetry groups revealing Schur-Weyl duality.
*arXiv preprint arXiv:2208.076894*, 2022.

[BibTeX]`@article{Markiewicz22SLDFS, title={Duality of averaging of quantum states over arbitrary symmetry groups revealing {Schur-Weyl} duality}, author={Markiewicz, Marcin and Przewocki, Janusz}, journal={arXiv preprint arXiv:2208.076894}, year={2022} }`

- Jay Lawrence, Marcin Markiewicz, and Marek Żukowski. Relative facts do not exist. Relational Quantum Mechanics is Incompatible with Quantum Mechanics.
*arXiv preprint arXiv:2208.11793*, 2022.

[BibTeX]`@article{Lawrence22RQM, title={Relative facts do not exist. {Relational Quantum Mechanics is Incompatible with Quantum Mechanics}}, author={Lawrence, Jay and Markiewicz, Marcin and Żukowski, Marek}, journal={arXiv preprint arXiv:2208.11793}, year={2022} }`

- Daniel Ebler, Michał Horodecki, Marcin Marciniak, Tomasz Młynik, Marco Túlio Quintino, and Michał Studziński. Optimal universal quantum circuits for unitary complex conjugation. , 2022. doi:10.48550/ARXIV.2206.00107

[BibTeX] [Download PDF]`@article{arxiv-Ebler-Studzinski, doi = {10.48550/ARXIV.2206.00107}, url = {https://arxiv.org/abs/2206.00107}, author = {Ebler, Daniel and Horodecki, Michał and Marciniak, Marcin and Młynik, Tomasz and Quintino, Marco Túlio and Studziński, Michał}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Optimal universal quantum circuits for unitary complex conjugation}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Michał Oszmaniec, Michał Horodecki, and Nicholas Hunter-Jones. Saturation and recurrence of quantum complexity in random quantum circuits. , 2022. doi:10.48550/ARXIV.2205.09734

[BibTeX] [Download PDF]`@article{arxiv-Oszmaniec-Hunter, doi = {10.48550/ARXIV.2205.09734}, url = {https://arxiv.org/abs/2205.09734}, author = {Oszmaniec, Michał and Horodecki, Michał and Hunter-Jones, Nicholas}, keywords = {Quantum Physics (quant-ph), Strongly Correlated Electrons (cond-mat.str-el), High Energy Physics - Theory (hep-th), Mathematical Physics (math-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Saturation and recurrence of quantum complexity in random quantum circuits}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Róbert Trényi, Árpád Lukács, Paweł Horodecki, Ryszard Horodecki, Tamás Vértesi, and Géza Tóth. Multicopy metrology with many-particle quantum states.
*arXiv:2203.05538 [quant-ph]*, mar 2022. acknowledgement for ICTQT IRAP included

[BibTeX] [Download PDF]`@article{arxiv_Trenyi_Multicopy_2022, author = {Trényi, Róbert and Lukács, Árpád and Horodecki, Paweł and Horodecki, Ryszard and Vértesi, Tamás and Tóth, Géza}, journal = {arXiv:2203.05538 [quant-ph]}, title = {Multicopy metrology with many-particle quantum states}, note= {acknowledgement for ICTQT IRAP included}, year = {2022}, month = mar, note = {arXiv: 2203.05538}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {https://arxiv.org/abs/2203.05538}, }`

- Shuai Zhao, Ravishankar Ramanathan, Yuan Liu, and Paweł Horodecki. Tilted Hardy paradoxes for device-independent randomness extraction. , may 2022. acknowledgement for ICTQT IRAP included doi:10.48550/ARXIV.2205.02751

[BibTeX] [Download PDF]`@article{arxiv_Zhao_Tilted_2022, doi = {10.48550/ARXIV.2205.02751}, url = {https://arxiv.org/abs/2205.02751}, author = {Zhao, Shuai and Ramanathan, Ravishankar and Liu, Yuan and Horodecki, Paweł}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Tilted Hardy paradoxes for device-independent randomness extraction}, note= {acknowledgement for ICTQT IRAP included}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license}, month = may, note = {arXiv: 2205.02751}, groups = {Pawel_H}, }`

- Karol Horodecki, Jingfang Zhou, Maciej Stankiewicz, Roberto Salazar, Paweł Horodecki, Robert Raussendorf, Ryszard Horodecki, Ravishankar Ramanathan, and Emily Tyhurst. The rank of contextuality. , may 2022. acknowledgement for ICTQT IRAP included doi:10.48550/ARXIV.2205.10307

[BibTeX] [Download PDF]`@article{arxiv_Horodecki_The_2022, doi = {10.48550/ARXIV.2205.10307}, url = {https://arxiv.org/abs/2205.10307}, author = {Horodecki, Karol and Zhou, Jingfang and Stankiewicz, Maciej and Salazar, Roberto and Horodecki, Paweł and Raussendorf, Robert and Horodecki, Ryszard and Ramanathan, Ravishankar and Tyhurst, Emily}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {The rank of contextuality}, note= {acknowledgement for ICTQT IRAP included}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license}, month = may, note = {arXiv: 2205.10307}, groups = {Pawel_H}, }`

- Yuan Liu, Ravishankar Ramanathan, Karol Horodecki, Monika Rosicka, and Paweł Horodecki. Optimal Measurement Structures for Contextuality Applications. , jun 2022. acknowledgement for ICTQT IRAP included doi:10.48550/ARXIV.2206.13139

[BibTeX] [Download PDF]`@article{arxiv_Liu_Optimal_2022, doi = {10.48550/ARXIV.2206.13139}, url = {https://arxiv.org/abs/2206.13139}, author = {Liu, Yuan and Ramanathan, Ravishankar and Horodecki, Karol and Rosicka, Monika and Horodecki, Paweł}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Optimal Measurement Structures for Contextuality Applications}, note= {acknowledgement for ICTQT IRAP included}, publisher = {arXiv}, year = {2022}, copyright = {arXiv.org perpetual, non-exclusive license}, month = jun, note = {arXiv: 2206.13139}, groups = {Pawel_H}, }`

- Nitica Sakharwade, Michał Studzi’nski, Michał Eckstein, and Paweł Horodecki. Two instances of random access code in the quantum regime.
*arXiv preprint arXiv:2208.14422*, 2022. acknowledgement for ICTQT IRAP included

[BibTeX]`@article{sakharwade2022two, title={Two instances of random access code in the quantum regime}, author={Sakharwade, Nitica and Studzi{\'n}ski, Micha{\l} and Eckstein, Micha{\l} and Horodecki, Pawe{\l}}, journal={arXiv preprint arXiv:2208.14422}, note= {acknowledgement for ICTQT IRAP included}, year={2022} }`

- Ram Krishna Patra, Sahil Gopalkrishna Naik, Edwin Peter Lobo, Samrat Sen, Tamal Guha, Some Sankar Bhattacharya, Mir Alimuddin, and Manik Banik. *Classical superdense coding and communication advantage of a single quantum. , feb 2022. arXiv: 2202.06796 doi:10.48550/ARXIV.2202.06796

[BibTeX] [Download PDF]`@article{arxiv_Patra_Classical_2022, doi = {10.48550/ARXIV.2202.06796}, url = {https://arxiv.org/abs/2202.06796}, author = {Patra, Ram Krishna and Naik, Sahil Gopalkrishna and Lobo, Edwin Peter and Sen, Samrat and Guha, Tamal and Bhattacharya, Some Sankar and Alimuddin, Mir and Banik, Manik}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {*Classical superdense coding and communication advantage of a single quantum}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International}, month = feb, note = {arXiv: 2202.06796}, groups = {Pawel_H}, }`

- Marcin Wie’sniak Ekta Panwar Palash Pandya. An elegant proof of self-testing for multipartite Bell inequalities. , feb 2022. arXiv: 2202.06908 doi:10.48550/ARXIV.2202.06908

[BibTeX] [Download PDF]`@article{arxiv_Wiesniak_Self_Testing_2022, doi = {10.48550/ARXIV.2202.06908}, url = {https://arxiv.org/abs/2202.06908}, author = {Ekta Panwar, Palash Pandya, Marcin Wie\'sniak}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {An elegant proof of self-testing for multipartite Bell inequalities}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International}, month = feb, note = {arXiv: 2202.06908}, groups = {Marcin W.}, }`

- Marcin Wie’sniak Mirko Consiglio Tony John George Apollaro. A Variational Approach to the Quantum Separability Problem. , sep 2022. arXiv: 2209.01430 doi:10.48550/ARXIV.2209.01430

[BibTeX] [Download PDF]`@article{arxiv_Wiesniak_VSV_2022, doi = {10.48550/ARXIV.2209.01430}, url = {https://arxiv.org/abs/2209.01430}, author = {Mirko Consiglio, Tony John George Apollaro, Marcin Wie\'sniak}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {A Variational Approach to the Quantum Separability Problem}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International}, month = sep, note = {arXiv: 2209.01430}, groups = {Marcin W.}, }`

- Marcin Łobejko, Paweł Mazurek, and Michał Horodecki. The asymptotic emergence of the Second Law for a repeated charging process. 2022. doi:10.48550/ARXIV.2209.05339

[BibTeX] [Download PDF]`@misc{https://doi.org/10.48550/arxiv.2209.05339, doi = {10.48550/ARXIV.2209.05339}, url = {https://arxiv.org/abs/2209.05339}, author = {Łobejko, Marcin and Mazurek, Paweł and Horodecki, Michał}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {The asymptotic emergence of the Second Law for a repeated charging process}, publisher = {arXiv}, year = {2022}, copyright = {Creative Commons Attribution 4.0 International} }`

- Piotr Mironowicz. Quantum security and theory of decoherence.
*arXiv preprint arXiv:2205.12927*, 2022.

[BibTeX]`@article{mironowicz2022quantum, title={Quantum security and theory of decoherence}, author={Mironowicz, Piotr}, journal={arXiv preprint arXiv:2205.12927}, year={2022} }`

- Piotr Mironowicz. Entangled Rendezvous: A Possible Application of Bell Non-Locality For Mobile Agents on Networks.
*arXiv preprint arXiv:2207.14404*, 2022.

[BibTeX]`@article{mironowicz2022entangled, title={Entangled Rendezvous: A Possible Application of Bell Non-Locality For Mobile Agents on Networks}, author={Mironowicz, Piotr}, journal={arXiv preprint arXiv:2207.14404}, year={2022} }`

### 2021

- John H. Selby, David Schmid, Elie Wolfe, Ana Belén Sainz, Ravi Kunjwal, and Robert W. Spekkens. Contextuality without incompatibility. , 2021. doi:10.48550/ARXIV.2106.09045

[BibTeX] [Download PDF]`@article{Contextuality_without_incompatibility, doi = {10.48550/ARXIV.2106.09045}, url = {https://arxiv.org/abs/2106.09045}, author = {Selby, John H. and Schmid, David and Wolfe, Elie and Sainz, Ana Belén and Kunjwal, Ravi and Spekkens, Robert W.}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Contextuality without incompatibility}, publisher = {arXiv}, year = {2021}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Marcus Appleby, Ingemar Bengtsson, Markus Grassl, Michael Harrison, and Gary McConnell. SIC-POVMs from Stark Units.
*arXiv:2112.05552 [quant-ph]*, dec 2021. arXiv:2112.05552 [quant-ph]

[BibTeX] [Abstract] [Download PDF]

We propose a recipe for constructing a SIC fiducial vector in any complex Hilbert space whose dimension is of the form $d=n^2+3$, starting from Stark units in a ray class field that does not contain a complex root of unity. The recipe relies on some number theoretical theorems, a version of the Stark conjectures, and some standard conjectures for SICs. In this paper we focus on the conceptually simplest case, prime dimensions of the form $d=n^2+3$, and report that we have constructed SICs in twelve prime dimensions of this kind, the highest being $d=19603$.

`@article{Grassl_SIC-POVMS_2021, title = {{SIC-POVMs} from {Stark} Units}, url = {https://arxiv.org/abs/2112.05552}, urldate = {2021-12-13}, abstract = {We propose a recipe for constructing a SIC fiducial vector in any complex Hilbert space whose dimension is of the form $d=n^2+3$, starting from Stark units in a ray class field that does not contain a complex root of unity. The recipe relies on some number theoretical theorems, a version of the Stark conjectures, and some standard conjectures for SICs. In this paper we focus on the conceptually simplest case, prime dimensions of the form $d=n^2+3$, and report that we have constructed SICs in twelve prime dimensions of this kind, the highest being $d=19603$.}, journal = {arXiv:2112.05552 [quant-ph]}, author = {Appleby, Marcus and Bengtsson, Ingemar and Grassl, Markus and Harrison, Michael and McConnell, Gary}, month = dec, year = {2021}, note = {arXiv:2112.05552 [quant-ph]}, keywords = {Quantum Physics, Number Theory} }`

- John H. Selby, David Schmid, Elie Wolfe, Ana Belén Sainz, Ravi Kunjwal, and Robert W. Spekkens. Accessible fragments of generalized probabilistic theories, cone equivalence, and applications to witnessing nonclassicality.
*arXiv:2112.04521 [quant-ph]*, dec 2021. arXiv: 2112.04521

[BibTeX] [Abstract] [Download PDF]

The formalism of generalized probabilistic theories (GPTs) was originally developed as a way to characterize the landscape of conceivable physical theories. Thus, the GPT describing a given physical theory necessarily includes all physically possible processes. We here consider the question of how to provide a GPT-like characterization of a particular experimental setup within a given physical theory. We show that the resulting characterization is not generally a GPT in and of itself-rather, it is described by a more general mathematical object that we introduce and term an accessible GPT fragment. We then introduce an equivalence relation, termed cone equivalence, between accessible GPT fragments (and, as a special case, between standard GPTs). We give a number of examples of experimental scenarios that are best described using accessible GPT fragments, and where moreover cone-equivalence arises naturally. We then prove that an accessible GPT fragment admits of a classical explanation if and only if every other fragment that is cone-equivalent to it also admits of a classical explanation. Finally, we leverage this result to prove several fundamental results regarding the experimental requirements for witnessing the failure of generalized noncontextuality. In particular, we prove that neither incompatibility among measurements nor the assumption of freedom of choice is necessary for witnessing failures of generalized noncontextuality, and, moreover, that such failures can be witnessed even using arbitrarily inefficient detectors.

`@article{selby_accessible_2021, title = {Accessible fragments of generalized probabilistic theories, cone equivalence, and applications to witnessing nonclassicality}, url = {https://arxiv.org/abs/2112.04521}, abstract = {The formalism of generalized probabilistic theories (GPTs) was originally developed as a way to characterize the landscape of conceivable physical theories. Thus, the GPT describing a given physical theory necessarily includes all physically possible processes. We here consider the question of how to provide a GPT-like characterization of a particular experimental setup within a given physical theory. We show that the resulting characterization is not generally a GPT in and of itself-rather, it is described by a more general mathematical object that we introduce and term an accessible GPT fragment. We then introduce an equivalence relation, termed cone equivalence, between accessible GPT fragments (and, as a special case, between standard GPTs). We give a number of examples of experimental scenarios that are best described using accessible GPT fragments, and where moreover cone-equivalence arises naturally. We then prove that an accessible GPT fragment admits of a classical explanation if and only if every other fragment that is cone-equivalent to it also admits of a classical explanation. Finally, we leverage this result to prove several fundamental results regarding the experimental requirements for witnessing the failure of generalized noncontextuality. In particular, we prove that neither incompatibility among measurements nor the assumption of freedom of choice is necessary for witnessing failures of generalized noncontextuality, and, moreover, that such failures can be witnessed even using arbitrarily inefficient detectors.}, urldate = {2021-12-10}, journal = {arXiv:2112.04521 [quant-ph]}, author = {Selby, John H. and Schmid, David and Wolfe, Elie and Sainz, Ana Belén and Kunjwal, Ravi and Spekkens, Robert W.}, month = dec, year = {2021}, note = {arXiv: 2112.04521}, keywords = {Quantum Physics}, }`

- Lorenzo Catani, Matthew Leifer, David Schmid, and Robert W. Spekkens. Why interference phenomena do not capture the essence of quantum theory.
*arXiv:2111.13727 [quant-ph]*, nov 2021. arXiv: 2111.13727

[BibTeX] [Abstract] [Download PDF]

Quantum interference phenomena are widely viewed as posing a challenge to the classical worldview. Feynman even went so far as to proclaim that they are the only mystery and the basic peculiarity of quantum mechanics. Many have also argued that such phenomena force us to accept a number of radical interpretational conclusions, including: that a photon is neither a particle nor a wave but rather a schizophrenic sort of entity that toggles between the two possibilities, that reality is observer-dependent, and that systems either do not have properties prior to measurements or else have properties that are subject to nonlocal or backwards-in-time causal influences. In this work, we show that such conclusions are not, in fact, forced on us by the phenomena. We do so by describing an alternative to quantum theory, a statistical theory of a classical discrete field (the `toy field theory’) that reproduces the relevant phenomenology of quantum interference while rejecting these radical interpretational claims. It also reproduces a number of related interference experiments that are thought to support these interpretational claims, such as the Elitzur-Vaidman bomb tester, Wheeler’s delayed-choice experiment, and the quantum eraser experiment. The systems in the toy field theory are field modes, each of which possesses, at all times, both a particle-like property (a discrete occupation number) and a wave-like property (a discrete phase). Although these two properties are jointly possessed, the theory stipulates that they cannot be jointly known. The phenomenology that is generally cited in favour of nonlocal or backwards-in-time causal influences ends up being explained in terms of inferences about distant or past systems, and all that is observer-dependent is the observer’s knowledge of reality, not reality itself.

`@article{catani_why_2021, title = {Why interference phenomena do not capture the essence of quantum theory}, url = {http://arxiv.org/abs/2111.13727}, abstract = {Quantum interference phenomena are widely viewed as posing a challenge to the classical worldview. Feynman even went so far as to proclaim that they are the only mystery and the basic peculiarity of quantum mechanics. Many have also argued that such phenomena force us to accept a number of radical interpretational conclusions, including: that a photon is neither a particle nor a wave but rather a schizophrenic sort of entity that toggles between the two possibilities, that reality is observer-dependent, and that systems either do not have properties prior to measurements or else have properties that are subject to nonlocal or backwards-in-time causal influences. In this work, we show that such conclusions are not, in fact, forced on us by the phenomena. We do so by describing an alternative to quantum theory, a statistical theory of a classical discrete field (the `toy field theory') that reproduces the relevant phenomenology of quantum interference while rejecting these radical interpretational claims. It also reproduces a number of related interference experiments that are thought to support these interpretational claims, such as the Elitzur-Vaidman bomb tester, Wheeler's delayed-choice experiment, and the quantum eraser experiment. The systems in the toy field theory are field modes, each of which possesses, at all times, both a particle-like property (a discrete occupation number) and a wave-like property (a discrete phase). Although these two properties are jointly possessed, the theory stipulates that they cannot be jointly known. The phenomenology that is generally cited in favour of nonlocal or backwards-in-time causal influences ends up being explained in terms of inferences about distant or past systems, and all that is observer-dependent is the observer's knowledge of reality, not reality itself.}, urldate = {2021-11-30}, journal = {arXiv:2111.13727 [quant-ph]}, author = {Catani, Lorenzo and Leifer, Matthew and Schmid, David and Spekkens, Robert W.}, month = nov, year = {2021}, note = {arXiv: 2111.13727}, keywords = {Quantum Physics}, }`

- Robert Alicki and Alejandro Jenkins. Quantum thermodynamics of coronal heating.
*arXiv:2103.08746 [astro-ph, physics:physics, physics:quant-ph]*, may 2021. arXiv: 2103.08746

[BibTeX] [Abstract] [Download PDF]

Using the Markovian master equation for quantum quasiparticles, we show that convection in the stellar photosphere generates plasma waves by an irreversible process akin to Zeldovich superradiance and sonic booms. In the Sun, this mechanism is most efficient in quiet regions with magnetic fields of order one gauss. Most energy is carried by Alfven waves with megahertz frequencies, which travel upwards until they reach a height at which they dissipate via mode conversion. This gives the right power flux for the observed energy transport from the colder photosphere to the hotter corona.

`@article{alicki_quantum_2021, title = {Quantum thermodynamics of coronal heating}, url = {http://arxiv.org/abs/2103.08746}, abstract = {Using the Markovian master equation for quantum quasiparticles, we show that convection in the stellar photosphere generates plasma waves by an irreversible process akin to Zeldovich superradiance and sonic booms. In the Sun, this mechanism is most efficient in quiet regions with magnetic fields of order one gauss. Most energy is carried by Alfven waves with megahertz frequencies, which travel upwards until they reach a height at which they dissipate via mode conversion. This gives the right power flux for the observed energy transport from the colder photosphere to the hotter corona.}, urldate = {2021-07-28}, journal = {arXiv:2103.08746 [astro-ph, physics:physics, physics:quant-ph]}, author = {Alicki, Robert and Jenkins, Alejandro}, month = may, year = {2021}, note = {arXiv: 2103.08746}, keywords = {Astrophysics - Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Physics - Plasma Physics, Quantum Physics}, }`

- Pawel Blasiak, Ewa Borsuk, and Marcin Markiewicz. On safe post-selection for Bell nonlocality: Causal diagram approach.
*arXiv:2012.07285 [quant-ph]*, apr 2021. arXiv: 2012.07285

[BibTeX] [Abstract] [Download PDF]

Reasoning about Bell nonlocality from the correlations observed in post-selected data is always a matter of concern. This is because conditioning on the outcomes is a source of non-causal correlations, known as a selection bias, rising doubts whether the conclusion concerns the actual causal process or maybe it is just an effect of processing the data. Yet, even in the idealised case without detection inefficiencies, post-selection is an integral part of every experimental design, not least because it is a part of the entanglement generation process itself. In this paper we discuss a broad class of scenarios with post-selection on multiple spatially distributed outcomes. A simple criterion is worked out, called the all-but-one principle, showing when the conclusions about nonlocality from breaking Bell inequalities with post-selected data remain in force. Generality of this result, attained by adopting the high-level diagrammatic tools of causal inference, provides safe grounds for systematic reasoning based on the standard form of multipartite Bell inequalities in a wide array of entanglement generation schemes without worrying about the dangers of selection bias.

`@Article{blasiak_safe_2021, author = {Blasiak, Pawel and Borsuk, Ewa and Markiewicz, Marcin}, journal = {arXiv:2012.07285 [quant-ph]}, title = {On safe post-selection for {Bell} nonlocality: {Causal} diagram approach}, year = {2021}, month = apr, note = {arXiv: 2012.07285}, abstract = {Reasoning about Bell nonlocality from the correlations observed in post-selected data is always a matter of concern. This is because conditioning on the outcomes is a source of non-causal correlations, known as a selection bias, rising doubts whether the conclusion concerns the actual causal process or maybe it is just an effect of processing the data. Yet, even in the idealised case without detection inefficiencies, post-selection is an integral part of every experimental design, not least because it is a part of the entanglement generation process itself. In this paper we discuss a broad class of scenarios with post-selection on multiple spatially distributed outcomes. A simple criterion is worked out, called the all-but-one principle, showing when the conclusions about nonlocality from breaking Bell inequalities with post-selected data remain in force. Generality of this result, attained by adopting the high-level diagrammatic tools of causal inference, provides safe grounds for systematic reasoning based on the standard form of multipartite Bell inequalities in a wide array of entanglement generation schemes without worrying about the dangers of selection bias.}, keywords = {Quantum Physics}, shorttitle = {On safe post-selection for {Bell} nonlocality}, url = {http://arxiv.org/abs/2012.07285}, urldate = {2021-07-28}, }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Żukowski. No-go for device independent protocols with Tan-Walls-Collett `nonlocality of a single photon’.
*arXiv:2102.03254 [quant-ph]*, feb 2021. arXiv: 2102.03254

[BibTeX] [Abstract] [Download PDF]

We investigate the interferometric scheme put forward by Tan, Walls and Collett [Phys. Rev. Lett. \\textbackslashbf 66\, 256 (1991)] that aims to reveal Bell non-classicality of a single photon. By providing a local hidden variable model that reproduces their results, we decisively refute this claim. In particular, this means that the scheme cannot be used in device-independent protocols.

`@article{das_no-go_2021, title = {No-go for device independent protocols with {Tan}-{Walls}-{Collett} `nonlocality of a single photon'}, url = {http://arxiv.org/abs/2102.03254}, abstract = {We investigate the interferometric scheme put forward by Tan, Walls and Collett [Phys. Rev. Lett. \{{\textbackslash}bf 66\}, 256 (1991)] that aims to reveal Bell non-classicality of a single photon. By providing a local hidden variable model that reproduces their results, we decisively refute this claim. In particular, this means that the scheme cannot be used in device-independent protocols.}, urldate = {2021-07-28}, journal = {arXiv:2102.03254 [quant-ph]}, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Żukowski, Marek}, month = feb, year = {2021}, note = {arXiv: 2102.03254}, keywords = {Quantum Physics}, }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Zukowski. Can single photon excitation of two spatially separated modes lead to a violation of Bell inequality via homodyne measurements?.
*arXiv:2102.06689 [quant-ph]*, feb 2021. arXiv: 2102.06689

[BibTeX] [Abstract] [Download PDF]

We reconsider the all-optical homodyne-measurement based experimental schemes that aim to reveal Bell nonclassicality of a single photon, often termed `nonlocality’. We focus on the schemes put forward by Tan, Walls and Collett (TWC, 1991) and Hardy (1994). In the light of our previous work the Tan, Walls and Collett setup can be described by a precise local hidden variable model, hence the claimed nonclassicality of this proposal is apparent, whereas the nonclassicality proof proposed by Hardy is impeccable. In this work we resolve the following problem: which feature of the Hardy’s approach is crucial for its successful confirmation of nonclassicality. The scheme of Hardy differs from the Tan, Walls and Collett setup in two aspects. (i) It introduces a superposition of a single photon excitation with vacuum as the initial state of one of the input modes of a 50-50 beamsplitter, which creates the superposition state of two separable (exit) modes under investigation. (ii) In the final measurements Hardy’s proposal utilises a varying strengths of the local oscillator fields, whereas in the TWC case they are constant. In fact the local oscillators in Hardy’s scheme are either on or off (the local setting is specified by the presence or absence of the local auxiliary field). We show that it is the varying strength of the local oscillators, from setting to setting, which is the crucial feature enabling violation of local realism in the Hardy setup, whereas it is not necessary to use initial superposition of a single photon excitation with vacuum as the initial state of the input mode. Neither one needs to operate in the fully on/off detection scheme. Despite the failure of the Tan, Walls and Collett scheme in proving Bell nonclassicality, we show that their scheme can serve as an entanglement indicator.

`@article{das_can_2021, title = {Can single photon excitation of two spatially separated modes lead to a violation of {Bell} inequality via homodyne measurements?}, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Zukowski, Marek}, url = {http://arxiv.org/abs/2102.06689}, abstract = {We reconsider the all-optical homodyne-measurement based experimental schemes that aim to reveal Bell nonclassicality of a single photon, often termed `nonlocality'. We focus on the schemes put forward by Tan, Walls and Collett (TWC, 1991) and Hardy (1994). In the light of our previous work the Tan, Walls and Collett setup can be described by a precise local hidden variable model, hence the claimed nonclassicality of this proposal is apparent, whereas the nonclassicality proof proposed by Hardy is impeccable. In this work we resolve the following problem: which feature of the Hardy's approach is crucial for its successful confirmation of nonclassicality. The scheme of Hardy differs from the Tan, Walls and Collett setup in two aspects. (i) It introduces a superposition of a single photon excitation with vacuum as the initial state of one of the input modes of a 50-50 beamsplitter, which creates the superposition state of two separable (exit) modes under investigation. (ii) In the final measurements Hardy's proposal utilises a varying strengths of the local oscillator fields, whereas in the TWC case they are constant. In fact the local oscillators in Hardy's scheme are either on or off (the local setting is specified by the presence or absence of the local auxiliary field). We show that it is the varying strength of the local oscillators, from setting to setting, which is the crucial feature enabling violation of local realism in the Hardy setup, whereas it is not necessary to use initial superposition of a single photon excitation with vacuum as the initial state of the input mode. Neither one needs to operate in the fully on/off detection scheme. Despite the failure of the Tan, Walls and Collett scheme in proving Bell nonclassicality, we show that their scheme can serve as an entanglement indicator.}, urldate = {2021-07-28}, journal = {arXiv:2102.06689 [quant-ph]}, month = feb, year = {2021}, note = {arXiv: 2102.06689}, keywords = {Quantum Physics}, }`

- Pawel Blasiak, Ewa Borsuk, Marcin Markiewicz, and Yong-Su Kim. Efficient linear optical generation of a multipartite W state.
*arXiv:2103.02206 [quant-ph]*, mar 2021. arXiv: 2103.02206

[BibTeX] [Abstract] [Download PDF]

A novel scheme is presented for generation of a multipartite W state for arbitrary number of qubits. Based on a recent proposal of entanglement without touching, it serves to demonstrate the potential of particle indistinguishability as a useful resource of entanglement for practical applications. The devised scheme is efficient in design, meaning that it is built with linear optics without the need for auxiliary particles nor measurements. Yet, the success probability is shown to be highly competitive compared with the existing proposals (i.e. decreases polynomially with the number of qubits) and remains insensitive to particle statistics (i.e. has the same efficiency for bosons and fermions).

`@Article{blasiak_efficient_2021, author = {Blasiak, Pawel and Borsuk, Ewa and Markiewicz, Marcin and Kim, Yong-Su}, journal = {arXiv:2103.02206 [quant-ph]}, title = {Efficient linear optical generation of a multipartite {W} state}, year = {2021}, month = mar, note = {arXiv: 2103.02206}, abstract = {A novel scheme is presented for generation of a multipartite W state for arbitrary number of qubits. Based on a recent proposal of entanglement without touching, it serves to demonstrate the potential of particle indistinguishability as a useful resource of entanglement for practical applications. The devised scheme is efficient in design, meaning that it is built with linear optics without the need for auxiliary particles nor measurements. Yet, the success probability is shown to be highly competitive compared with the existing proposals (i.e. decreases polynomially with the number of qubits) and remains insensitive to particle statistics (i.e. has the same efficiency for bosons and fermions).}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2103.02206}, urldate = {2021-07-28}, }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, Bianka Woloncewicz, and Marek Żukowski. On detecting violation of local realism with photon-number resolving weak-field homodyne measurements.
*arXiv:2104.10703 [quant-ph]*, apr 2021. arXiv: 2104.10703

[BibTeX] [Abstract] [Download PDF]

Non-existence of a local hidden variables (LHV) model for a phenomenon benchmarks its use in device-independent quantum protocols. Nowadays photon-number resolving weak-field homodyne measurements allow realization of emblematic gedanken experiments. Alas, claims that we can have no LHV models for such experiments on (a) excitation of a pair of spatial modes by a single photon, and (b) two spatial modes in a weakly squeezed vacuum state, involving constant local oscillator strengths, are unfounded. For (a) an exact LHV model resolves the dispute on the “non-locality of a single photon” in its original formulation. It is measurements with local oscillators on or off that do not have LHV models.

`@article{das_detecting_2021, title = {On detecting violation of local realism with photon-number resolving weak-field homodyne measurements}, url = {http://arxiv.org/abs/2104.10703}, abstract = {Non-existence of a local hidden variables (LHV) model for a phenomenon benchmarks its use in device-independent quantum protocols. Nowadays photon-number resolving weak-field homodyne measurements allow realization of emblematic gedanken experiments. Alas, claims that we can have no LHV models for such experiments on (a) excitation of a pair of spatial modes by a single photon, and (b) two spatial modes in a weakly squeezed vacuum state, involving constant local oscillator strengths, are unfounded. For (a) an exact LHV model resolves the dispute on the "non-locality of a single photon" in its original formulation. It is measurements with local oscillators on or off that do not have LHV models.}, urldate = {2021-07-28}, journal = {arXiv:2104.10703 [quant-ph]}, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Żukowski, Marek}, month = apr, year = {2021}, note = {arXiv: 2104.10703}, keywords = {Quantum Physics}, }`

- Mariami Gachechiladze, Bartłomiej Bąk, Marcin Pawłowski, and Nikolai Miklin. Quantum Bell inequalities from Information Causality — tight for Macroscopic Locality.
*arXiv:2103.05029 [quant-ph]*, mar 2021. arXiv: 2103.05029

[BibTeX] [Abstract] [Download PDF]

Quantum generalizations of Bell inequalities are analytical expressions of correlations observed in the Bell experiment that are used to explain or estimate the set of correlations that quantum theory allows. Unlike standard Bell inequalities, their quantum analogs are rare in the literature, as no known algorithm can be used to find them systematically. In this work, we present a family of quantum Bell inequalities in scenarios where the number of settings or outcomes can be arbitrarily high. We derive these inequalities from the principle of Information Causality, and thus, we do not assume the formalism of quantum mechanics. Considering the symmetries of the derived inequalities, we show that the latter give the necessary and sufficient condition for the correlations to comply with Macroscopic Locality. As a result, we conclude that the principle of Information Causality is strictly stronger than the principle of Macroscopic Locality in the subspace defined by these symmetries.

`@article{gachechiladze_quantum_2021, title = {Quantum {Bell} inequalities from {Information} {Causality} -- tight for {Macroscopic} {Locality}}, url = {http://arxiv.org/abs/2103.05029}, abstract = {Quantum generalizations of Bell inequalities are analytical expressions of correlations observed in the Bell experiment that are used to explain or estimate the set of correlations that quantum theory allows. Unlike standard Bell inequalities, their quantum analogs are rare in the literature, as no known algorithm can be used to find them systematically. In this work, we present a family of quantum Bell inequalities in scenarios where the number of settings or outcomes can be arbitrarily high. We derive these inequalities from the principle of Information Causality, and thus, we do not assume the formalism of quantum mechanics. Considering the symmetries of the derived inequalities, we show that the latter give the necessary and sufficient condition for the correlations to comply with Macroscopic Locality. As a result, we conclude that the principle of Information Causality is strictly stronger than the principle of Macroscopic Locality in the subspace defined by these symmetries.}, urldate = {2021-07-28}, journal = {arXiv:2103.05029 [quant-ph]}, author = {Gachechiladze, Mariami and Bąk, Bartłomiej and Pawłowski, Marcin and Miklin, Nikolai}, month = mar, year = {2021}, note = {arXiv: 2103.05029}, keywords = {Quantum Physics}, }`

- David Schmid, John H. Selby, and Robert W. Spekkens. Unscrambling the omelette of causation and inference: The framework of causal-inferential theories.
*arXiv:2009.03297 [quant-ph]*, may 2021. arXiv: 2009.03297

[BibTeX] [Abstract] [Download PDF]

Using a process-theoretic formalism, we introduce the notion of a causal-inferential theory: a triple consisting of a theory of causal influences, a theory of inferences (of both the Boolean and Bayesian varieties), and a specification of how these interact. Recasting the notions of operational and realist theories in this mold clarifies what a realist account of an experiment offers beyond an operational account. It also yields a novel characterization of the assumptions and implications of standard no-go theorems for realist representations of operational quantum theory, namely, those based on Bell’s notion of locality and those based on generalized noncontextuality. Moreover, our process-theoretic characterization of generalised noncontextuality is shown to be implied by an even more natural principle which we term Leibnizianity. Most strikingly, our framework offers a way forward in a research program that seeks to circumvent these no-go results. Specifically, we argue that if one can identify axioms for a realist causal-inferential theory such that the notions of causation and inference can differ from their conventional (classical) interpretations, then one has the means of defining an intrinsically quantum notion of realism, and thereby a realist representation of operational quantum theory that salvages the spirit of locality and of noncontextuality.

`@article{schmid_unscrambling_2021, title = {Unscrambling the omelette of causation and inference: {The} framework of causal-inferential theories}, shorttitle = {Unscrambling the omelette of causation and inference}, url = {http://arxiv.org/abs/2009.03297}, abstract = {Using a process-theoretic formalism, we introduce the notion of a causal-inferential theory: a triple consisting of a theory of causal influences, a theory of inferences (of both the Boolean and Bayesian varieties), and a specification of how these interact. Recasting the notions of operational and realist theories in this mold clarifies what a realist account of an experiment offers beyond an operational account. It also yields a novel characterization of the assumptions and implications of standard no-go theorems for realist representations of operational quantum theory, namely, those based on Bell's notion of locality and those based on generalized noncontextuality. Moreover, our process-theoretic characterization of generalised noncontextuality is shown to be implied by an even more natural principle which we term Leibnizianity. Most strikingly, our framework offers a way forward in a research program that seeks to circumvent these no-go results. Specifically, we argue that if one can identify axioms for a realist causal-inferential theory such that the notions of causation and inference can differ from their conventional (classical) interpretations, then one has the means of defining an intrinsically quantum notion of realism, and thereby a realist representation of operational quantum theory that salvages the spirit of locality and of noncontextuality.}, urldate = {2021-07-28}, journal = {arXiv:2009.03297 [quant-ph]}, author = {Schmid, David and Selby, John H. and Spekkens, Robert W.}, month = may, year = {2021}, note = {arXiv: 2009.03297}, keywords = {Quantum Physics}, }`

- John H. Selby, Ana Belén Sainz, and Paweł Horodecki. Revisiting dynamics of quantum causal structures — when can causal order evolve?.
*arXiv:2008.12757 [quant-ph]*, mar 2021. arXiv: 2008.12757

[BibTeX] [Abstract] [Download PDF]

Recently, there has been substantial interest in studying the dynamics of quantum theory beyond that of states, in particular, the dynamics of channels, measurements, and higher-order transformations. Ref. [Phys. Rev. X 8(1), 011047 (2018)] pursues this using the process matrix formalism, together with a definition of the possible dynamics of such process matrices, and focusing especially on the question of evolution of causal structures. One of its major conclusions is a strong theorem saying that, within the formalism, under continuous and reversible transformations, the causal order between operations must be preserved. Here we find a surprising result: if one is to take into account a full picture of the physical evolution of operations within the standard quantum-mechanical formalism, then one can actually draw the opposite conclusion. That is, we show that under certain continuous and reversible dynamics the causal order between operations is not necessarily preserved. We moreover identify and analyse the root of this apparent contradiction, specifically, that the commonly accepted and widely applied framework of higher-order processes, whilst mathematically sound, is not always appropriate for drawing conclusions on the fundamentals of physical dynamics. Finally we show how to reconcile the elements of the whole picture following the intuition based on entanglement processing by local operations and classical communication.

`@Article{selby_revisiting_2021, author = {Selby, John H. and Sainz, Ana Belén and Horodecki, Paweł}, journal = {arXiv:2008.12757 [quant-ph]}, title = {Revisiting dynamics of quantum causal structures -- when can causal order evolve?}, year = {2021}, month = mar, note = {arXiv: 2008.12757}, abstract = {Recently, there has been substantial interest in studying the dynamics of quantum theory beyond that of states, in particular, the dynamics of channels, measurements, and higher-order transformations. Ref. [Phys. Rev. X 8(1), 011047 (2018)] pursues this using the process matrix formalism, together with a definition of the possible dynamics of such process matrices, and focusing especially on the question of evolution of causal structures. One of its major conclusions is a strong theorem saying that, within the formalism, under continuous and reversible transformations, the causal order between operations must be preserved. Here we find a surprising result: if one is to take into account a full picture of the physical evolution of operations within the standard quantum-mechanical formalism, then one can actually draw the opposite conclusion. That is, we show that under certain continuous and reversible dynamics the causal order between operations is not necessarily preserved. We moreover identify and analyse the root of this apparent contradiction, specifically, that the commonly accepted and widely applied framework of higher-order processes, whilst mathematically sound, is not always appropriate for drawing conclusions on the fundamentals of physical dynamics. Finally we show how to reconcile the elements of the whole picture following the intuition based on entanglement processing by local operations and classical communication.}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2008.12757}, urldate = {2021-07-28}, }`

- David Schmid, Thomas C. Fraser, Ravi Kunjwal, Ana Belen Sainz, Elie Wolfe, and Robert W. Spekkens. Understanding the interplay of entanglement and nonlocality: motivating and developing a new branch of entanglement theory.
*arXiv:2004.09194 [quant-ph]*, may 2021. arXiv: 2004.09194

[BibTeX] [Abstract] [Download PDF]

A standard approach to quantifying resources is to determine which operations on the resources are freely available, and to deduce the partial order over resources that is induced by the relation of convertibility under the free operations. If the resource of interest is the nonclassicality of the correlations embodied in a quantum state, i.e., entanglement, then the common assumption is that the appropriate choice of free operations is Local Operations and Classical Communication (LOCC). We here advocate for the study of a different choice of free operations, namely, Local Operations and Shared Randomness (LOSR), and demonstrate its utility in understanding the interplay between the entanglement of states and the nonlocality of the correlations in Bell experiments. Specifically, we show that the LOSR paradigm (i) provides a resolution of the anomalies of nonlocality, wherein partially entangled states exhibit more nonlocality than maximally entangled states, (ii) entails new notions of genuine multipartite entanglement and nonlocality that are free of the pathological features of the conventional notions, and (iii) makes possible a resource-theoretic account of the self-testing of entangled states which generalizes and simplifies prior results. Along the way, we derive some fundamental results concerning the necessary and sufficient conditions for convertibility between pure entangled states under LOSR and highlight some of their consequences, such as the impossibility of catalysis for bipartite pure states. The resource-theoretic perspective also clarifies why it is neither surprising nor problematic that there are mixed entangled states which do not violate any Bell inequality. Our results motivate the study of LOSR-entanglement as a new branch of entanglement theory.

`@article{schmid_understanding_2021, title = {Understanding the interplay of entanglement and nonlocality: motivating and developing a new branch of entanglement theory}, shorttitle = {Understanding the interplay of entanglement and nonlocality}, url = {http://arxiv.org/abs/2004.09194}, abstract = {A standard approach to quantifying resources is to determine which operations on the resources are freely available, and to deduce the partial order over resources that is induced by the relation of convertibility under the free operations. If the resource of interest is the nonclassicality of the correlations embodied in a quantum state, i.e., entanglement, then the common assumption is that the appropriate choice of free operations is Local Operations and Classical Communication (LOCC). We here advocate for the study of a different choice of free operations, namely, Local Operations and Shared Randomness (LOSR), and demonstrate its utility in understanding the interplay between the entanglement of states and the nonlocality of the correlations in Bell experiments. Specifically, we show that the LOSR paradigm (i) provides a resolution of the anomalies of nonlocality, wherein partially entangled states exhibit more nonlocality than maximally entangled states, (ii) entails new notions of genuine multipartite entanglement and nonlocality that are free of the pathological features of the conventional notions, and (iii) makes possible a resource-theoretic account of the self-testing of entangled states which generalizes and simplifies prior results. Along the way, we derive some fundamental results concerning the necessary and sufficient conditions for convertibility between pure entangled states under LOSR and highlight some of their consequences, such as the impossibility of catalysis for bipartite pure states. The resource-theoretic perspective also clarifies why it is neither surprising nor problematic that there are mixed entangled states which do not violate any Bell inequality. Our results motivate the study of LOSR-entanglement as a new branch of entanglement theory.}, urldate = {2021-07-28}, journal = {arXiv:2004.09194 [quant-ph]}, author = {Schmid, David and Fraser, Thomas C. and Kunjwal, Ravi and Sainz, Ana Belen and Wolfe, Elie and Spekkens, Robert W.}, month = may, year = {2021}, note = {arXiv: 2004.09194}, keywords = {Quantum Physics}, }`

- Markus Grassl, Felix Huber, and Andreas Winter. Entropic proofs of Singleton bounds for quantum error-correcting codes.
*arXiv:2010.07902 [quant-ph]*, feb 2021. arXiv: 2010.07902

[BibTeX] [Abstract] [Download PDF]

We show that a relatively simple reasoning using von Neumann entropy inequalities yields a robust proof of the quantum Singleton bound for quantum error-correcting codes (QECC). For entanglement-assisted quantum error-correcting codes (EAQECC) and catalytic codes (CQECC), the generalised quantum Singleton bound was believed to hold for many years until recently one of us found a counterexample [MG, arXiv:2007.01249]. Here, we rectify this state of affairs by proving the correct generalised quantum Singleton bound for CQECC, extending the above-mentioned proof method for QECC; we also prove information-theoretically tight bounds on the entanglement-communication tradeoff for EAQECC. All of the bounds relate block length \$n\$ and code length \$k\$ for given minimum distance \$d\$ and we show that they are robust, in the sense that they hold with small perturbations for codes which only correct most of the erasure errors of less than \$d\$ letters. In contrast to the classical case, the bounds take on qualitatively different forms depending on whether the minimum distance is smaller or larger than half the block length. We also provide a propagation rule, where any pure QECC yields an EAQECC with the same distance and dimension but of shorter block length.

`@article{grassl_entropic_2021_arXiv, title = {Entropic proofs of {Singleton} bounds for quantum error-correcting codes}, url = {http://arxiv.org/abs/2010.07902}, abstract = {We show that a relatively simple reasoning using von Neumann entropy inequalities yields a robust proof of the quantum Singleton bound for quantum error-correcting codes (QECC). For entanglement-assisted quantum error-correcting codes (EAQECC) and catalytic codes (CQECC), the generalised quantum Singleton bound was believed to hold for many years until recently one of us found a counterexample [MG, arXiv:2007.01249]. Here, we rectify this state of affairs by proving the correct generalised quantum Singleton bound for CQECC, extending the above-mentioned proof method for QECC; we also prove information-theoretically tight bounds on the entanglement-communication tradeoff for EAQECC. All of the bounds relate block length \$n\$ and code length \$k\$ for given minimum distance \$d\$ and we show that they are robust, in the sense that they hold with small perturbations for codes which only correct most of the erasure errors of less than \$d\$ letters. In contrast to the classical case, the bounds take on qualitatively different forms depending on whether the minimum distance is smaller or larger than half the block length. We also provide a propagation rule, where any pure QECC yields an EAQECC with the same distance and dimension but of shorter block length.}, urldate = {2021-07-28}, journal = {arXiv:2010.07902 [quant-ph]}, author = {Grassl, Markus and Huber, Felix and Winter, Andreas}, month = feb, year = {2021}, note = {arXiv: 2010.07902}, keywords = {Quantum Physics, Computer Science - Information Theory}, }`

- B. Ahmadi, S. Salimi, and A. S. Khorashad. Refined Definitions of Heat and Work in Quantum Thermodynamics.
*arXiv:1912.01983 [quant-ph]*, jul 2021. arXiv: 1912.01983

[BibTeX] [Abstract] [Download PDF]

In this paper, unambiguous redefinitions of heat and work are presented for quantum thermodynamic systems. We will use genuine reasoning based on which Clausius originally defined work and heat in establishing thermodynamics. The change in the energy which is accompanied by a change in the entropy is identified as heat, while any change in the energy which does not lead to a change in the entropy is known as work. It will be seen that quantum coherence does not allow all the energy exchanged between two quantum systems to be only of the heat form. Several examples will also be discussed. Finally, it will be shown that these refined definitions will strongly affect the entropy production of quantum thermodynamic processes giving new insight into the irreversibility of quantum processes.

`@Article{ahmadi_refined_2021, author = {Ahmadi, B. and Salimi, S. and Khorashad, A. S.}, journal = {arXiv:1912.01983 [quant-ph]}, title = {Refined {Definitions} of {Heat} and {Work} in {Quantum} {Thermodynamics}}, year = {2021}, month = jul, note = {arXiv: 1912.01983}, abstract = {In this paper, unambiguous redefinitions of heat and work are presented for quantum thermodynamic systems. We will use genuine reasoning based on which Clausius originally defined work and heat in establishing thermodynamics. The change in the energy which is accompanied by a change in the entropy is identified as heat, while any change in the energy which does not lead to a change in the entropy is known as work. It will be seen that quantum coherence does not allow all the energy exchanged between two quantum systems to be only of the heat form. Several examples will also be discussed. Finally, it will be shown that these refined definitions will strongly affect the entropy production of quantum thermodynamic processes giving new insight into the irreversibility of quantum processes.}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/1912.01983}, urldate = {2021-07-28}, }`

- Aaron Z. Goldberg, Markus Grassl, Gerd Leuchs, and Luis L. Sánchez-Soto. Quantumness Beyond Entanglement: The Case of Symmetric States.
*arXiv:2110.11361 [quant-ph]*, oct 2021.

[BibTeX] [Abstract] [Download PDF]

It is nowadays accepted that truly quantum correlations can exist even in the absence of entanglement. For the case of symmetric states, a physically trivial unitary transformation can alter a quantum state from entangled to separable and vice versa. We propose to certify the presence of quantumness via an average over all physically relevant modal decompositions. We investigate extremal states for such a measure: SU(2)-coherent states possess the least quantumness whereas the opposite extreme is inhabited by states with maximally spread Majorana constellations.

`@Article{Goldberg2021, author = {Aaron Z. Goldberg and Markus Grassl and Gerd Leuchs and Luis L. Sánchez-Soto}, journal = {arXiv:2110.11361 [quant-ph]}, title = {Quantumness {B}eyond {E}ntanglement: {T}he {C}ase of {S}ymmetric {S}tates}, year = {2021}, month = oct, abstract = {It is nowadays accepted that truly quantum correlations can exist even in the absence of entanglement. For the case of symmetric states, a physically trivial unitary transformation can alter a quantum state from entangled to separable and vice versa. We propose to certify the presence of quantumness via an average over all physically relevant modal decompositions. We investigate extremal states for such a measure: SU(2)-coherent states possess the least quantumness whereas the opposite extreme is inhabited by states with maximally spread Majorana constellations.}, archiveprefix = {arXiv}, eprint = {2110.11361}, keywords = {quant-ph}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211011361G}, }`

- Lucas Chibebe Céleri and Łukasz Rudnicki. Gauge invariant quantum thermodynamics: consequences for the first law.
*arXiv e-prints*, pages arXiv:2104.10153, apr 2021.

[BibTeX] [Abstract] [Download PDF]

Universality of classical thermodynamics rests on the central limit theorem, due to which, measurements of thermal fluctuations are unable to reveal detailed information regarding the microscopic structure of a macroscopic body. When small systems are considered and fluctuations become important, thermodynamic quantities can be understood in the context of classical stochastic mechanics. A fundamental assumption behind thermodynamics is therefore that of coarse-graning, which stems from a substantial lack of control over all degrees of freedom. However, when quantum systems are concerned, one claims a high level of control. As a consequence, information theory plays a major role in the identification of thermodynamic functions. Here, drawing from the concept of gauge symmetry, essential in all modern physical theories, we put forward a new possible, intermediate route. Working within the realm of quantum thermodynamics we explicitly construct physically motivated gauge transformations which encode a gentle variant of coarse- graining behind thermodynamics. As a consequence, we reinterpret quantum work and heat, as well as the role of quantum coherence.

`@Article{ChibebeCeleri2021, author = {Chibebe Céleri, Lucas and Rudnicki, Łukasz}, journal = {arXiv e-prints}, title = {Gauge invariant quantum thermodynamics: consequences for the first law}, year = {2021}, month = apr, pages = {arXiv:2104.10153}, abstract = {Universality of classical thermodynamics rests on the central limit theorem, due to which, measurements of thermal fluctuations are unable to reveal detailed information regarding the microscopic structure of a macroscopic body. When small systems are considered and fluctuations become important, thermodynamic quantities can be understood in the context of classical stochastic mechanics. A fundamental assumption behind thermodynamics is therefore that of coarse-graning, which stems from a substantial lack of control over all degrees of freedom. However, when quantum systems are concerned, one claims a high level of control. As a consequence, information theory plays a major role in the identification of thermodynamic functions. Here, drawing from the concept of gauge symmetry, essential in all modern physical theories, we put forward a new possible, intermediate route. Working within the realm of quantum thermodynamics we explicitly construct physically motivated gauge transformations which encode a gentle variant of coarse- graining behind thermodynamics. As a consequence, we reinterpret quantum work and heat, as well as the role of quantum coherence.}, archiveprefix = {arXiv}, eid = {arXiv:2104.10153}, eprint = {2104.10153}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210410153C}, }`

- Tomasz Linowski and Łukasz Rudnicki. Reduced state of the field and classicality of quantum Gaussian evolution.
*arXiv e-prints*, pages arXiv:2107.03196, jul 2021.

[BibTeX] [Abstract] [Download PDF]

We discuss compatibility between various quantum aspects of bosonic fields, relevant for quantum optics and quantum thermodynamics, and the mesoscopic formalism of reduced state of the field (RSF). In particular, we derive exact conditions under which Gaussian and Bogoliubov-type evolutions can be cast into the RSF framework. In that regard, special emphasis is put on Gaussian thermal operations. To strengthen the link between the RSF formalism and the notion of classicality for bosonic quantum fields, we prove that RSF contains no information about entanglement in two-mode Gaussian states. For the same purpose, we show that the entropic characterisation of RSF by means of the von Neumann entropy is qualitatively the same as its description based on the Wehrl entropy. Our findings help bridge the conceptual gap between quantum and classical mechanics.

`@Article{Linowski2021, author = {Linowski, Tomasz and Rudnicki, Łukasz}, journal = {arXiv e-prints}, title = {Reduced state of the field and classicality of quantum Gaussian evolution}, year = {2021}, month = jul, pages = {arXiv:2107.03196}, abstract = {We discuss compatibility between various quantum aspects of bosonic fields, relevant for quantum optics and quantum thermodynamics, and the mesoscopic formalism of reduced state of the field (RSF). In particular, we derive exact conditions under which Gaussian and Bogoliubov-type evolutions can be cast into the RSF framework. In that regard, special emphasis is put on Gaussian thermal operations. To strengthen the link between the RSF formalism and the notion of classicality for bosonic quantum fields, we prove that RSF contains no information about entanglement in two-mode Gaussian states. For the same purpose, we show that the entropic characterisation of RSF by means of the von Neumann entropy is qualitatively the same as its description based on the Wehrl entropy. Our findings help bridge the conceptual gap between quantum and classical mechanics.}, archiveprefix = {arXiv}, eid = {arXiv:2107.03196}, eprint = {2107.03196}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210703196L}, }`

- Beata Zjawin, David Schmid, Matty J. Hoban, and Ana Belén Sainz. Quantifying EPR: the resource theory of nonclassicality of common-cause assemblages.
*arXiv e-prints*, pages arXiv:2111.10244, nov 2021.

[BibTeX] [Abstract] [Download PDF]

Einstein-Podolsky-Rosen (EPR) steering is often (implicitly or explicitly) taken to be evidence for spooky action-at-a-distance. An alternative perspective on steering – endorsed by EPR themselves – is that Alice has no causal influence on the physical state of Bob’s system; rather, Alice merely updates her knowledge of the state of Bob’s system by performing a measurement on a system correlated with his. In this work, we elaborate on this perspective (from which the very term `steering’ is seen to be inappropriate), and we are led to a resource-theoretic treatment of correlations in EPR scenarios. For both bipartite and multipartite scenarios, we develop the resulting resource theory, wherein the free operations are local operations and shared randomness (LOSR). We show that resource conversion under free operations in this paradigm can be evaluated with a single instance of a semidefinite program, making the problem numerically tractable. Moreover, we find that the structure of the pre-order of resources features interesting properties, such as infinite families of incomparable resources. In showing this, we derive new EPR resource monotones. We also discuss advantages of our approach over a pre-existing proposal for a resource theory of `steering’, and discuss how our approach sheds light on basic questions, such as which multipartite assemblages are classically explainable.

`@Article{Zjawin2021, author = {Zjawin, Beata and Schmid, David and Hoban, Matty J. and Sainz, Ana Belén}, journal = {arXiv e-prints}, title = {Quantifying {EPR}: the resource theory of nonclassicality of common-cause assemblages}, year = {2021}, month = nov, pages = {arXiv:2111.10244}, abstract = {Einstein-Podolsky-Rosen (EPR) steering is often (implicitly or explicitly) taken to be evidence for spooky action-at-a-distance. An alternative perspective on steering - endorsed by EPR themselves - is that Alice has no causal influence on the physical state of Bob's system; rather, Alice merely updates her knowledge of the state of Bob's system by performing a measurement on a system correlated with his. In this work, we elaborate on this perspective (from which the very term `steering' is seen to be inappropriate), and we are led to a resource-theoretic treatment of correlations in EPR scenarios. For both bipartite and multipartite scenarios, we develop the resulting resource theory, wherein the free operations are local operations and shared randomness (LOSR). We show that resource conversion under free operations in this paradigm can be evaluated with a single instance of a semidefinite program, making the problem numerically tractable. Moreover, we find that the structure of the pre-order of resources features interesting properties, such as infinite families of incomparable resources. In showing this, we derive new EPR resource monotones. We also discuss advantages of our approach over a pre-existing proposal for a resource theory of `steering', and discuss how our approach sheds light on basic questions, such as which multipartite assemblages are classically explainable.}, archiveprefix = {arXiv}, eid = {arXiv:2111.10244}, eprint = {2111.10244}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211110244Z}, }`

- Massimiliano Incudini, Fabio Tarocco, Riccardo Mengoni, Alessandra Di Pierro, and Antonio Mandarino. Benchmarking Small-Scale Quantum Devices on Computing Graph Edit Distance.
*arXiv e-prints*, pages arXiv:2111.10183, nov 2021.

[BibTeX] [Abstract] [Download PDF]

Distance measures provide the foundation for many popular algorithms in Machine Learning and Pattern Recognition. Different notions of distance can be used depending on the types of the data the algorithm is working on. For graph-shaped data, an important notion is the Graph Edit Distance (GED) that measures the degree of (dis)similarity between two graphs in terms of the operations needed to make them identical. As the complexity of computing GED is the same as NP-hard problems, it is reasonable to consider approximate solutions. In this paper we present a comparative study of two quantum approaches to computing GED: quantum annealing and variational quantum algorithms, which refer to the two types of quantum hardware currently available, namely quantum annealer and gate-based quantum computer, respectively. Considering the current state of noisy intermediate-scale quantum computers, we base our study on proof-of-principle tests of the performance of these quantum algorithms.

`@Article{Incudini2021a, author = {Incudini, Massimiliano and Tarocco, Fabio and Mengoni, Riccardo and Di Pierro, Alessandra and Mandarino, Antonio}, journal = {arXiv e-prints}, title = {Benchmarking {S}mall-{S}cale {Q}uantum {D}evices on {C}omputing {G}raph {E}dit {D}istance}, year = {2021}, month = nov, pages = {arXiv:2111.10183}, abstract = {Distance measures provide the foundation for many popular algorithms in Machine Learning and Pattern Recognition. Different notions of distance can be used depending on the types of the data the algorithm is working on. For graph-shaped data, an important notion is the Graph Edit Distance (GED) that measures the degree of (dis)similarity between two graphs in terms of the operations needed to make them identical. As the complexity of computing GED is the same as NP-hard problems, it is reasonable to consider approximate solutions. In this paper we present a comparative study of two quantum approaches to computing GED: quantum annealing and variational quantum algorithms, which refer to the two types of quantum hardware currently available, namely quantum annealer and gate-based quantum computer, respectively. Considering the current state of noisy intermediate-scale quantum computers, we base our study on proof-of-principle tests of the performance of these quantum algorithms.}, archiveprefix = {arXiv}, eid = {arXiv:2111.10183}, eprint = {2111.10183}, keywords = {Quantum Physics, Computer Science - Machine Learning}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211110183I}, }`

- Tanmoy Biswas, Oliveira A. de Junior, Michał Horodecki, and Kamil Korzekwa. Fluctuation-dissipation relations for thermodynamic distillation processes.
*arXiv:2105.11759 [quant-ph]*, 5 2021.

[BibTeX] [Abstract] [Download PDF]

The fluctuation-dissipation theorem is a fundamental result in statistical physics that establishes a connection between the response of a system subject to a perturbation and the fluctuations associated with observables in equilibrium. Here we derive its version within a resource-theoretic framework, where one investigates optimal quantum state transitions under thermodynamic constraints. More precisely, we first characterise optimal thermodynamic distillation processes, and then prove a relation between the amount of free energy dissipated in such processes and the free energy fluctuations of the initial state of the system. Our results apply to initial states given by either asymptotically many identical pure systems or arbitrary number of independent energy-incoherent systems, and allow not only for a state transformation, but also for the change of Hamiltonian. The fluctuation-dissipation relations we derive enable us to find the optimal performance of thermodynamic protocols such as work extraction, information erasure and thermodynamically-free communication, up to second-order asymptotics in the number $N$ of processed systems. We thus provide a first rigorous analysis of these thermodynamic protocols for quantum states with coherence between different energy eigenstates in the intermediate regime of large but finite $N$.

`@Article{Biswas2021a, author = {Biswas, Tanmoy and Junior, A. de Oliveira and Horodecki, Michał and Korzekwa, Kamil}, journal = {arXiv:2105.11759 [quant-ph]}, title = {Fluctuation-dissipation relations for thermodynamic distillation processes}, year = {2021}, month = {5}, abstract = {The fluctuation-dissipation theorem is a fundamental result in statistical physics that establishes a connection between the response of a system subject to a perturbation and the fluctuations associated with observables in equilibrium. Here we derive its version within a resource-theoretic framework, where one investigates optimal quantum state transitions under thermodynamic constraints. More precisely, we first characterise optimal thermodynamic distillation processes, and then prove a relation between the amount of free energy dissipated in such processes and the free energy fluctuations of the initial state of the system. Our results apply to initial states given by either asymptotically many identical pure systems or arbitrary number of independent energy-incoherent systems, and allow not only for a state transformation, but also for the change of Hamiltonian. The fluctuation-dissipation relations we derive enable us to find the optimal performance of thermodynamic protocols such as work extraction, information erasure and thermodynamically-free communication, up to second-order asymptotics in the number $N$ of processed systems. We thus provide a first rigorous analysis of these thermodynamic protocols for quantum states with coherence between different energy eigenstates in the intermediate regime of large but finite $N$.}, archiveprefix = {arXiv}, eprint = {2105.11759}, groups = {Michal_H}, keywords = {Quantum Physics, Condensed Matter - Statistical Mechanics}, primaryclass = {quant-ph}, url = {https://arxiv.org/pdf/2105.11759}, }`

- Rivu Gupta, Saptarshi Roy, Tamoghna Das, and Aditi Sen De. Quantum illumination with a light absorbing target.
*arXiv e-prints*, pages arXiv:2111.01069, nov 2021. acknowledgement for ICTQT IRAP included

[BibTeX] [Abstract] [Download PDF]

In a quantum illumination (QI) protocol, the task is to detect the presence of the target which is typically modelled by a partially reflecting beam splitter. We analyze the performance of QI when the target absorbs part of the light that falls on it, thereby making the scenario more realistic. We present an optical setup that models a target with these characteristics and explore its detectability in the quantum domain in terms of the Chernoff bound (CB). For an idler-free setup, we use the coherent state for QI while the two mode squeezed vacuum (TMSV) state is employed in the signal-idler scheme. In both the cases, we report an absorption-induced enhancement of the detection efficiency indicated by a lowering of CB with increasing amounts of absorption. Interestingly, we show that in the presence of absorption, a more intense thermal background can lead to target detection with enhanced efficiency. Moreover, we observe that the quantum advantage persists even for finite amounts of absorption. However, we find that the quantum advantage offered by TMSV decreases monotonically with absorption, and becomes vanishingly small in the high absorption regime. We also demonstrate the optimality of both the coherent and the TMSV states in their respective setups (idler-free and signal-idler) in the limit of low reflectivity and absorption.

`@Article{Gupta2021, author = {Gupta, Rivu and Roy, Saptarshi and Das, Tamoghna and De, Aditi Sen}, journal = {arXiv e-prints}, title = {Quantum illumination with a light absorbing target}, year = {2021}, month = nov, pages = {arXiv:2111.01069}, abstract = {In a quantum illumination (QI) protocol, the task is to detect the presence of the target which is typically modelled by a partially reflecting beam splitter. We analyze the performance of QI when the target absorbs part of the light that falls on it, thereby making the scenario more realistic. We present an optical setup that models a target with these characteristics and explore its detectability in the quantum domain in terms of the Chernoff bound (CB). For an idler-free setup, we use the coherent state for QI while the two mode squeezed vacuum (TMSV) state is employed in the signal-idler scheme. In both the cases, we report an absorption-induced enhancement of the detection efficiency indicated by a lowering of CB with increasing amounts of absorption. Interestingly, we show that in the presence of absorption, a more intense thermal background can lead to target detection with enhanced efficiency. Moreover, we observe that the quantum advantage persists even for finite amounts of absorption. However, we find that the quantum advantage offered by TMSV decreases monotonically with absorption, and becomes vanishingly small in the high absorption regime. We also demonstrate the optimality of both the coherent and the TMSV states in their respective setups (idler-free and signal-idler) in the limit of low reflectivity and absorption.}, archiveprefix = {arXiv}, eid = {arXiv:2111.01069}, eprint = {2111.01069}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, note = {acknowledgement for ICTQT IRAP included}, url = {https://doi.org/10.48550/arXiv.2111.01069}, }`

- Anubhav Chaturvedi, Marcin Pawłowski, and Debashis Saha. Quantum description of reality is empirically incomplete.
*arXiv e-prints*, pages arXiv:2110.13124, oct 2021.

[BibTeX] [Abstract] [Download PDF]

Empirical falsifiability of the predictions of physical theories is the cornerstone of the scientific method. Physical theories attribute empirically falsifiable operational properties to sets of physical preparations. A theory is said to be empirically complete if such properties allow for a not fine-tuned realist explanation, as properties of underlying probability distributions over states of reality. Such theories satisfy a family of equalities among fundamental operational properties, characterized exclusively by the number of preparations. Quantum preparations deviate from these equalities, and the maximal quantum deviation increases with the number of preparations. These deviations not only signify the incompleteness of the operational quantum formalism, but they simultaneously imply quantum over classical advantage in suitably constrained one-way communication tasks, highlighting the delicate interplay between the two.

`@Article{Chaturvedi2021_arXiv, author = {Chaturvedi, Anubhav and Paw{\l}owski, Marcin and Saha, Debashis}, journal = {arXiv e-prints}, title = {Quantum description of reality is empirically incomplete}, year = {2021}, month = oct, pages = {arXiv:2110.13124}, abstract = {Empirical falsifiability of the predictions of physical theories is the cornerstone of the scientific method. Physical theories attribute empirically falsifiable operational properties to sets of physical preparations. A theory is said to be empirically complete if such properties allow for a not fine-tuned realist explanation, as properties of underlying probability distributions over states of reality. Such theories satisfy a family of equalities among fundamental operational properties, characterized exclusively by the number of preparations. Quantum preparations deviate from these equalities, and the maximal quantum deviation increases with the number of preparations. These deviations not only signify the incompleteness of the operational quantum formalism, but they simultaneously imply quantum over classical advantage in suitably constrained one-way communication tasks, highlighting the delicate interplay between the two.}, archiveprefix = {arXiv}, eid = {arXiv:2110.13124}, eprint = {2110.13124}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211013124C}, }`

- Nikolai Miklin, Mariami Gachechiladze, George Moreno, and Rafael Chaves. Causal inference with imperfect instrumental variables.
*arXiv e-prints*, pages arXiv:2111.03029, nov 2021.

[BibTeX] [Abstract] [Download PDF]

Instrumental variables allow for quantification of cause and effect relationships even in the absence of interventions. To achieve this, a number of causal assumptions must be met, the most important of which is the independence assumption, which states that the instrument and any confounding factor must be independent. However, if this independence condition is not met, can we still work with imperfect instrumental variables? Imperfect instruments can manifest themselves by violations of the instrumental inequalities that constrain the set of correlations in the scenario. In this paper, we establish a quantitative relationship between such violations of instrumental inequalities and the minimal amount of measurement dependence required to explain them. As a result, we provide adapted inequalities that are valid in the presence of a relaxed measurement dependence assumption in the instrumental scenario. This allows for the adaptation of existing and new lower bounds on the average causal effect for instrumental scenarios with binary outcomes. Finally, we discuss our findings in the context of quantum mechanics.

`@Article{Miklin2021, author = {Miklin, Nikolai and Gachechiladze, Mariami and Moreno, George and Chaves, Rafael}, journal = {arXiv e-prints}, title = {Causal inference with imperfect instrumental variables}, year = {2021}, month = nov, pages = {arXiv:2111.03029}, abstract = {Instrumental variables allow for quantification of cause and effect relationships even in the absence of interventions. To achieve this, a number of causal assumptions must be met, the most important of which is the independence assumption, which states that the instrument and any confounding factor must be independent. However, if this independence condition is not met, can we still work with imperfect instrumental variables? Imperfect instruments can manifest themselves by violations of the instrumental inequalities that constrain the set of correlations in the scenario. In this paper, we establish a quantitative relationship between such violations of instrumental inequalities and the minimal amount of measurement dependence required to explain them. As a result, we provide adapted inequalities that are valid in the presence of a relaxed measurement dependence assumption in the instrumental scenario. This allows for the adaptation of existing and new lower bounds on the average causal effect for instrumental scenarios with binary outcomes. Finally, we discuss our findings in the context of quantum mechanics.}, archiveprefix = {arXiv}, eid = {arXiv:2111.03029}, eprint = {2111.03029}, keywords = {Statistics - Machine Learning, Computer Science - Machine Learning, Quantum Physics}, primaryclass = {stat.ML}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211103029M}, }`

- Iris Agresti, Davide Poderini, Beatrice Polacchi, Nikolai Miklin, Mariami Gachechiladze, Alessia Suprano, Emanuele Polino, Giorgio Milani, Gonzalo Carvacho, Rafael Chaves, and Fabio Sciarrino. Experimental test of quantum causal influences.
*arXiv e-prints*, pages arXiv:2108.08926, aug 2021.

[BibTeX] [Abstract] [Download PDF]

Since Bell’s theorem, it is known that the concept of local realism fails to explain quantum phenomena. Indeed, the violation of a Bell inequality has become a synonym of the incompatibility of quantum theory with our classical notion of cause and effect. As recently discovered, however, the instrumental scenario — a tool of central importance in causal inference — allows for signatures of nonclassicality that do not hinge on this paradigm. If, instead of relying on observational data only, we can also intervene in our experimental setup, quantum correlations can violate classical bounds on the causal influence even in scenarios where no violation of a Bell inequality is ever possible. That is, through interventions, we can witness the quantum behaviour of a system that would look classical otherwise. Using a photonic setup — faithfully implementing the instrumental causal structure and allowing to switch between the observational and interventional modes in a run to run basis — we experimentally observe this new witness of nonclassicality for the first time. In parallel, we also test quantum bounds for the causal influence, showing that they provide a reliable tool for quantum causal modelling.

`@Article{Agresti2021, author = {Agresti, Iris and Poderini, Davide and Polacchi, Beatrice and Miklin, Nikolai and Gachechiladze, Mariami and Suprano, Alessia and Polino, Emanuele and Milani, Giorgio and Carvacho, Gonzalo and Chaves, Rafael and Sciarrino, Fabio}, journal = {arXiv e-prints}, title = {Experimental test of quantum causal influences}, year = {2021}, month = aug, pages = {arXiv:2108.08926}, abstract = {Since Bell's theorem, it is known that the concept of local realism fails to explain quantum phenomena. Indeed, the violation of a Bell inequality has become a synonym of the incompatibility of quantum theory with our classical notion of cause and effect. As recently discovered, however, the instrumental scenario -- a tool of central importance in causal inference -- allows for signatures of nonclassicality that do not hinge on this paradigm. If, instead of relying on observational data only, we can also intervene in our experimental setup, quantum correlations can violate classical bounds on the causal influence even in scenarios where no violation of a Bell inequality is ever possible. That is, through interventions, we can witness the quantum behaviour of a system that would look classical otherwise. Using a photonic setup -- faithfully implementing the instrumental causal structure and allowing to switch between the observational and interventional modes in a run to run basis -- we experimentally observe this new witness of nonclassicality for the first time. In parallel, we also test quantum bounds for the causal influence, showing that they provide a reliable tool for quantum causal modelling.}, archiveprefix = {arXiv}, eid = {arXiv:2108.08926}, eprint = {2108.08926}, keywords = {Quantum Physics, Physics - Optics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210808926A}, }`

- Ray Ganardi, Marek Miller, Tomasz Paterek, and Marek Żukowski. Hierarchy of correlation quantifiers comparable to negativity.
*arXiv e-prints*, pages arXiv:2111.11887, nov 2021.

[BibTeX] [Abstract] [Download PDF]

Quantum systems generally exhibit different kinds of correlations. In order to compare them on equal footing, one uses the so-called distance-based approach where different types of correlations are captured by the distance to different set of states. However, these quantifiers are usually hard to compute as their definition involves optimization aiming to find the closest states within the set. On the other hand, negativity is one of the few computable entanglement monotones, but its comparison with other correlations required further justification. Here we place negativity as part of a family of correlation measures that has a distance-based construction. We introduce a suitable distance, discuss the emerging measures and their applications, and compare them to relative entropy-based correlation quantifiers. This work is a step towards correlation measures that are simultaneously comparable and computable.

`@Article{Ganardi2021, author = {Ganardi, Ray and Miller, Marek and Paterek, Tomasz and {\.Z}ukowski, Marek}, journal = {arXiv e-prints}, title = {Hierarchy of correlation quantifiers comparable to negativity}, year = {2021}, month = nov, pages = {arXiv:2111.11887}, abstract = {Quantum systems generally exhibit different kinds of correlations. In order to compare them on equal footing, one uses the so-called distance-based approach where different types of correlations are captured by the distance to different set of states. However, these quantifiers are usually hard to compute as their definition involves optimization aiming to find the closest states within the set. On the other hand, negativity is one of the few computable entanglement monotones, but its comparison with other correlations required further justification. Here we place negativity as part of a family of correlation measures that has a distance-based construction. We introduce a suitable distance, discuss the emerging measures and their applications, and compare them to relative entropy-based correlation quantifiers. This work is a step towards correlation measures that are simultaneously comparable and computable.}, archiveprefix = {arXiv}, eid = {arXiv:2111.11887}, eprint = {2111.11887}, keywords = {Quantum Physics}, primaryclass = {quant-ph}, url = {https://ui.adsabs.harvard.edu/abs/2021arXiv211111887G}, }`

- Karol Horodecki, Marek Winczewski, and Siddhartha Das. Fundamental limitations on device-independent quantum conference key agreement.
*arXiv e-prints*, pages arXiv:2111.02467, nov 2021.

[BibTeX] [Abstract] [Download PDF]

We provide several general upper bounds on device-independent conference key agreement (DI-CKA) against the quantum adversary. They include bounds by reduced entanglement measures and those based on multipartite secrecy monotones such as reduced cc-squashed entanglement. We compare the latter bound with the known lower bound for the protocol of conference key distillation based on the parity-CHSH game. We also show that the gap between DI-CKA rate and the rate of device-dependent is inherited from the bipartite gap between device-independent and device-dependent key rates, giving examples that exhibit the strict gap.

`@Article{arXiv_Horodecki2021, author = {Horodecki, Karol and Winczewski, Marek and Das, Siddhartha}, journal = {arXiv e-prints}, title = {Fundamental limitations on device-independent quantum conference key agreement}, year = {2021}, month = nov, pages = {arXiv:2111.02467}, abstract = {We provide several general upper bounds on device-independent conference key agreement (DI-CKA) against the quantum adversary. They include bounds by reduced entanglement measures and those based on multipartite secrecy monotones such as reduced cc-squashed entanglement. We compare the latter bound with the known lower bound for the protocol of conference key distillation based on the parity-CHSH game. We also show that the gap between DI-CKA rate and the rate of device-dependent is inherited from the bipartite gap between device-independent and device-dependent key rates, giving examples that exhibit the strict gap.}, archiveprefix = {arXiv}, eid = {arXiv:2111.02467}, eprint = {2111.02467}, keywords = {Quantum Physics, Computer Science - Information Theory, Mathematical Physics}, primaryclass = {quant-ph}, url = {https://arxiv.org/pdf/2111.02467}, }`

- Ravishankar Ramanathan, Michał Banacki, and Paweł Horodecki. No-signaling-proof randomness extraction from public weak sources.
*arXiv:2108.08819 [quant-ph]*, aug 2021. acknowledgement for ICTQT IRAP included

[BibTeX] [Abstract] [Download PDF]

The extraction of randomness from weakly random seeds is a topic of central importance in cryptography. Weak sources of randomness can be considered to be either private or public, where public sources such as the NIST randomness beacon broadcast the random bits once they are generated. The problem of device-independent randomness extraction from weak public sources against no-signalling adversaries has remained open. In this paper, we show protocols for device-independent and one-sided device-independent amplification of randomness from weak public Santha Vazirani (SV) sources that use a finite number of devices and are secure against no-signaling adversaries. Specifically, under the assumption that the device behavior is as prescribed by quantum mechanics the protocols allow for amplification of public $\epsilon$-SV sources for arbitrary initial $\epsilon\in łeft[0,0.5\right)$. On the other hand, when only the assumption of no-signaling between the components of the device is made, the protocols allow for amplification of a limited set of weak public SV sources.

`@Article{arxiv_ramanathan_no-signaling-proof_2021, author = {Ramanathan, Ravishankar and Banacki, Michał and Horodecki, Paweł}, journal = {arXiv:2108.08819 [quant-ph]}, title = {No-signaling-proof randomness extraction from public weak sources}, note = {acknowledgement for ICTQT IRAP included}, year = {2021}, month = aug, note = {arXiv: 2108.08819}, abstract = {The extraction of randomness from weakly random seeds is a topic of central importance in cryptography. Weak sources of randomness can be considered to be either private or public, where public sources such as the NIST randomness beacon broadcast the random bits once they are generated. The problem of device-independent randomness extraction from weak public sources against no-signalling adversaries has remained open. In this paper, we show protocols for device-independent and one-sided device-independent amplification of randomness from weak public Santha Vazirani (SV) sources that use a finite number of devices and are secure against no-signaling adversaries. Specifically, under the assumption that the device behavior is as prescribed by quantum mechanics the protocols allow for amplification of public $\epsilon$-SV sources for arbitrary initial $\epsilon\in \left[0,0.5\right)$. On the other hand, when only the assumption of no-signaling between the components of the device is made, the protocols allow for amplification of a limited set of weak public SV sources.}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {https://arxiv.org/abs/2108.08819}, }`

- Marek Winczewski, Antonio Mandarino, Michał Horodecki, and Robert Alicki. Bypassing the Intermediate Times Dilemma for Open Quantum System. , 2021. doi:10.48550/ARXIV.2106.05776

[BibTeX] [Download PDF]`@article{arXiv_Bypasing_Dillema, doi = {10.48550/ARXIV.2106.05776}, url = {https://arxiv.org/abs/2106.05776}, author = {Winczewski, Marek and Mandarino, Antonio and Horodecki, Michał and Alicki, Robert}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Bypassing the Intermediate Times Dilemma for Open Quantum System}, publisher = {arXiv}, year = {2021}, copyright = {Creative Commons Attribution 4.0 International} }`

- Marek Winczewski and Robert Alicki. Renormalization in the Theory of Open Quantum Systems via the Self-Consistency Condition. , 2021. doi:10.48550/ARXIV.2112.11962

[BibTeX] [Download PDF]`@article{arXiv_Renormalization_OQS, doi = {10.48550/ARXIV.2112.11962}, url = {https://arxiv.org/abs/2112.11962}, author = {Winczewski, Marek and Alicki, Robert}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Renormalization in the Theory of Open Quantum Systems via the Self-Consistency Condition}, publisher = {arXiv}, year = {2021}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, and Marek Żukowski. Optimal interferometry for Bell$-$nonclassicality by a vacuum$-$one$-$photon qubit. , 2021. doi:10.48550/ARXIV.2109.10170

[BibTeX] [Download PDF]`@article{https://doi.org/10.48550/arxiv.2109.10170, doi = {10.48550/ARXIV.2109.10170}, url = {https://arxiv.org/abs/2109.10170}, author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Żukowski, Marek}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Optimal interferometry for {Bell}$-$nonclassicality by a vacuum$-$one$-$photon qubit}, publisher = {arXiv}, year = {2021}, copyright = {arXiv.org perpetual, non-exclusive license} }`

- M. Rosicka, S. Szarek, A. Rutkowski, P. Gnaciński, and M. Horodecki. Constructive nonlocal games with very small classical values. 2021. doi:10.48550/ARXIV.2112.07741

[BibTeX] [Download PDF]`@misc{arxiv-Rosicka-Szarek, doi = {10.48550/ARXIV.2112.07741}, url = {https://arxiv.org/abs/2112.07741}, author = {Rosicka, M. and Szarek, S. and Rutkowski, A. and Gnaciński, P. and Horodecki, M.}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Constructive nonlocal games with very small classical values}, publisher = {arXiv}, year = {2021}, copyright = {arXiv.org perpetual, non-exclusive license} }`

### 2020

- Victoria J. Wright and Stefan Weigert. General Probabilistic Theories with a Gleason-type Theorem.
*arXiv:2005.14166 [quant-ph]*, 2020. arXiv:2005.14166 [quant-ph]

[BibTeX]`@article{wright2020general, title={General Probabilistic Theories with a Gleason-type Theorem}, author={Wright, Victoria J and Weigert, Stefan}, journal={arXiv:2005.14166 [quant-ph]}, year={2020}, note={arXiv:2005.14166 [quant-ph]} }`

- Anubhav Chaturvedi, Máté. Farkas, and Victoria J. Wright. Characterising and bounding the set of quantum behaviours in contextuality scenarios.
*arXiv:2010.05853 [quant-ph]*, 2020. arXiv:2010.05853 [quant-ph]

[BibTeX]`@article{chaturvedi2020characterising, title={Characterising and bounding the set of quantum behaviours in contextuality scenarios}, author={Chaturvedi, Anubhav and Farkas, M{\'a}t{\'e} and Wright, Victoria J}, journal={arXiv:2010.05853 [quant-ph]}, year={2020}, note={arXiv:2010.05853 [quant-ph]} }`

- Markus Grassl. Entanglement-Assisted Quantum Communication Beating the Quantum Singleton Bound.
*arXiv:2007.01249 [quant-ph]*, jul 2020. arXiv:2007.01249 [quant-ph]

[BibTeX] [Download PDF]`@article{Grassl_2020_Entanglement_arXiv, title = {Entanglement-Assisted Quantum Communication Beating the Quantum {S}ingleton Bound}, url = {https://arxiv.org/abs/2007.01249}, urldate = {2020-08-02}, abstract = {}, journal = {arXiv:2007.01249 [quant-ph]}, author = {Grassl, Markus}, month = jul, year = {2020}, note = {arXiv:2007.01249 [quant-ph]}, keywords = {} }`

- Aaron Z. Goldberg, Andrei B. Klimov, Markus Grassl, Gerd Leuchs, and Luis L. Sánchez-Soto. Extremal quantum states.
*arXiv:2010.04732 [quant-ph]*, oct 2020. arXiv:2010.04732 [quant-ph]

[BibTeX] [Download PDF]`@article{Golberg_2020_ExtremalQuantumStates_arXiv, title = {Extremal quantum states}, url = {https://arxiv.org/abs/}, urldate = {2020-10-09}, abstract = {}, journal = {arXiv:2010.04732 [quant-ph]}, author = {Goldberg, Aaron Z. and Klimov, Andrei B. and Grassl, Markus and Leuchs, Gerd and S{\'a}nchez-Soto, Luis L.}, month = oct, year = {2020}, note = {arXiv:2010.04732 [quant-ph]}, keywords = {} }`

- Markus Grassl. Algebraic Quantum Codes: Linking Quantum Mechanics and Discrete Mathematics.
*arXiv:2011.06996 [cs.IT-ph]*, nov 2020. arXiv:2011.06996 [cs.IT]

[BibTeX] [Download PDF]`@article{Grassl_2020_Quantum_Codes_arXiv, title = {Algebraic Quantum Codes: Linking Quantum Mechanics and Discrete Mathematics}, url = {https://arxiv.org/abs/2011.06996}, urldate = {2020-11-13}, abstract = {}, journal = {arXiv:2011.06996 [cs.IT-ph]}, author = {Grassl, Markus}, month = nov, year = {2020}, note = {arXiv:2011.06996 [cs.IT]}, keywords = {} }`

- David Schmid, John H. Selby, Matthew F. Pusey, and Robert W. Spekkens. A structure theorem for generalized-noncontextual ontological models.
*arXiv:2005.07161 [quant-ph]*, may 2020. arXiv: 2005.07161

[BibTeX] [Abstract] [Download PDF]

It is useful to have a criterion for when the predictions of an operational theory should be considered classically explainable. Here we take the criterion to be that the theory admits of a generalized-noncontextual ontological model. Existing works on generalized noncontextuality have focused on experimental scenarios having a simple structure, typically, prepare-measure scenarios. Here, we formally extend the framework of ontological models as well as the principle of generalized noncontextuality to arbitrary compositional scenarios. We leverage this process-theoretic framework to prove that, under some reasonable assumptions, every generalized-noncontextual ontological model of a tomographically local operational theory has a surprisingly rigid and simple mathematical structure; in short, it corresponds to a frame representation which is not overcomplete. One consequence of this theorem is that the largest number of ontic states possible in any such model is given by the dimension of the associated generalized probabilistic theory. This constraint is useful for generating noncontextuality no-go theorems as well as techniques for experimentally certifying contextuality. Along the way, we extend known results concerning the equivalence of different notions of classicality from prepare-measure scenarios to arbitrary compositional scenarios. Specifically, we prove a correspondence between the following three notions of classical explainability of an operational theory: (i) admitting a noncontextual ontological model, (ii) admitting of a positive quasiprobability representation, and (iii) being simplex-embeddable.

`@article{schmid_structure_2020, title = {A structure theorem for generalized-noncontextual ontological models}, url = {http://arxiv.org/abs/2005.07161}, abstract = {It is useful to have a criterion for when the predictions of an operational theory should be considered classically explainable. Here we take the criterion to be that the theory admits of a generalized-noncontextual ontological model. Existing works on generalized noncontextuality have focused on experimental scenarios having a simple structure, typically, prepare-measure scenarios. Here, we formally extend the framework of ontological models as well as the principle of generalized noncontextuality to arbitrary compositional scenarios. We leverage this process-theoretic framework to prove that, under some reasonable assumptions, every generalized-noncontextual ontological model of a tomographically local operational theory has a surprisingly rigid and simple mathematical structure; in short, it corresponds to a frame representation which is not overcomplete. One consequence of this theorem is that the largest number of ontic states possible in any such model is given by the dimension of the associated generalized probabilistic theory. This constraint is useful for generating noncontextuality no-go theorems as well as techniques for experimentally certifying contextuality. Along the way, we extend known results concerning the equivalence of different notions of classicality from prepare-measure scenarios to arbitrary compositional scenarios. Specifically, we prove a correspondence between the following three notions of classical explainability of an operational theory: (i) admitting a noncontextual ontological model, (ii) admitting of a positive quasiprobability representation, and (iii) being simplex-embeddable.}, urldate = {2020-09-04}, journal = {arXiv:2005.07161 [quant-ph]}, author = {Schmid, David and Selby, John H. and Pusey, Matthew F. and Spekkens, Robert W.}, month = may, year = {2020}, note = {arXiv: 2005.07161}, keywords = {Quantum Physics}, }`

- Mariami Gachechiladze, Nikolai Miklin, and Rafael Chaves. Quantifying causal influences in the presence of a quantum common cause.
*arXiv:2007.01221 [quant-ph, stat]*, jul 2020. arXiv: 2007.01221

[BibTeX] [Abstract] [Download PDF]

Quantum mechanics challenges our intuition on the cause-effect relations in nature. Some fundamental concepts, including Reichenbach’s common cause principle or the notion of local realism, have to be reconsidered. Traditionally, this is witnessed by the violation of a Bell inequality. But are Bell inequalities the only signature of the incompatibility between quantum correlations and causality theory? Motivated by this question we introduce a general framework able to estimate causal influences between two variables, without the need of interventions and irrespectively of the classical, quantum, or even post-quantum nature of a common cause. In particular, by considering the simplest instrumental scenario — for which violation of Bell inequalities is not possible — we show that every pure bipartite entangled state violates the classical bounds on causal influence, thus answering in negative to the posed question and opening a new venue to explore the role of causality within quantum theory.

`@article{gachechiladze_quantifying_2020, title = {Quantifying causal influences in the presence of a quantum common cause}, url = {http://arxiv.org/abs/2007.01221}, abstract = {Quantum mechanics challenges our intuition on the cause-effect relations in nature. Some fundamental concepts, including Reichenbach's common cause principle or the notion of local realism, have to be reconsidered. Traditionally, this is witnessed by the violation of a Bell inequality. But are Bell inequalities the only signature of the incompatibility between quantum correlations and causality theory? Motivated by this question we introduce a general framework able to estimate causal influences between two variables, without the need of interventions and irrespectively of the classical, quantum, or even post-quantum nature of a common cause. In particular, by considering the simplest instrumental scenario -- for which violation of Bell inequalities is not possible -- we show that every pure bipartite entangled state violates the classical bounds on causal influence, thus answering in negative to the posed question and opening a new venue to explore the role of causality within quantum theory.}, urldate = {2020-09-04}, journal = {arXiv:2007.01221 [quant-ph, stat]}, author = {Gachechiladze, Mariami and Miklin, Nikolai and Chaves, Rafael}, month = jul, year = {2020}, note = {arXiv: 2007.01221}, keywords = {Quantum Physics, Statistics - Machine Learning}, }`

- Lukas Knips, Jan Dziewior, Waldemar Kłobus, Wiesław Laskowski, Tomasz Paterek, Peter J. Shadbolt, Harald Weinfurter, and Jasmin D. A. Meinecke. Multipartite entanglement analysis from random correlations.
*npj Quantum Information*, 6(1):51, dec 2020. doi:10.1038/s41534-020-0281-5

[BibTeX] [Abstract] [Download PDF]

Abstract Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.

`@Article{knips_multipartite_2020_arXiv, author = {Knips, Lukas and Dziewior, Jan and Kłobus, Waldemar and Laskowski, Wiesław and Paterek, Tomasz and Shadbolt, Peter J. and Weinfurter, Harald and Meinecke, Jasmin D. A.}, journal = {npj Quantum Information}, title = {Multipartite entanglement analysis from random correlations}, year = {2020}, issn = {2056-6387}, month = dec, number = {1}, pages = {51}, volume = {6}, abstract = {Abstract Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.}, doi = {10.1038/s41534-020-0281-5}, language = {en}, url = {http://www.nature.com/articles/s41534-020-0281-5}, urldate = {2021-05-10}, }`

- Ravishankar Ramanathan, Michał Horodecki, Hammad Anwer, Stefano Pironio, Karol Horodecki, Marcus Grünfeld, Sadiq Muhammad, Mohamed Bourennane, and Paweł Horodecki. Practical No-Signalling proof Randomness Amplification using Hardy paradoxes and its experimental implementation.
*arXiv:1810.11648 [quant-ph]*, sep 2020. arXiv: 1810.11648

[BibTeX] [Abstract] [Download PDF]

Device-Independent (DI) security is the best form of quantum cryptography, providing information-theoretic security based on the very laws of nature. In its highest form, security is guaranteed against adversaries limited only by the no-superluminal signalling rule of relativity. The task of randomness amplification, to generate secure fully uniform bits starting from weakly random seeds, is of both cryptographic and foundational interest, being important for the generation of cryptographically secure random numbers as well as bringing deep connections to the existence of free-will. DI no-signalling proof protocols for this fundamental task have thus far relied on esoteric proofs of non-locality termed pseudo-telepathy games, complicated multi-party setups or high-dimensional quantum systems, and have remained out of reach of experimental implementation. In this paper, we construct the first practically relevant no-signalling proof DI protocols for randomness amplification based on the simplest proofs of Bell non-locality and illustrate them with an experimental implementation in a quantum optical setup using polarised photons. Technically, we relate the problem to the vast field of Hardy paradoxes, without which it would be impossible to achieve amplification of arbitrarily weak sources in the simplest Bell non-locality scenario consisting of two parties choosing between two binary inputs. Furthermore, we identify a deep connection between proofs of the celebrated Kochen-Specker theorem and Hardy paradoxes that enables us to construct Hardy paradoxes with the non-zero probability taking any value in \$(0,1]\$. Our methods enable us, under the fair-sampling assumption of the experiment, to realize up to \$25\$ bits of randomness in \$20\$ hours of experimental data collection from an initial private source of randomness \$0.1\$ away from uniform.

`@Article{ramanathan_practical_2020, author = {Ramanathan, Ravishankar and Horodecki, Michał and Anwer, Hammad and Pironio, Stefano and Horodecki, Karol and Grünfeld, Marcus and Muhammad, Sadiq and Bourennane, Mohamed and Horodecki, Paweł}, journal = {arXiv:1810.11648 [quant-ph]}, title = {Practical {No}-{Signalling} proof {Randomness} {Amplification} using {Hardy} paradoxes and its experimental implementation}, year = {2020}, month = sep, note = {arXiv: 1810.11648}, abstract = {Device-Independent (DI) security is the best form of quantum cryptography, providing information-theoretic security based on the very laws of nature. In its highest form, security is guaranteed against adversaries limited only by the no-superluminal signalling rule of relativity. The task of randomness amplification, to generate secure fully uniform bits starting from weakly random seeds, is of both cryptographic and foundational interest, being important for the generation of cryptographically secure random numbers as well as bringing deep connections to the existence of free-will. DI no-signalling proof protocols for this fundamental task have thus far relied on esoteric proofs of non-locality termed pseudo-telepathy games, complicated multi-party setups or high-dimensional quantum systems, and have remained out of reach of experimental implementation. In this paper, we construct the first practically relevant no-signalling proof DI protocols for randomness amplification based on the simplest proofs of Bell non-locality and illustrate them with an experimental implementation in a quantum optical setup using polarised photons. Technically, we relate the problem to the vast field of Hardy paradoxes, without which it would be impossible to achieve amplification of arbitrarily weak sources in the simplest Bell non-locality scenario consisting of two parties choosing between two binary inputs. Furthermore, we identify a deep connection between proofs of the celebrated Kochen-Specker theorem and Hardy paradoxes that enables us to construct Hardy paradoxes with the non-zero probability taking any value in \$(0,1]\$. Our methods enable us, under the fair-sampling assumption of the experiment, to realize up to \$25\$ bits of randomness in \$20\$ hours of experimental data collection from an initial private source of randomness \$0.1\$ away from uniform.}, groups = {Michal_H, Pawel_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/1810.11648}, urldate = {2021-05-11}, }`

- Michał Banacki, Marcin Marciniak, Karol Horodecki, and Paweł Horodecki. Information backflow may not indicate quantum memory.
*arXiv:2008.12638 [quant-ph]*, aug 2020. arXiv: 2008.12638

[BibTeX] [Abstract] [Download PDF]

We analyze recent approaches to quantum Markovianity and how they relate to the proper definition of quantum memory. We point out that the well-known criterion of information backflow may not correctly report character of the memory falsely signaling its quantumness. Therefore, as a complement to the well-known criteria, we propose several concepts of elementary dynamical maps. Maps of this type do not increase distinguishability of states which are indistinguishable by von Neumann measurements in a given basis. Those notions and convexity allows us to define general classes of processes without quantum memory in a weak and strong sense. Finally, we provide a practical characterization of the most intuitive class in terms of the new concept of witness of quantum information backflow.

`@Article{banacki_information_2020, author = {Banacki, Michał and Marciniak, Marcin and Horodecki, Karol and Horodecki, Paweł}, journal = {arXiv:2008.12638 [quant-ph]}, title = {Information backflow may not indicate quantum memory}, year = {2020}, month = aug, note = {arXiv: 2008.12638}, abstract = {We analyze recent approaches to quantum Markovianity and how they relate to the proper definition of quantum memory. We point out that the well-known criterion of information backflow may not correctly report character of the memory falsely signaling its quantumness. Therefore, as a complement to the well-known criteria, we propose several concepts of elementary dynamical maps. Maps of this type do not increase distinguishability of states which are indistinguishable by von Neumann measurements in a given basis. Those notions and convexity allows us to define general classes of processes without quantum memory in a weak and strong sense. Finally, we provide a practical characterization of the most intuitive class in terms of the new concept of witness of quantum information backflow.}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2008.12638}, urldate = {2021-07-28}, }`

- Ravishankar Ramanathan, Michał Banacki, Ricard Ravell Rodríguez, and Paweł Horodecki. Single trusted qubit is necessary and sufficient for quantum realisation of extremal no-signaling correlations.
*arXiv:2004.14782 [quant-ph]*, apr 2020. arXiv: 2004.14782

[BibTeX] [Abstract] [Download PDF]

Quantum statistics can be considered from the perspective of postquantum no-signaling theories in which either none or only a certain number of quantum systems are trusted. In these scenarios, the role of states is played by the so-called no-signaling boxes or no-signaling assemblages respectively. It has been shown so far that in the usual Bell non-locality scenario with a single measurement run, quantum statistics can never reproduce an extremal non-local point within the set of no-signaling boxes. We provide here a general no-go rule showing that the latter stays true even if arbitrary sequential measurements are allowed. On the other hand, we prove a positive result showing that already a single trusted qubit is enough for quantum theory to produce a self-testable extremal point within the corresponding set of no-signaling assemblages. This result opens up the possibility for security proofs of cryptographic protocols against general no-signaling adversaries.

`@Article{ramanathan_single_2020, author = {Ramanathan, Ravishankar and Banacki, Michał and Rodríguez, Ricard Ravell and Horodecki, Paweł}, journal = {arXiv:2004.14782 [quant-ph]}, title = {Single trusted qubit is necessary and sufficient for quantum realisation of extremal no-signaling correlations}, year = {2020}, month = apr, note = {arXiv: 2004.14782}, abstract = {Quantum statistics can be considered from the perspective of postquantum no-signaling theories in which either none or only a certain number of quantum systems are trusted. In these scenarios, the role of states is played by the so-called no-signaling boxes or no-signaling assemblages respectively. It has been shown so far that in the usual Bell non-locality scenario with a single measurement run, quantum statistics can never reproduce an extremal non-local point within the set of no-signaling boxes. We provide here a general no-go rule showing that the latter stays true even if arbitrary sequential measurements are allowed. On the other hand, we prove a positive result showing that already a single trusted qubit is enough for quantum theory to produce a self-testable extremal point within the corresponding set of no-signaling assemblages. This result opens up the possibility for security proofs of cryptographic protocols against general no-signaling adversaries.}, groups = {Pawel_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2004.14782}, urldate = {2021-07-28}, }`

- Marcin Markiewicz, Mahasweta Pandit, and Wiesław Laskowski. Multiparameter estimation in generalized Mach-Zehnder interferometer.
*arXiv:2012.07645 [quant-ph]*, dec 2020. arXiv: 2012.07645

[BibTeX] [Abstract] [Download PDF]

In this work, we investigate the problem of multiphase estimation using generalized \$3\$- and \$4\$-mode Mach-Zehnder interferometer. In our setup, we assume that the number of unknown phases is the same as the number of modes in the interferometer, which introduces strong correlations between estimators of the phases. We show that despite these correlations and despite the lack of optimisation of a measurement strategy (a fixed interferometer is used) we can still obtain the Heisenberg-like scaling of precision of estimation of all the parameters. Our estimation scheme can be applied to the task of quantum-enhanced sensing in 3-dimensional interferometric configurations.

`@Article{markiewicz_multiparameter_2020, author = {Markiewicz, Marcin and Pandit, Mahasweta and Laskowski, Wiesław}, journal = {arXiv:2012.07645 [quant-ph]}, title = {Multiparameter estimation in generalized {Mach}-{Zehnder} interferometer}, year = {2020}, month = dec, note = {arXiv: 2012.07645}, abstract = {In this work, we investigate the problem of multiphase estimation using generalized \$3\$- and \$4\$-mode Mach-Zehnder interferometer. In our setup, we assume that the number of unknown phases is the same as the number of modes in the interferometer, which introduces strong correlations between estimators of the phases. We show that despite these correlations and despite the lack of optimisation of a measurement strategy (a fixed interferometer is used) we can still obtain the Heisenberg-like scaling of precision of estimation of all the parameters. Our estimation scheme can be applied to the task of quantum-enhanced sensing in 3-dimensional interferometric configurations.}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2012.07645}, urldate = {2021-07-28}, }`

- Łukasz Czekaj, Ana Belén Sainz, John Selby, and Michał Horodecki. Correlations constrained by composite measurements.
*arXiv:2009.04994 [quant-ph]*, sep 2020. arXiv: 2009.04994

[BibTeX] [Abstract] [Download PDF]

How to understand the set of correlations admissible in nature is one outstanding open problem in the core of the foundations of quantum theory. Here we take a complementary viewpoint to the device-independent approach, and explore the correlations that physical theories may feature when restricted by some particular constraints on their measurements. We show that demanding that a theory exhibits a composite measurement imposes a hierarchy of constraints on the structure of its sets of states and effects, which translate to a hierarchy of constraints on the allowed correlations themselves. We moreover focus on the particular case where one demands the existence of an entangled measurement that reads out the parity of local fiducial measurements. By formulating a non-linear Optimisation Problem, and semidefinite relaxations of it, we explore the consequences of the existence of such a parity reading measurement for violations of Bell inequalities. In particular, we show that in certain situations this assumption has surprisingly strong consequences, namely, that Tsirelson’s bound can be recovered.

`@Article{czekaj_correlations_2020, author = {Czekaj, Łukasz and Sainz, Ana Belén and Selby, John and Horodecki, Michał}, journal = {arXiv:2009.04994 [quant-ph]}, title = {Correlations constrained by composite measurements}, year = {2020}, month = sep, note = {arXiv: 2009.04994}, abstract = {How to understand the set of correlations admissible in nature is one outstanding open problem in the core of the foundations of quantum theory. Here we take a complementary viewpoint to the device-independent approach, and explore the correlations that physical theories may feature when restricted by some particular constraints on their measurements. We show that demanding that a theory exhibits a composite measurement imposes a hierarchy of constraints on the structure of its sets of states and effects, which translate to a hierarchy of constraints on the allowed correlations themselves. We moreover focus on the particular case where one demands the existence of an entangled measurement that reads out the parity of local fiducial measurements. By formulating a non-linear Optimisation Problem, and semidefinite relaxations of it, we explore the consequences of the existence of such a parity reading measurement for violations of Bell inequalities. In particular, we show that in certain situations this assumption has surprisingly strong consequences, namely, that Tsirelson's bound can be recovered.}, groups = {Michal_H}, keywords = {Quantum Physics}, url = {http://arxiv.org/abs/2009.04994}, urldate = {2021-07-28}, }`

- Aaron Z. Goldberg, Pablo de la Hoz, Gunnar Bjork, Andrei B. Klimov, Markus Grassl, Gerd Leuchs, and Luis L. Sanchez-Soto. Quantum concepts in optical polarization.
*arXiv:2011.03979 [quant-ph]*, nov 2020. arXiv: 2011.03979

[BibTeX] [Abstract] [Download PDF]

We comprehensively review the quantum theory of the polarization properties of light. In classical optics, these traits are characterized by the Stokes parameters, which can be geometrically interpreted using the Poincar\textbackslash’e sphere. Remarkably, these Stokes parameters can also be applied to the quantum world, but then important differences emerge: now, because fluctuations in the number of photons are unavoidable, one is forced to work in the three-dimensional Poincar\textbackslash’e space that can be regarded as a set of nested spheres. Additionally, higher-order moments of the Stokes variables might play a substantial role for quantum states, which is not the case for most classical Gaussian states. This brings about important differences between these two worlds that we review in detail. In particular, the classical degree of polarization produces unsatisfactory results in the quantum domain. We compare alternative quantum degrees and put forth that they order various states differently. Finally, intrinsically nonclassical states are explored and their potential applications in quantum technologies are discussed.

`@article{goldberg_quantum_2020, title = {Quantum concepts in optical polarization}, url = {http://arxiv.org/abs/2011.03979}, abstract = {We comprehensively review the quantum theory of the polarization properties of light. In classical optics, these traits are characterized by the Stokes parameters, which can be geometrically interpreted using the Poincar{\textbackslash}'e sphere. Remarkably, these Stokes parameters can also be applied to the quantum world, but then important differences emerge: now, because fluctuations in the number of photons are unavoidable, one is forced to work in the three-dimensional Poincar{\textbackslash}'e space that can be regarded as a set of nested spheres. Additionally, higher-order moments of the Stokes variables might play a substantial role for quantum states, which is not the case for most classical Gaussian states. This brings about important differences between these two worlds that we review in detail. In particular, the classical degree of polarization produces unsatisfactory results in the quantum domain. We compare alternative quantum degrees and put forth that they order various states differently. Finally, intrinsically nonclassical states are explored and their potential applications in quantum technologies are discussed.}, urldate = {2021-07-28}, journal = {arXiv:2011.03979 [quant-ph]}, author = {Goldberg, Aaron Z. and de la Hoz, Pablo and Bjork, Gunnar and Klimov, Andrei B. and Grassl, Markus and Leuchs, Gerd and Sanchez-Soto, Luis L.}, month = nov, year = {2020}, note = {arXiv: 2011.03979}, keywords = {Quantum Physics}, }`

- B. Ahmadi, S. Salimi, and A. S. Khorashad. No Entropy Production in Quantum Thermodynamics.
*arXiv:2002.10747 [quant-ph]*, feb 2020. arXiv: 2002.10747

[BibTeX] [Abstract] [Download PDF]

In this work we will show that there exists a fundamental difference between microscopic quantum thermodynamics and macroscopic classical thermodynamics. It will be proved that the entropy production in quantum thermodynamics always vanishes for both closed and open quantum thermodynamic systems. This novel and very surprising result is derived based on the genuine reasoning Clausius used to establish the science of thermodynamics in the first place. This result will interestingly lead to define the generalized temperature for any non-equilibrium quantum system.

`@article{ahmadi_no_2020, title = {No {Entropy} {Production} in {Quantum} {Thermodynamics}}, url = {http://arxiv.org/abs/2002.10747}, abstract = {In this work we will show that there exists a fundamental difference between microscopic quantum thermodynamics and macroscopic classical thermodynamics. It will be proved that the entropy production in quantum thermodynamics always vanishes for both closed and open quantum thermodynamic systems. This novel and very surprising result is derived based on the genuine reasoning Clausius used to establish the science of thermodynamics in the first place. This result will interestingly lead to define the generalized temperature for any non-equilibrium quantum system.}, urldate = {2021-07-28}, journal = {arXiv:2002.10747 [quant-ph]}, author = {Ahmadi, B. and Salimi, S. and Khorashad, A. S.}, month = feb, year = {2020}, note = {arXiv: 2002.10747}, keywords = {Quantum Physics}, }`

- Siddhartha Das, Stefan Bäuml, Marek Winczewski, and Karol Horodecki. Universal limitations on quantum key distribution over a network.
*arXiv:1912.03646 [quant-ph]*, sep 2020. arXiv: 1912.03646

[BibTeX] [Abstract] [Download PDF]

The possibility to achieve secure communication among trusted parties by means of the quantum entanglement is intriguing both from a fundamental and an application purpose. In this work, we show that any state (after distillation) from which a quantum secret key can be obtained by local measurements has to be genuinely multipartite entangled. We introduce the most general form of memoryless network quantum channel: quantum multiplex channels. We define and determine asymptotic and non-asymptotic LOCC assisted conference key agreement capacities for quantum multiplex channels and provide various strong and weak converse bounds in terms of the divergence based entanglement measures of the quantum multiplex channels. The structure of our protocol manifested by an adaptive strategy of secret key and entanglement (GHZ state) distillation over an arbitrary multiplex quantum channel is generic. In particular, it provides a universal framework to study the performance of quantum key repeaters and – for the first time – of the MDI-QKD setups of channels. For teleportation-covariant multiplex quantum channels, which are channels with certain symmetries, we get upper bounds on the secret key agreement capacities in terms of the entanglement measures of their Choi states. For some network prototypes of practical relevance, we evaluate upper bounds on the conference key agreement capacities and MDI-QKD capacities. Upper bounds on the LOCC-assisted conference key agreement rates are also upper bounds on the distillation rates of GHZ states, a class of genuinely entangled pure states. We also obtain bounds on the rates at which conference key and GHZ states can be distilled from a finite number of copies of an arbitrary multipartite quantum state. Using our bounds, in particular cases, we are able to determine the capacities for quantum key distribution channels and rates of GHZ-state distillation.

`@article{arXiv_das_universal_2020, title = {Universal limitations on quantum key distribution over a network}, url = {http://arxiv.org/abs/1912.03646}, abstract = {The possibility to achieve secure communication among trusted parties by means of the quantum entanglement is intriguing both from a fundamental and an application purpose. In this work, we show that any state (after distillation) from which a quantum secret key can be obtained by local measurements has to be genuinely multipartite entangled. We introduce the most general form of memoryless network quantum channel: quantum multiplex channels. We define and determine asymptotic and non-asymptotic LOCC assisted conference key agreement capacities for quantum multiplex channels and provide various strong and weak converse bounds in terms of the divergence based entanglement measures of the quantum multiplex channels. The structure of our protocol manifested by an adaptive strategy of secret key and entanglement (GHZ state) distillation over an arbitrary multiplex quantum channel is generic. In particular, it provides a universal framework to study the performance of quantum key repeaters and - for the first time - of the MDI-QKD setups of channels. For teleportation-covariant multiplex quantum channels, which are channels with certain symmetries, we get upper bounds on the secret key agreement capacities in terms of the entanglement measures of their Choi states. For some network prototypes of practical relevance, we evaluate upper bounds on the conference key agreement capacities and MDI-QKD capacities. Upper bounds on the LOCC-assisted conference key agreement rates are also upper bounds on the distillation rates of GHZ states, a class of genuinely entangled pure states. We also obtain bounds on the rates at which conference key and GHZ states can be distilled from a finite number of copies of an arbitrary multipartite quantum state. Using our bounds, in particular cases, we are able to determine the capacities for quantum key distribution channels and rates of GHZ-state distillation.}, urldate = {2021-07-28}, journal = {arXiv:1912.03646 [quant-ph]}, author = {Das, Siddhartha and Bäuml, Stefan and Winczewski, Marek and Horodecki, Karol}, month = sep, year = {2020}, note = {arXiv: 1912.03646}, keywords = {Quantum Physics, Computer Science - Information Theory}, }`

- Wooyeong Song, Marcin Wieśniak, Nana Liu, Marcin Pawłowski, Jinhyoung Lee, Jaewan Kim, and Jeongho Bang. Tangible Reduction of Sample Complexity with Large Classical Samples and Small Quantum System.
*arXiv:1905.05751 [quant-ph]*, jun 2020. arXiv: 1905.05751

[BibTeX] [Abstract] [Download PDF]

Quantum computation requires large classical datasets to be embedded into quantum states in order to exploit quantum parallelism. However, this embedding requires considerable resources. It would therefore be desirable to avoid it, if possible, for noisy intermediate-scale quantum (NISQ) implementation. Accordingly, we consider a classical-quantum hybrid architecture, which allows large classical input data, with a relatively small-scale quantum system. This hybrid architecture is used to implement an oracle. It is shown that in the presence of noise in the hybrid oracle, the effects of internal noise can cancel each other out and thereby improve the query success rate. It is also shown that such an immunity of the hybrid oracle to noise directly and tangibly reduces the sample complexity in the probably-approximately-correct learning framework. This NISQ-compatible learning advantage is attributed to the oracle’s ability to handle large input features.

`@article{song_tangible_2020, title = {Tangible {Reduction} of {Sample} {Complexity} with {Large} {Classical} {Samples} and {Small} {Quantum} {System}}, url = {http://arxiv.org/abs/1905.05751}, abstract = {Quantum computation requires large classical datasets to be embedded into quantum states in order to exploit quantum parallelism. However, this embedding requires considerable resources. It would therefore be desirable to avoid it, if possible, for noisy intermediate-scale quantum (NISQ) implementation. Accordingly, we consider a classical-quantum hybrid architecture, which allows large classical input data, with a relatively small-scale quantum system. This hybrid architecture is used to implement an oracle. It is shown that in the presence of noise in the hybrid oracle, the effects of internal noise can cancel each other out and thereby improve the query success rate. It is also shown that such an immunity of the hybrid oracle to noise directly and tangibly reduces the sample complexity in the probably-approximately-correct learning framework. This NISQ-compatible learning advantage is attributed to the oracle's ability to handle large input features.}, urldate = {2021-07-28}, journal = {arXiv:1905.05751 [quant-ph]}, author = {Song, Wooyeong and Wieśniak, Marcin and Liu, Nana and Pawłowski, Marcin and Lee, Jinhyoung and Kim, Jaewan and Bang, Jeongho}, month = jun, year = {2020}, note = {arXiv: 1905.05751}, keywords = {Quantum Physics}, }`

- Omer Sakarya, Marek Winczewski, Adam Rutkowski, and Karol Horodecki. $^*$Hybrid quantum network design against unauthorized secret-key generation, and its memory cost.
*Physical Review Research*, 2(4), oct 2020. doi:10.1103/physrevresearch.2.043022

[BibTeX] [Download PDF]`@article{arXiv_Sakarya_2020, doi = {10.1103/physrevresearch.2.043022}, url = {https://doi.org/10.1103%2Fphysrevresearch.2.043022}, year = 2020, month = oct, publisher = {American Physical Society ({APS})}, volume = {2}, number = {4}, author = {Omer Sakarya and Marek Winczewski and Adam Rutkowski and Karol Horodecki}, title = {$^*$Hybrid quantum network design against unauthorized secret-key generation, and its memory cost}, journal = {Physical Review Research} }`

- Edgar A. Aguilar, Hanna Wojewódka-Ściążko, Maciej Stankiewicz, Christopher Perry, Piotr Ćwikliński, Andrzej Grudka, Karol Horodecki, and Michał Horodecki. Thermal Operations in general are not memoryless. , 2020. doi:10.48550/ARXIV.2009.03110

[BibTeX] [Download PDF]`@article{https://doi.org/10.48550/arxiv.2009.03110, doi = {10.48550/ARXIV.2009.03110}, url = {https://arxiv.org/abs/2009.03110}, author = {Aguilar, Edgar A. and Wojewódka-Ściążko, Hanna and Stankiewicz, Maciej and Perry, Christopher and Ćwikliński, Piotr and Grudka, Andrzej and Horodecki, Karol and Horodecki, Michał}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Thermal Operations in general are not memoryless}, publisher = {arXiv}, year = {2020}, copyright = {arXiv.org perpetual, non-exclusive license} }`

### 2019

- Paul Skrzypczyk, Matty J. Hoban, Ana Belén Sainz, and Noah Linden. Complexity of compatible measurements.
*arXiv:1908.10085 [quant-ph]*, 2019.

[BibTeX]`@article{skrzypczyk2020complexity, title={Complexity of compatible measurements}, author={Skrzypczyk, Paul and Hoban, Matty J and Sainz, Ana Bel{\'e}n and Linden, Noah}, journal={arXiv:1908.10085 [quant-ph]}, year={2019} }`

- Sandu Popescu, Ana Belén Sainz, Anthony J. Short, and Andreas Winter. Reference frames which separately store non-commuting conserved quantities.
*arXiv:1908.02713 [quant-ph]*, 2019.

[BibTeX]`@article{popescu2019reference, title={Reference frames which separately store non-commuting conserved quantities}, author={Popescu, Sandu and Sainz, Ana Bel{\'e}n and Short, Anthony J and Winter, Andreas}, journal={arXiv:1908.02713 [quant-ph]}, year={2019} }`

- Ana Belén Sainz, Matty J. Hoban, Paul Skrzypczyk, and Leandro Aolita. Bipartite post-quantum steering in generalised scenarios.
*arXiv:1907.03705 [quant-ph]*, 2019.

[BibTeX]`@article{sainz2019bipartite, title={Bipartite post-quantum steering in generalised scenarios}, author={Sainz, Ana Bel{\'e}n and Hoban, Matty J and Skrzypczyk, Paul and Aolita, Leandro}, journal={arXiv:1907.03705 [quant-ph]}, year={2019} }`

- Elie Wolfe, David Schmid, Ana Belén Sainz, Ravi Kunjwal, and Robert W. Spekkens. Quantifying Bell: the Resource Theory of Nonclassicality of Common-Cause Boxes.
*arXiv:1903.06311 [quant-ph]*, 2019.

[BibTeX]`@article{wolfe2019quantifying, title={Quantifying Bell: the Resource Theory of Nonclassicality of Common-Cause Boxes}, author={Wolfe, Elie and Schmid, David and Sainz, Ana Bel{\'e}n and Kunjwal, Ravi and Spekkens, Robert W}, journal={arXiv:1903.06311 [quant-ph]}, year={2019} }`

- Michał Eckstein and Paweł Horodecki. The experiment paradox in physics.
*arXiv:1904.04117 [gr-qc, physics:hep-th, physics:physics, physics:quant-ph]*, apr 2019. arXiv: 1904.04117

[BibTeX] [Abstract] [Download PDF]

Modern physics is founded on two mainstays: mathematical modelling and empirical verification. These two assumptions are prerequisite for the objectivity of scientific discourse. Here we show, however, that they are contradictory, leading to the `experiment paradox’. We reveal that any experiment performed on a physical system is – by necessity – invasive and thus establishes inevitable limits to the accuracy of any mathematical model. We track its manifestations in both classical and quantum physics and show how it is overcome `in practice’ via the concept of environment. We argue that the scientific pragmatism ordains two methodological principles of compressibility and stability.

`@Article{eckstein_experiment_2019, author = {Eckstein, Michał and Horodecki, Paweł}, journal = {arXiv:1904.04117 [gr-qc, physics:hep-th, physics:physics, physics:quant-ph]}, title = {The experiment paradox in physics}, year = {2019}, month = apr, note = {arXiv: 1904.04117}, abstract = {Modern physics is founded on two mainstays: mathematical modelling and empirical verification. These two assumptions are prerequisite for the objectivity of scientific discourse. Here we show, however, that they are contradictory, leading to the `experiment paradox'. We reveal that any experiment performed on a physical system is - by necessity - invasive and thus establishes inevitable limits to the accuracy of any mathematical model. We track its manifestations in both classical and quantum physics and show how it is overcome `in practice' via the concept of environment. We argue that the scientific pragmatism ordains two methodological principles of compressibility and stability.}, groups = {Pawel_H}, keywords = {Physics - History and Philosophy of Physics, General Relativity and Quantum Cosmology, High Energy Physics - Theory, Physics - Classical Physics, Quantum Physics}, url = {http://arxiv.org/abs/1904.04117}, urldate = {2021-07-28}, }`

- Sumit Rout, Ananda G. Maity, Amit Mukherjee, Saronath Halder, and Manik Banik. Multiparty orthogonal product states with minimal genuine nonlocality.
*arXiv:1910.14308 [quant-ph]*, oct 2019.

[BibTeX] [Abstract] [Download PDF]

Nonlocality without entanglement and its subsequent generalizations offer deep information-theoretic insights and subsequently find several useful applications. Concept of genuinely nonlocal set of product states emerges as a natural multipartite generalization of this phenomenon. Existence of such sets eventually motivates the problem concerning their entanglement-assisted discrimination. Here, we construct examples of genuinely nonlocal product states for arbitrary number of parties. Strength of genuine nonlocality of these sets can be considered minimal as their perfect discrimination is possible with entangled resources residing in Hilbert spaces having the smallest possible dimensions. Our constructions lead to fully separable measurements that are impossible to implement even if all but one party come together. Furthermore, they also provide the opportunity to compare different multipartite states that otherwise are incomparable under single copy local manipulation.

`@Article{Rout2019, author = {Sumit Rout and Ananda G. Maity and Amit Mukherjee and Saronath Halder and Manik Banik}, journal = {arXiv:1910.14308 [quant-ph]}, title = {Multiparty orthogonal product states with minimal genuine nonlocality}, year = {2019}, month = oct, abstract = {Nonlocality without entanglement and its subsequent generalizations offer deep information-theoretic insights and subsequently find several useful applications. Concept of genuinely nonlocal set of product states emerges as a natural multipartite generalization of this phenomenon. Existence of such sets eventually motivates the problem concerning their entanglement-assisted discrimination. Here, we construct examples of genuinely nonlocal product states for arbitrary number of parties. Strength of genuine nonlocality of these sets can be considered minimal as their perfect discrimination is possible with entangled resources residing in Hilbert spaces having the smallest possible dimensions. Our constructions lead to fully separable measurements that are impossible to implement even if all but one party come together. Furthermore, they also provide the opportunity to compare different multipartite states that otherwise are incomparable under single copy local manipulation.}, archiveprefix = {arXiv}, eprint = {1910.14308}, keywords = {quant-ph}, primaryclass = {quant-ph}, url = {https://arxiv.org/pdf/1910.14308}, }`

- Marek Winczewski, Tamoghna Das, and Karol Horodecki. Limitations on device independent key secure against non signaling adversary via the squashed non-locality. , 2019. doi:10.48550/ARXIV.1903.12154

[BibTeX] [Download PDF]`@article{arXiv_NSDI_MW_TD_KH, doi = {10.48550/ARXIV.1903.12154}, url = {https://arxiv.org/abs/1903.12154}, author = {Winczewski, Marek and Das, Tamoghna and Horodecki, Karol}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Limitations on device independent key secure against non signaling adversary via the squashed non-locality}, publisher = {arXiv}, year = {2019}, copyright = {arXiv.org perpetual, non-exclusive license} }`

### 2018

- Thomas Van Himbeeck, Jonatan Bohr Brask, Stefano Pironio, Ravishankar Ramanathan, Ana Belén Sainz, and Elie Wolfe. Quantum violations in the Instrumental scenario and their relations to the Bell scenario.
*arXiv:1804.04119 [quant-ph]*, 2018.

[BibTeX]`@article{van2018quantum, title={Quantum violations in the Instrumental scenario and their relations to the Bell scenario}, author={Van Himbeeck, Thomas and Brask, Jonatan Bohr and Pironio, Stefano and Ramanathan, Ravishankar and Sainz, Ana Bel{\'e}n and Wolfe, Elie}, journal={arXiv:1804.04119 [quant-ph]}, year={2018} }`

- Marek Winczewski, Tamoghna Das, John H. Selby, Karol Horodecki, Paweł Horodecki, Łukasz Pankowski, Marco Piani, and Ravishankar Ramanathan. Complete extension: the non-signaling analog of quantum purification. , 2018. doi:10.48550/ARXIV.1810.02222

[BibTeX] [Download PDF]`@article{arXiv_complete_extension, doi = {10.48550/ARXIV.1810.02222}, url = {https://arxiv.org/abs/1810.02222}, author = {Winczewski, Marek and Das, Tamoghna and Selby, John H. and Horodecki, Karol and Horodecki, Paweł and Pankowski, Łukasz and Piani, Marco and Ramanathan, Ravishankar}, keywords = {Quantum Physics (quant-ph), FOS: Physical sciences, FOS: Physical sciences}, title = {Complete extension: the non-signaling analog of quantum purification}, publisher = {arXiv}, year = {2018}, copyright = {arXiv.org perpetual, non-exclusive license} }`