Leader of the research group: Marek Żukowski

Post-docs: Tamoghna Das, Antonio Mandarino

PhD students: Bianka Wołoncewicz, Konrad Schlichtholz

The broad aim of the Multiphoton Quantum Optics for Quantum Information Group is to develop theoretical quantum information science of immediate experimental testability as well as to study the fundamental issues like causality, new concepts in theoretical quantum optics, and efficiency of quantum (optical) protocols.

Activity

Specific goals include:
– Operational translation of the schemes prosed by the other groups of ICTQT into experimental optical setups and feasibility studies.
– Direct collaboration with experimental teams of our IQOQI partner as well as other laboratories.
– Investigations concerning device-independent or self-testing quantum communication, quantum information processing schemes, aimed at commercialization.
– Search for new research avenues in quantum optics allowing demonstrations of quantum protocols or various kinds.
– New indicators of non-classicality in quantum optics.
– Application of theoretical/operational/experimental methods of quantum multiphoton interferometry to other processes of potential value for quantum communication and information processing.
– Quantum optical implementations of secure data transmission.
– Theory of optical test of quantum mechanics.

Publications

2021

  1. 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},
    }
  2. 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):42226, 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},
    }
  3. 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):73042, 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},
    }

2020

  1. 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, {\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

    @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},
    }
  2. Saptarshi Roy, Tamoghna Das, and Aditi Sen(De). Computable genuine multimode entanglement measure: Gaussian versus non-Gaussian. Physical Review A, 102(1):12421, 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},
    }

2019

  1. 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):32041, 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},
    }
  2. 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

  1. 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):93006, 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

2021

  1. 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], 2021. arXiv: 2102.03254
    [BibTeX] [Abstract] [Download PDF]

    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.

    @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},
    }
  2. 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 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?},
    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]},
    author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Woloncewicz, Bianka and Żukowski, Marek},
    month = feb,
    year = {2021},
    note = {arXiv: 2102.06689},
    keywords = {Quantum Physics},
    }
  3. 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},
    }
  4. 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},
    }
  5. Tamoghna Das, Marcin Karczewski, Antonio Mandarino, Marcin Markiewicz, and Marek Żukowski. Optimal interferometry for Bell-nonclassicality by a vacuum–one-photon qubit. Arxiv e-prints, pages arXiv:2109.10170, sep 2021.
    [BibTeX] [Abstract] [Download PDF]

    We show how to robustly violate local realism within the weak$-$field homodyne measurement scheme for any superposition of one photon with vacuum. Our setup involves tunable beamsplitters at the measurement stations, and the local oscillator fields significantly varying between the settings. As photon number resolving measurements are now feasible, we advocate for the use of the Clauser$-$Horne Bell inequalities for detection events using precisely defined numbers of photons. We find a condition for optimal measurement settings for the maximal violation of the Clauser-Horne inequality with weak-field homodyne detection, which states that the reflectivity of the local beamsplitter must be equal to the strength of the local oscillator field. We show that this condition holds not only for the vacuum$–$one$-$photon qubit input state, but also for the Two$-$Mode Squeezed Vacuum state, which suggests its generality as a property of weak$-$field homodyne detection with photon- number resolution. Our findings suggest a possible path to employ such scenarios in device$-$independent quantum protocols.

    @Article{Das2021,
    author = {Das, Tamoghna and Karczewski, Marcin and Mandarino, Antonio and Markiewicz, Marcin and Żukowski, Marek},
    journal = {arXiv e-prints},
    title = {Optimal interferometry for {B}ell-nonclassicality by a vacuum--one-photon qubit},
    year = {2021},
    month = sep,
    pages = {arXiv:2109.10170},
    abstract = {We show how to robustly violate local realism within the weak$-$field homodyne measurement scheme for any superposition of one photon with vacuum. Our setup involves tunable beamsplitters at the measurement stations, and the local oscillator fields significantly varying between the settings. As photon number resolving measurements are now feasible, we advocate for the use of the Clauser$-$Horne Bell inequalities for detection events using precisely defined numbers of photons. We find a condition for optimal measurement settings for the maximal violation of the Clauser-Horne inequality with weak-field homodyne detection, which states that the reflectivity of the local beamsplitter must be equal to the strength of the local oscillator field. We show that this condition holds not only for the vacuum$--$one$-$photon qubit input state, but also for the Two$-$Mode Squeezed Vacuum state, which suggests its generality as a property of weak$-$field homodyne detection with photon- number resolution. Our findings suggest a possible path to employ such scenarios in device$-$independent quantum protocols.},
    archiveprefix = {arXiv},
    eid = {arXiv:2109.10170},
    eprint = {2109.10170},
    keywords = {Quantum {P}hysics},
    primaryclass = {quant-ph},
    url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210910170D},
    }
  6. 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},
    }

Group members

Get to know the people behind ICTQT.
prof. dr hab. Marek Żukowski

prof. dr hab. Marek Żukowski

Group Leader

marek.zukowski@ug.edu.pl

dr Antonio Mandarino

dr Antonio Mandarino

Post Doc

antonio.mandarino@ug.edu.pl

dr Tamoghna Das

dr Tamoghna Das

Post Doc

tamoghna.das@ug.edu.pl

mgr Bianka Wołoncewicz

mgr Bianka Wołoncewicz

PhD student

bianka.woloncewicz@phdstud.ug.edu.pl

mgr Konrad Schlichtholz

mgr Konrad Schlichtholz

PhD student

konrad.schlichtholz@phdstud.ug.edu.pl

Former members

Keywords: quantum optics, multiphoton interferometry, reduction of communication complexity, foundations of quantum physics, quantum information,  Bell’s theorem, quantum optical circuits.