# Past events

Thursday, September 24th, 2020, 16:00

Speaker: Ana Belén Sainz

from ICTQT
title: Bipartite post-quantum steering in generalised scenarios
Abstract: The study of stronger-than-quantum effects is a fruitful line of research that provides valuable insight into quantum theory. Unfortunately, traditional bipartite steering scenarios can always be explained by quantum theory. Here we show that, by relaxing this traditional setup, bipartite steering incompatible with quantum theory is possible. The two scenarios we describe, which still feature Alice remotely steering Bob’s system, are: (i) one where Bob also has an input and operates on his subsystem, and (ii) the instrumental steering’ scenario. We show that such bipartite post-quantum steering is a genuinely new type of post-quantum nonlocality, which does not follow from post-quantum Bell nonlocality. In addition, we present a method to bound quantum violations of steering inequalities in these scenarios. [Phys. Rev. Lett. 125, 050404 (2020) — arXiv:1907.03705].
seminar organised by: Quantum Information and Quantum Computing Working Group of Center for Theoretical Physics of the Polish Academy of Sciences (CTP PAS)

Thursday, September 10, 2020, 14:00
Speaker: Ninnat Dangniam
from Fudan University
title: Optimal verification of stabilizer states
seminar organised by: Quantum Information and Quantum Computing Working Group of Center for Theoretical Physics of the Polish Academy of Sciences (CTP PAS)

July 29th, 2020 at 2:00 pm

Speaker: Manik Banik,
from Indian Institute of Science Education and Research (Thiruvananthapuram)
Title: Bell Nonlocality and the Reality of Quantum Wavefunction

Abstract:

Status of quantum wavefunction is one of the most debated issues in quantum foundations — whether it corresponds directly to the reality or just represents knowledge or information about some aspect of reality. In this work we propose a  ψ-ontology theorem addressing this question. Our theorem invokes an assumption, called ‘no ontic retro-causality’, about the underlying ontological model. We provide physical rationale for this assumption and discuss novelty of the present theorem over the existing ones. At the core of our derivation we utilize another seminal no-go result by John S. Bell that rules out any it local realistic world view for quantum theory. We show that Bell nonlocality excludes the ontological explanations where quantum wavefunction is treated as mere information, viz. the ψ-epistemic explanations. In fact, models even with some degree of epistemicity can not fully incorporate the phenomena of Bell nonlocality observed in quantum theory.

June 24th, 2020 at 2:00 pm

Speaker: Victoria Wright,
from ICTQT
Title: General Probabilistic Theories with a Gleason-type Theorem

Abstract:

General probabilistic theories are shown to admit a Gleason-type theorem if and only if they satisfy the no-restriction hypothesis, or a “noisy” version of the hypothesis. Therefore, in precisely these theories we recover the state space by assuming that (i) states consistently assign probabilities to measurement outcomes and (ii) there is a unique state for every such assignment.

May 13th, 2020 at 2:00 pm

Speaker: Gláucia Murta,
from Heinrich-Heine-Universität Düsseldorf, Germany
Title: Device-independent quantum cryptography in the multipartite scenario

Abstract:
Going beyond the simple two-party scenario of quantum key distribution, we consider N parties who wish to certify security against a potential eavesdropper in a cryptographic task. Moreover, we consider the very adversarial scenario in which the parties make no assumption about the underlying quantum system or the internal working of their measurement devices. This is the device-independent scenario. In the device-independent scenario, security is certified by the violation of a Bell inequality. In this talk I will present our recent results on bounds on Eve’s uncertainty as a function of the violation of the multipartite MABK Bell inequality. I will discuss the implication of these results to cryptographic tasks, such as randomness expansion and conference key agreement. Finally, I discuss the challenges and possibilities to extend our results to other Bell inequalities, which can lead to better cryptographic protocols.

April 22, 2020 at 2:00 pm

Seminar given by Patryk Lipka-Bartosik
University of Bristol, UK
Title: Operational advantages provided by nonclassical teleportation

Abstract:
The standard benchmark for teleportation is the average fidelity of teleportation and according to this benchmark not all states are useful for teleportation. It was recently shown, however, that all entangled states lead to nonclassical teleportation, with there being no classical scheme able to reproduce the states teleported to Bob. Here we study the operational significance of this result. On the one hand, we demonstrate that every state is useful for teleportation if a generalization of the average fidelity of teleportation is considered which concerns teleporting quantum correlations. On the other hand, we show the strength of a particular entangled state and entangled measurement for teleportation—as quantified by the robustness of teleportation—precisely characterizes their ability to offer an advantage in the task of subchannel discrimination with side information. This connection allows us to prove that every entangled state outperforms all separable states when acting as a quantum memory in this discrimination task. Finally, within the context of a resource theory of teleportation, we show that the two operational tasks considered provide complete sets of monotones for two partial orders based on the notion of teleportation simulation, one classical and one quantum.

March 27, 2020 at 12:00

Seminar given by Steven Bass
Kitzbühel Centre for Physics, Austria / Jagiellonian University in Krakow, Poland
Title: The Cosmological Constant Puzzle – Symmetries of Quantum Fluctuations

Abstract:
The cosmological constant in Einstein’s equations of General Relativity is a prime candidate to describe the dark energy that drives the accelerating expansion of the Universe and which contributes 69% of its energy budget. The cosmological constant measures the energy density of the vacuum perceived by gravitation. Experimentally, it is characterised by a tiny energy scale 0.002 eV. How should we understand this ? The quantum vacuum is described by particle physics where the mass scales that enter are very much larger. If one naively sums the zero-point energies of quantum fluctuations up to the energies where we do collider experiments at CERN then the cosmological constant comes out 10^60 times too large. Here we argue that the tiny value of the cosmological constant may be telling us something deep about the origin of symmetry in the subatomic world. The gauge symmetries which describe particle interactions may be emergent. The presentation will be given at Colloquium level and suitable for good Masters students.

May 6th, 2020 at 2:00 pm CET

Seminar given by David Schmid
University of Waterloo / Perimeter Institute, Canada
Title: Why standard entanglement theory is inappropriate for the study of Bell scenarios

Abstract:
A standard approach to quantifying resources is to determine which operations on the resources are freely available and to deduce the ordering relation among the resources that these operations induce. If the resource of interest is the nonclassicality of the correlations embodied in a quantum state, that is, entanglement, then it is typically presumed that the appropriate choice of free operations is local operations and classical communication (LOCC). We here argue that, in spite of the near-universal endorsement of the LOCC paradigm by the quantum information community, this is the wrong choice for one of the most prominent applications of entanglement theory, namely, the study of Bell scenarios. The nonclassicality of correlations in such scenarios, we argue, should be quantified instead by local operations and shared randomness (LOSR). We support this thesis by showing that various perverse features of the interplay between entanglement and nonlocality are merely an artifact of the use of LOCC-entanglement and that the interplay between LOSR-entanglement and nonlocality is natural and intuitive. Specifically, we show that the LOSR paradigm (i) provides a resolution of the “anomaly of nonlocality”, wherein partially entangled states exhibit more nonlocality than maximally entangled states, (ii) entails a notion of genuine multipartite entanglement that is distinct from the conventional one and which is free of several of its pathological features, and (iii) makes possible a resource-theoretic account of the self-testing of entangled states which simplifies and generalizes 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.

April 24, 2020 at 2:00 pm

Seminar given by Jan Tuziemski
Stockholm University, Sweden
Title: Out-of-time-ordered correlation functions in open systems

Abstract:
Recent theoretical and experimental studies have shown significance of quantum information scrambling for problems encountered in high-energy physics, quantum information, and condensed matter. Due to complexity of quantum many-body systems it is plausible that new developments in this field will be achieved by experimental explorations. Therefore, a better theoretical understanding of quantum information scrambling in systems affected by noise is needed. To address this problem I will discuss indicators of quantum scrambling – out-of-time-ordered correlation functions (OTOCs) in open quantum systems. As most experimental protocols for measuring OTOCs are based on backward time evolution, two possible scenarios of joint system-environment dynamics reversal will be considered. Derivation of general formulas for OTOCs in those cases as well as a study of the spin chain model coupled to the environment of harmonic oscillators will be presented.

April 22, 2020 at 2:00 pm

Seminar given by Patryk Lipka-Bartosik
University of Bristol, UK
Title: Operational advantages provided by nonclassical teleportation

Abstract:
The standard benchmark for teleportation is the average fidelity of teleportation and according to this benchmark not all states are useful for teleportation. It was recently shown, however, that all entangled states lead to nonclassical teleportation, with there being no classical scheme able to reproduce the states teleported to Bob. Here we study the operational significance of this result. On the one hand, we demonstrate that every state is useful for teleportation if a generalization of the average fidelity of teleportation is considered which concerns teleporting quantum correlations. On the other hand, we show the strength of a particular entangled state and entangled measurement for teleportation—as quantified by the robustness of teleportation—precisely characterizes their ability to offer an advantage in the task of subchannel discrimination with side information. This connection allows us to prove that every entangled state outperforms all separable states when acting as a quantum memory in this discrimination task. Finally, within the context of a resource theory of teleportation, we show that the two operational tasks considered provide complete sets of monotones for two partial orders based on the notion of teleportation simulation, one classical and one quantum.

February 12, 2020 at 10:15

Seminar given by Fattah Sakuldee
ICTQT, UG, Poland
Title: Kolmogorov consistency as a quantumness witness for external system

Abstract:
We study the classicality of a finite quantum system, called environment, defined by commutativity of the associate operator algebra, given sequential measurements on the environment. We demonstrate by constructing a scheme of probing from the pure-dephasing-type interaction with a qudit and preparation-evolution-measurement protocol thereon, the weak measurement sequence on the studied environment can be induced and some characteristics of the environment can be extracted from measurement statistics. From the general measurements on the environment, we consider its Kolmogorov consistency, the situation when a shorter length joint probability can be extracted from the longer one by summing the missing all possible intermediate outcomes.
We provide general criteria for equivalence between Kolmogorov consistency of the statistics for arbitrary measurements and commutativity property of operator algebra of the environment and apply the criteria to show explicitly for the induced measurements. As a result, we show that Kolmogorov consistency of the probability can be considered as a quantumness witness for its corresponding operator algebra of the environment if the conditional Hamiltonians are all non-degenerate. For the qubit, the equivalence can be obtained in general if one considers two axes of measurements namely X and Y.

Place: Faculty of Mathematics, Physics and Computer Science, Wita Stwosza 59, Gdansk, room no. 361 (IFTiA).

February 7, 2020 at 12:15

Seminar given by Stefano Cusumano
NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR (Pisa), Italy
Title: Open quantum systems and potential engineering

Abstract:
As I will shortly move to ICTQT, in this talk I will try to give an overview of my work during the PhD. During this period I worked mainly on open quantum systems, applying collisional models to study both cascade systems (i.e. systems with a chiral propagation of information) and thermodynamic problems. On the other side, I also worked on potential engineering, that is, the design of potential profiles in order to obtain quantum states with specific properties or to perform specific tasks.

Place: Faculty of Mathematics, Physics and Computer Science, Wita Stwosza 59, Gdansk, room no. 361 (IFTiA).

February 5, 2020 at 10:15

Seminar given by Dominic Horsman
Université Grenoble Alpes, France
Title: Quantum compilation using the ZX-calculus

Abstract:
In this talk I will give an introduction to the use of the ZX calculus of observables as a compilation language for quantum computing.
ZX calculus diagrams comprise a formal re-write language that allows purely diagrammatic equational reasoning for qubit quantum mechanics. I will give a basic introduction to the diagrams (no category theory required), and show how the calculus is especially suited to acting as an ‘intermediate representation’ for quantum compilers. This entails mediating between high-level user workloads/algorithms and qubit-level device specifications. I will go over recent work (both academic and commercial) on circuit optimisation using the calculus, and on its function as design, verification, and optimisation language for error correction. I will finish by discussing insights the use of ZX gives into possible new models of quantum computation.

Place: Faculty of Mathematics, Physics and Computer Science, Wita Stwosza 59, Gdansk, room no. 361 (IFTiA).

January 30, 2020 at 12:15

Seminar given by Piotr Kwiek [in Polish]
University of Gdańsk
Title: Interferometr Macha-Zehndera z akustooptycznym dzielnikiem światła
The lecture is organised as a part of Division of Atomic Physics seminar. Future talks will be given in English.

Abstract:
W roku 1984 Leroy i Blomme opracowali podstawy teoretyczne dyfrakcji dwóch spójnych wiązek światła na fali ultradźwiękowej padających na nią pod dodatnim i ujemnym kątem Bragga. W roku 2019 teoria Leroya i Blommego została potwierdzona eksperymentalnie. Dokonano tego korzystając z interferometru Macha-Zehndera, w którym zwierciadło wyjściowe interferometru zastąpiono falą ultradźwiękową. Otrzymano zgodnie z teorią Leroya-Blomego zdudnianie wychodzącego światła z interferometru z częstością fali ultradźwiękowej. Następnie zamiast wiązek światła wprowadzono do interferometru skorelowane pary fotonów. Na wyjściu z interferometru otrzymano dwufotonowe zdudnianie par fotonów z częstością równą podwójnej częstości fali ultradźwiękowej. W referacie zostaną przedstawione podstawy teoretyczne oraz otrzymane wyniki eksperymentalne teorii Leroya-Blomego oraz jedno i dwufotonowego zdudniania odpowiednio fotonów i par fotonów.

Place: Faculty of Mathematics, Physics and Computer Science, Wita Stwosza 59, Gdansk, room no. 3.

January 23, 2020 at 14:15

Seminar given by Karol Życzkowski
Jagiellonian University, Cracow/ Center for Theoretical Physics, Warsaw/ KCIK, UG, Gdańsk
Title: Multipartite entanglement: combinatorics, topology, and … astronomy

Abstract:
A brief introduction to entanglement of multipartite pure quantum states will be given. As the Bell states are known to be maximally entangled among all two-qubit quantum states, a natural question arises: What is the most entangled state for the quantum system consisting of N sub-systems with d levels each? The answer depends on the entanglement measure selected, but already for four-qubit system there is no state, which displays maximal entanglement with respect to all three possible splittings of the systems into two pairs of qubits.
To construct strongly entangled multipartite quantum states one can use various mathematical techniques involving combinatorial designs, topological methods related to knot theory or the Majorana (stellar) representation of permutation symmetric quantum states.
Absolutely maximally entangled (AME) states of 2n subsystems, being maximally entangled with respect to all possible symmetric splitting of the system, find their applications for information processing tasks. For instance, the standard |GHZ_4^3> state of four qutrits allows one to teleport a single qutrit between any two parties, while the ‘more entangled’ AME state of four qutrits enables us to teleport two qutrits from any selected pair of users to the remaining two parties.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), second floor, seminar room no. C313.

January 21, 2020 at 11:00

Seminar given by Robert Alicki [in Polish]
International Centre for Theory of Quantum Technologies, UG
Title: Na początku była praca
The lecture is organized as a part of a Biophysical seminar by the Gdańsk Branch of the Polish Biophysical Society.

Abstract:
Przedstawione będą argumenty sugerujące, że początek ewolucji biologicznej wymagał powstania prymitywnych silników chemicznych wytwarzających pracę w postaci mechanicznych oscylacji. Zasada działania takich silników byłaby podobna do funkcjonowania akumulatorów, baterii, a także ogniw paliwowych, fotowoltaicznych i termoelektrycznych. Zgodnie z rozwijaną przez autora i współpracowników teorią, wszystkie te urządzenia wykorzystują sprzężenie zwrotne prowadzące do autooscylacji elektrycznie naładowanej warstwy podwójnej.

Place: Faculty of Mathematics, Physics and Computer Science, Wita Stwosza 57, Gdansk, the hall of the Faculty Council (room no. 21).

January 15, 2020 at 11:15

Seminar given by Horacio M. Pastawski
Title: Emergent Behavior in Quantum Dynamics of many-body systems: Quantum Dynamical Phase Transitions and Intrinsic Irreversibility observed through NMR Loschmidt Echoes and OTOCs

Abstract:
In recent years, Solid State Nuclear Magnetic Resonance (NMR) has given us the chance to observe surprising dynamical emergent phenomena [1]. This is possible because this technique addresses spins in the thermodynamic limit. We have addressed two phenomena: A) the polarization a spin dimmer, may have a Rabi oscillation that becomes an overdamped polarization transfer when the interaction with a spin environment becomes enough strong as compared with the Rabi frequency [2]. B) A dipolar scaled dynamics [2], which is seen as an apparent spin-diffusion through the study of Out of Time Order Correlations (OTOCs) associated with collective polarization. However, when the Hamiltonian strength is weak respect to uncontrollable residual interactions, Loschmidt Echo experiments reveals that dynamical transition from a reversible dynamics to an irreversible one whose time constant is fixed by the Hamiltonian itself, not by the residual interactions. This intrinsic irreversibility, shows that one should be careful in applying the Schrödinger Equation to many-body systems in the thermodynamic limit.

[1] Attenuation of polarization echoes in NMR: A test for the emergence of Dynamical Irreversibility in Many-Body Quantum Systems. PR Levstein, G Usaj, HM Pastawski, J. Chem. Phys. 108, 2718-2724 (1998)|

[2] Environmentally induced quantum dynamical phase transition in the spin swapping operation, GA Álvarez, EP Danieli, PR Levstein, and HM Pastawski. J. Chem. Phys. 124, 1 (2006)

[3]Emergent perturbation independent decay of the Loschmidt echo in a many-body system, CM Sánchez, AK Chattah, KX Wei, L Buljubasich, P Cappellaro, and HM Pastawski, Phys. Rev. Lett. (2020-in press)/ arXiv 1902.06628

[4]Loschmidt echo in many-spin systems: a quest for intrinsic decoherence and emergent irreversibility, PR Zangara and HM Pastawski, Phys. Scr. 92 033001(2017)

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), second floor, seminar room no. F305.

December 18, 2019 at 11:15

Seminar given by Carlo Maria Scandolo
Title: The entanglement of a bipartite channel

Abstract:
The most general quantum object that can be shared between two distant parties is a bipartite quantum channel. While much effort over the last two decades has been devoted to the study of entanglement of bipartite states, very little is known about the entanglement of bipartite channels. In this work, for the first time we rigorously study the entanglement of bipartite channels. We follow a top-down approach, starting from general resource theories of processes, for which we present a new construction of a complete family of monotones, valid in all resource theories where the set of free superchannels is convex. In this setting, we define various general resource-theoretic protocols and resource monotones, which are then applied to the case of entanglement of bipartite channels. We focus in particular on the resource theory of NPT entanglement. Our definition of PPT superchannels allows us to express all resource protocols and monotones in terms of semi-definite programs. Along the way, we generalize the negativity measure to bipartite channels, and show that another monotone, the max-logarithmic negativity, has an operational interpretation as the exact asymptotic entanglement cost of a bipartite channel. Finally, we show that it is not possible to distill entanglement out of bipartite PPT channels under any set of free superchannels that can be used in entanglement theory, leading us in particular to the discovery of bound entangled POVMs.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), second floor, seminar room no. F305.

QUANTUMSPEEDUP
2-5 December 2019, Leźno, Poland

The goal of the QUANTUMSPEEDUP conference is to gather experts and high-level practitioners in quantum physics and to exchange knowledge, ideas, experiences and expectations around the challenges of Quantum Technologies Flagship initiative.
Through a combination of keynote presentations given by renowned experts (IRAP leaders and senior researchers), speed talks and poster sessions the conference wants to open a debate among the IRAP units (ICTQT & QOT) and quantum scientific environment on possible cooperation in the context of the quantum technologies development.

We strongly encourage you and your teams to actively participate and prepare posters. In addition to a classical poster we kindly ask participants to prepare a short, three-minute presentation which she/he will present during a special Speed Talk session. Scheduled program attached

Conference venue: Pałac w Leźnie, Leźno 45, Gdańsk

December 6, 2019 at 13:15

Seminar given by Matteo Lostaglio
ICFO, Barcelona
Title: Contextual advantage for state-dependent cloning

Abstract:
A number of noncontextual models exist which reproduce different subsets of quantum theory and admit a no-cloning theorem. Therefore, if one chooses noncontextuality as one’s notion of classicality, no-cloning cannot be regarded as a nonclassical phenomenon. In this work, however, we show that there are aspects of the phenomenology of quantum state cloning which are indeed nonclassical according to this principle. Specifically, we focus on the task of state-dependent cloning and prove that the optimal cloning fidelity predicted by quantum theory cannot be explained by any noncontextual model. We derive a noise-robust noncontextuality inequality whose violation by quantum theory not only implies a quantum advantage for the task of state-dependent cloning relative to noncontextual models, but also provides an experimental witness of noncontextuality.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), second floor, seminar room no. F206.

November 29, 2019 at 12:15

Seminar given by Huihui Qin
Beijing Computational Science Research Center
Title: Quantifying Algebraic Asymmetry of Hamiltonian Systems

Abstract:
The symmetries play important roles in physical systems. We study the symmetries of a Hamiltonian system by investigating the asymmetry of the Hamiltonian with respect to certain algebras. We define the asymmetry of an operator with respect to an algebraic basis in terms of their commutators. Detailed analysis is given to the Lie algebra SU(2) and its q-deformation. The asymmetry of the q-deformed integrable spin chain models is calculated. The corresponding geometrical pictures with respect to such asymmetry is presented.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, lecture room no. 361.

November 6, 2019 at 11:15

Seminar given by Stella Seah
National University of Singapore
Title: Autonomous Quantum Thermal Machines

Abstract:
Autonomous thermal machines are useful as testbeds for understanding thermodynamics because they do not require external control and hence do not assume any hidden energy costs. In this talk, I will discuss some of the relevant topics in the field of quantum thermodynamics including (i) work definition in autonomous systems, (ii) description of open system dynamics for composite systems and (iii) measurement and its role in thermodynamics. Through simple models of autonomous machines, I will illuminate subtleties in terms of treatment of master equations and interpretation of energy exchanges in work extraction and measurement processes.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), third floor, seminar room no. F305

October 28, 2019 at 12:15

Seminar given by Sreetama Das
Harish-Chandra Research Instutute, India
Title: Quantum Information Processing in Noisy Environments

Abstract:
I will discuss various quantum informatic aspects when a system is interacting with an environment and the effects of disorder on the system induced by the environment. We study the ground state of a Hubbard model, which in the limit of large onsite interactions, is governed by the t-J Hamiltonian. We see that, in presence of doping, the entanglement is immutable under perturbative or sudden changes of system parameters, a phenomenon termed as adiabatic freezing. Significantly, at low fixed electron densities, the multipartite entanglement remains frozen across all parameter space. We also consider a quantum random walk, where we introduce a disorder in the number of steps a particle can take after each coin toss. These number of steps are independent and randomly chosen from Poisson distribution. We find that the spread of the walker is significantly inhibited, whereby it resides in the near-origin region, with respect to the case when there is no disorder. The scaling exponent of the quenched-averaged dispersion of the walker is sub-ballistic but super-diffusive. We also show that the features are universal to a class of sub- and super-Poissonian distributed quenched randomized jumps. If time permits, I will also discuss our work which derives an entanglement-based bound on non-Markovian behaviour of dynamics of a quantum system and necessarily transient cooling in quantum refrigerators.

References: 1. Adiabatic freezing of entanglement with insertion of defects in one-dimensional Hubbard model, arXiv:1708.07005. 2. Inhibition of spreading in quantum random walks due to quenched Poisson-distributed disorder, arXiv:1806.04024. 3. Almost Markovian maps and entanglement-based bound on corresponding non-Markovianity, arXiv:1905.06198. 4. Necessarily transient quantum refrigerator, arXiv:1606.06985.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

October 25, 2019 at 11:15

Seminar given by Andreas Hartmann
Institute for Theoretical Physics, University of Innsbruck, Austria
Title: Shortcuts to adiabaticity in many-body quantum heat engines

Abstract:
Quantum thermodynamics concerns the realisation thermodynamic cycles in quantum many-body systems. Due to the requirement of adiabaticity, a major challenge is to yield a non-vanishing power output or cooling power at finte times, respectively. One possibility available for coherent quantum strokes is to implement shortcuts to adiabaticity (STAs) to speed-up such, otherwise infinitely-long, cycles. Here we investigate the applicability of local approximate counter-diabatic protocols on many-body quantum heat engines (QHEs) where the working medium of our QHE is a many-body spin system. The counter-diabatically driven Otto cycle in this work shows a considerable increase in efficiency and power output compared to the adiabatic Otto cycle.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

October 23, 2019 at 11:15

Seminar given by Markus Grassl
Title: Symmetries of Weyl-Heisenberg SIC-POVMs

Abstract:
SIC-POVMs are generalised quantum measurements which are of particular interest in the context of quantum state tomography and quantum key distribution. Alternatively, they can be described by d^2
normalised vectors in the d-dimensional complex vector space such that the inner product between any pair of vectors has constant modulus. It has been conjectured that SIC-POVMs exist for all dimensions and that they can be constructed as orbits of a so-called fiducial vector under the Weyl-Heisenberg group. Despite a lot of effort, exact fiducial vectors are known for only a few dimensions, and numerical ones up to around dimension 150, together with some solutions in larger dimensions. Recently, exact and numerical solutions in record-dimensions 323 and 844, respectively, have been found as part of conjectured families obeying additional symmetries.
The talk will present the symmetries for this putative family together with generalisations. Links to number-theoretic conjectures in this context will be presented as well. This allows to convert numerical solutions of moderate precision into exact solutions, including dimension 844 mentioned above as well as the new record dimension 1299.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), third floor, seminar room no. F305

October 21, 2019 at 12:15

Seminar given by Arieh Ben-Naim
The Hebrew University of Jerusalem, Israel
Title: Entropy and the Second Law based on Information Theory

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

October 18, 2019 at 12:15

University of Kurdistan Hewler (UKH), Irak
Title: Quantum thermodynamic force and flow

Abstract:
Why do quantum evolutions occur and why do they stop at certain points? In classical thermodynamics, affinity was introduced to predict in which direction an irreversible process proceeds. In this paper, the quantum mechanical counterpart of the classical affinity is found. It is shown that the quantum version of affinity can predict in which direction a process evolves. A new version of the second law of thermodynamics is derived through quantum affinity for energy-incoherent state interconversion under thermal operations. we will also see that the quantum affinity can be a good candidate to be responsible, as a force, for driving the flow and backflow of information in Markovian and non-Markovian evolutions. Finally, we show that the rate of quantum coherence can be interpreted as the pure quantum mechanical contribution of the total thermodynamic force and flow. Thus it is seen that, from a thermodynamic point of view, any interaction from the outside with the system or any measurement on the system may be represented by a quantum affinity.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

October 11, 2019 at 12:15

Seminar given by Anubhav Chaturvedi
National Quantum Information Centre (KCIK), University of Gdansk
Title: Unifying quantum theory’s ontological (hidden variable) incompatibility

Abstract:
The ontological (hidden variable) framework provides for a vital ground for notions of classicality such as Bell’s local causality, Kochen-Specker’s non-contextuality, and Spekken’s non-contextuality. These notions of classicality formulated as principles, yield operational consequences that contradict predictions of quantum theory, thereby systematically discarding substantial classes of ontological models of quantum theory. Crucially, these notions highlight the different ways in which quantum theory departs from classical theories.
In this seminar, I shall facilitate a unifying insight into these seemingly distinct, yet related notions of classicality. Subsequently, I will present a new notion of classicality as the (hopefully natural) next piece in the puzzle. We refer to this notion as “bounded ontological distinctness”, quantum violation of which implies “quantum preparations, measurements, and transformations are more distinct than they are distinguishable”. This notion not only addresses many of the shortcomings of the other well-known notions of classicality but also unifies them such that violations of the other notions imply the violation of bounded ontological distinctness.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

October 3, 2019 at 11:30 a.m.

Seminar given by Tim Evans
University of Sydney
Title: Scalable Bayesian learning of local Hamiltonians and Lindbladians

Abstract:
As the size of quantum devices continues to grow, the development of scalable methods to characterise and diagnose noisy devices is becoming an increasingly important problem. Recent results demonstrate how a local Hamiltonians and Lindbladians can be reconstructed from a single, arbitrary steady state with a number of measurements that scales efficiently in the size of the system. These methods, however, can only characterise the system up to scalar factor and lack sufficient robustness to noise, both of which are imperative to be of practical use. In this talk I will present a Bayesian method that addresses both of these issues by making use of any, or all, of the following: experimental control of Hamiltonian couplings, the preparation of multiple states and the availability of any prior information we may already have for the Hamiltonian couplings. Moreover we provide an adaptive measurement protocol that can be performed online, updating estimates and their corresponding uncertainties as experimental data becomes available.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

September 30, 2019 at 11:30 a.m.

Seminar given by Marc-Olivier Renou
University of Geneva, Switzerland
Title: Triangle network nonlocality

Abstract:
Network nonlocality extends standard Bell nonlocality to networks, where several independent sources are distributed to several parties according to the network structure. Here we focus one the triangle network. The existence of a genuine quantum violation of triangle network
locality was open last years.
• We present the first genuine example of quantum nonlocality without inputs in the triangle scenario, a new form of quantum nonlocality [1].
• We generalize the Finner concentration inequality to quantum resources and Box World [2].
[1] MO. Renou, E. Bäumer, S. Boreiri, N. Brunner, N. Gisin, and S. Beigi, Phys. Rev. Lett., arXiv 1905.04902 (2019)
[2] MO. Renou, Y. Wang, S. Boreiri, S. Beigi, N. Gisin, and Nicolas Brunner, Phys. Rev. Lett. 123, 070403 (2019)

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

5th International Conference for Young Quantum Information Scientists (YQIS)
25-27 September 2019, Sopot, Poland

The aim of the conference series is to bring together early-stage researchers from a broad range of quantum information sciences. Apart from the oral and poster presentations of the participants and the invited speakers, the conference provides the opportunity for scientific and informal discussions in a relaxed environment.
YQIS organisers are the University of Gdansk and the National Quantum Information Centre (KCIK).

September 18, 2019 at 11:30 a.m.

Seminar given by Stanisław Szarek
Case Western Reserve University & Sorbonne University
Title: When Alice and Bob met Banach

Abstract:
As has been known for many decades, there are very close links between various flavors of functional analysis and quantum theory. We will report on one connection that became apparent in the last 10-15 years, namely on the interaction between the so-called Asymptotic Geometric Analysis and Quantum Information Theory. The former area investigates approximate symmetries and quantitative properties of high dimensional objects and includes, in particular, local theory of Banach spaces, convex geometry, and random matrices. The latter area constitutes a theoretical basis for the emerging quantum information technologies and for the quest to build a quantum computer. One of the reasons for this connection is the fact that quantum systems consisting of just several particles naturally lead to models whose dimension is from thousands to billions. We will introduce several invariants used to quantify the size or complexity of high-dimensional objects. We then indicate how these notions can be used to study entanglement and other phenomena that are of interest in quantum theory.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

September 3, 2019 at 11:30 a.m.

Seminar given by Erik Aurell
KTH-Royal Institute of Technology, Stockholm, Sweden
Title: Open quantum systems interacting with harmonic and anharmonic baths

Abstract:
The Feynman-Vernon approach to open quantum systems is to express the evolution of the reduced density matrix of the system as a double path integral, where one path (“forward path”) comes from the unitary U acting from the left, and one path (“backward path”) comes from the inverse unitary U^{\dagger} acting from the right. In the open systems context the Feynman-Vernon approach is closely related to the Keldysh theory, where the forward-backward paths correspond to the positive/negative parts of the Keldysh contour.
I will first present an alternative derivation of Feynman-Vernon theory by analyzing the von-Neumann-Liouville equation as a linear evolution law in the space of Hermitian operators. Results on full counting statistics (generating functions of energy changes in one or several baths), that are somewhat complicated to obtain in the path integral language, then emerge in a much simpler way.
I will then look at systems interacting linearly with baths that are not harmonic, but instead characterized by an expansion in cumulants. Every non-zero cumulant of certain environment correlation functions then gives a kernel in a higher-order term in the Feynman-Vernon action, and I will discuss a few of these higher-order terms.

This talks is partly work in progress; results so far are presented in joint paper with Ryoichi Kawai and Ketan Goyal, available as arXiv:1907.02671.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

August 2, 2019 at 11:30 a.m.

Seminar given by Jeongho Bang
Korea Institute for Advanced Study, South Korea
Title: Much easing learning-with-errors (LWE) problem with small-sized quantum samples

Abstract:
Learning-with-errors (LWE) problem has been a long-standing challenge in computation science and machine learning. In particular, the LWE problem offers many useful primitives in modern post-quantum cryptography, since it is believed as an “intractable” problem even in quantum setting. Meanwhile, very recently, Grilo et al. have proposed an efficient—i.e., exhibiting polynomial sample and running-time complexities—LWE algorithm which utilizes quantum samples and quantum Fourier transform (QFT). Nevertheless, we still have reservations about whether the Grilo et al’s algorithm truly beats the hardness of the LWE problem. The most serious issue is that a large number of data are required to be accessed in superposition during the sampling process. In general, however, such a task costs a lot of computational resources and even may offset the quantum efficiency. To circumvent this, here we propose a super-efficient and near-term implementable LWE algorithm with small-sized’ quantum samples.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

August 1, 2019 at 11:30 a.m.

Seminar given by Kabgyun Jeong
Seoul National University, South Korea
Title: Quantum channel capacity bounds through QEPI for bosonic Gaussian-noise channels

Abstract:
In this talk, I briefly review the entropy power inequality (EPI) from classical to quantum cases.
By using the EPI, I will introduce a method to bound quantum channel capacities on bosonc Gaussian channels.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

July 18, 2019 at 11:30 a.m.

Seminar given by Sergii Strelchuk
University of Cambridge, UK
Title: Hybrid quantum-classical computation and Clifford Magic circuits

Abstract:
Given the difficulty of building and controlling large numbers of qubits, early applications of quantum algorithms are likely to involve both quantum and classical ingredients. One of the most active areas of quantum computing investigates the fundamental limits of computation which could be carried out in these systems by studying the trade-off possibilities between classical and quantum resources. Inspired by a Pauli-based computing model by Bravyi et al. we will introduce a computational model of unitary Clifford circuits with solely magic state inputs (‘Clifford Magic’ circuits) supplemented by classical efficient computation, as well as an extended Gottesman-Knill theorem. I will further discuss the implications of achieving quantum advantage using Clifford Magic circuits and possible extensions to other gate sets. This talk is based on https://arxiv.org/abs/1806.03200.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

July 11, 2019 at 11:30 a.m.

Seminar given by Susane Calegari
Federal University of Santa Catarina, Brazil
Title: Genuine Multipartite Correlations in Dicke Superradiance

Abstract:
Correlations can describe global properties that are not explained by the sole knowledge of the features of the system parts. In this work, we study genuine multipartite correlations (GMC), correlations that cannot be reduced to lower partitions, in the Dicke model of superradiance. We compute GMC of order k for Dicke states with an arbitrary number of excitations and for the time-dependent superradiant state. The results display nonintuitive behaviours, i.e., there are situations in which genuine correlations between k particles are stronger than between m particles for k>m. Another feature is that the subsystems are more correlated right after the time of maximum emission of radiation. Finally, we use the weaving to classify how multipartite correlations scale by increasing the number of particles in the system and we observe that for larger N the GMC scale faster than the most correlated Dicke state, which may indicate the presence of correlations different from entanglement, such as quantum discord and classical correlations.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16

X Jubilee Symposium KCIK I Symposium ICTQT-KCIK
QUANTUM RESOURCES AND THEIR APPLICATION
23-25 May 2019, Sopot, Poland

The Symposium is jointly organized by National Quantum Information Centre (KCIK) and the International Centre for Theory of Quantum Technologies (ICTQT), University of Gdansk. Details are available on the web page: https://symposium-ictqt-kcik-2019-quantum-resources.ug.edu.pl/

Place: Quantum Information Center (KCIK) of the University of Gdansk, Gen. Wł. Andersa 27, 81-824 Sopot, lecture room

May 7, 2019 at 11 a.m.

Seminar given by Sebastian Szybka
Astronomical Observatory of the Jagiellonian University, Poland
Title: Standing gravitational waves in general relativity

Abstract:
We propose a covariant definition of standing gravitational waves in general relativity.

Place: Quantum Information Center (KCIK) of the University of Gdansk, Gen. Wł. Andersa 27, 81-824 Sopot, lecture room

April 10, 2019 at 4 p.m.

Seminar given by Łukasz Rudnicki
Max Planck Institute for the Science of Light, Germany
Title: Quantum correlations and complementarity of vectorial light fields

Abstract:
We explore quantum correlations of general vector-light fields in multislit interference, connecting the nth-order field correlations with the reduced n-photon states. The connection is utilized to examine photon wave-particle duality in the double-slit configuration, revealing that there is a hidden information-theoretic contribution that complements the standard inequality associated with such duality by transforming it into strict equality, a triality identity. We also establish a general quantum complementarity relation among the field correlations and the particle correlations which holds for any number of slits, correlation orders, and vector-light states. The framework that we advance hence uncovers fundamental physics about quantum interference.

Place: Faculty of Mathematics, Physics and Informatics UG, seminar room no. 361

February 26, 2019 at 11:30 a.m.

Seminar given by Peter Wittek
Perimeter Institute for Theoretical Physics, Canada
Title: Quantum-Enhanced Machine Learning: A Sanity Check

Abstract:
Machine learning is one of the fields that could benefit from near-term quantum computers: just the same way massively parallel digital computers enabled deep learning to scale up, quantum processing units (QPUs) are great at doing certain workloads. The problem is that the emergent field of quantum machine learning has been plagued with expectations that are unrealistic on contemporary quantum computers and relevance to the machine learning and AI communities have largely been overlooked. In this talk, we give a survey on what early quantum devices can contribute to machine learning. The primary algorithmic primitives are sampling, optimization, calculating kernel functions, and some variational problems efficiently which map to hybrid classical-quantum protocols. The main application areas in machine learning are probabilistic graphical models, in particular, Boltzmann machines and deep variants thereof, quantum neural networks, and searches over discrete parameter spaces. These models have different strengths than the ones trained on digital computers, hence quantum machine learning plays a complementary role to classical techniques, rather than acting as a replacement. We will also highlight possible pathways forward that would make upcoming quantum architectures more relevant to AI research.

Place: Faculty of Mathematics, Physics and Informatics UG, seminar room no. 361

February 6, 2019 at 12:15

Seminar given by Piotr Biskupski
IBM Polska Sp. z o.o., Poland
Title: The future is quantum – IBM Q experience

Abstract:
The rate of progress has been remarkable. Only a two years ago, we put the IBM Q experience prototype 5-qubit machine in the cloud, and made it available for the world to use, explore, and learn from. A year later, we added a second device with 50 qubits. Today, more than 100,000 users from more than 2000 universities, 600 high schools, and 400 private institutions have registered for accounts on the IBM Q experience, and collectively run 2 million experiments. The members of the research community have also published more than 170 research papers using our platform as a testbed for ideas. This is only the beginning.

Place: Faculty of Mathematics, Physics and Informatics UG, seminar room no. 361

December 18, 2018 at 1:00 p.m.

Seminar given by Aleksander Kubica
Perimeter Institute for Theoretical Physics, Canada
Title: Cellular-automaton decoders with provable thresholds for topological codes

Abstract:
I will propose a new cellular automaton, the Sweep Rule, which generalizes Toom’s rule to any locally Euclidean lattice. The Sweep Rule can be used to design a local decoder for the toric code in d≥3 dimensions, the Sweep Decoder, and to rigorously establish a lower bound on its performance. I will present numerical estimates of the Sweep Decoder threshold for the three-dimensional toric code on the cubic and body-centered cubic lattices for phenomenological phase-flip noise. Our results lead to new cellular-automaton decoders with provable error-correction thresholds for other topological quantum codes including the color code. If time permits, I will discuss recent progress in color code decoding in d≥2 dimensions. Based on joint work with J. Preskill, http://arXiv:1809.10145.

Place: Faculty of Mathematics, Physics and Informatics UG, seminar room no. 361

ICTQT Kick-Off Meeting
16 November 2018, Gdansk, Poland

We invite you cordially to participate in the opening ceremony of the International Centre for Theory of Quantum Technologies (ICTQT), which is a new joint research unit of the University of Gdansk and the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences.
The first part of this event will be of an official nature and during it will be presented the research program of the Centre and possible directions of cooperation with other scientific institutions. The second part of the event will take a form of a mini scientific symposium, with talks by invited speakers. Programme-ICTQT.
This is an extremely important day for ICTQT, but it is also a natural opportunity for quantum science community in Poland to meet and exchange opinions about possible cooperation within the field.

Place: Faculty of Social Sciences, Jana Bazynskiego 4, Gdansk

November 14, 2018 at 5.30 p.m.

Seminar given by Gerhard Leuchs
Max Planck Institute for the Science of Light (Erlangen), Germany
Title: The quantum vacuum – from an optics point of view

Place: Quantum Information Center (KCIK) of the University of Gdansk, Gen. Wł. Andersa 27, 81-824 Sopot, lecture room

November 14, 2018 at 4 p.m.

Seminar given by Bob Coecke
Oxford University, UK
Title: Quantum compilation and natural language processing in one picture

Abstract:
For well over a decade, we developed an entirely pictorial (and of course, formally rigorous) presentation of quantum theory [1], and it was recently shown that graphical reasoning can reproduce all equational reasoning in Hilbert space [2a, 2b]. In practical terms, it is currently for example being used as the core of quantum compilation [3], as it allows for easy translation between different computational models, allows for automation, and has outperformed any other method for circuit reduction. At present, experiments are also being setup aimed at establishing the age at which children could effectively learn quantum theory in this manner. Meanwhile, the pictorial language has also been successful in the study of natural language [4] which induces new quantum algorithms [5], and we have started to apply it to model cognition, where we employ GPT-alike models [6]. We present the key ingredients of the pictorial language as well as their interpretation across disciplines, and the applications mentioned above.

References:
[1] BC & A. Kissinger (2017) Picturing Quantum Processes. A first course on quantum theory and diagrammatic reasoning. Cambridge University Press.
[2a] E. Jeandel, S. Perdrix & R. Vilmart (2017) A Complete Axiomatisation of the ZX-Calculus for Clifford+T Quantum Mechanics. arXiv:1705.11151
[2b] K. F. Ng & Q. Wang (2017) A universal completion of the ZX-calculus. arXiv:1706.09877
[3] https://cambridgequantum.com/2017/10/20/collaboration-with-university-of-oxford-computer-science-department/

Place: Quantum Information Center (KCIK) of the University of Gdansk, Gen. Wł. Andersa 27, 81-824 Sopot, lecture room