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|21.01.2021||Chandan Datta||CENT, UW||Entanglement-assisted perfect discrimination of quantum measurements|
|28.01.2021||Anicet Tibau Vidal||University of Oxford||Fermions are local realistic|
|11.02.2021||Daniel McNulty||Aberystwyth University||Connections between measurement incompatibility and quantum coherence||https://tinyurl.com/youtube-ctp|
|18.02.2021||Marcin Markiewicz||ICTQT, University of Gdansk||On construction of t-designs for SL(2, C) via its Cartan decomposition|
|25.02.2021||Uttam Singh||CTP PAS||A no go theorem for local Gaussian work extraction for multimode bosonic systems|
|04.03.2021||David Wierichs||University of Cologne||Avoiding local minima in variational quantum eigensolvers with the natural gradient optimizer|
|11.03.2021||Karol Horodecki||ICTQT, University of Gdansk||Upper bounds on the rate in device-independent quantum key distribution|
|18.03.2021||Marco Túlio Quintino||University of Vienna|
Universal protocols for transforming unitary quantum operations:
Exponential advantage with adaptive protocols and the power of indefinite causality
|25.03.2021||Michael R. Geller||University of Georgia||Quantum Error Mitigation for SPAM|
|08.04.2020||Anna Szymusiak||Jagielonian University||Morphophoric quantum measurements, generalised qplexes, and 2-designs|
|15.04.2021||Dariusz Chruściński||UMK Toruń||On the universal constraints for relaxation rates for quantum dynamical semigroup|
|22.04.2021||Emanuele Marconato||Universita di Torino||The relation between the witness of non-classicality and hybrid systems|
|29.04.2021||Magda Stobinska||FUW||Efficient long-range distribution of multi-photon entanglement|
|06.05.2021||Ernesto Galvao||UFF & IINL||Measuring the projective-unitary invariant properties of a set of states, and applications|
|13.05.2021||Nikolai Miklin||ICTQT||Quantifying causal influences in the presence of a quantum common cause|
|20.05.2021||Daniel Reitzner||Slovac Academy of Sciences|
General Measurements with Limited Resources and Their Application to Quantum Unambiguous State Discrimination
|27.05.2021||Stasja Stanisic||PhaseCraft||Error mitigation by training with fermionic linear optics|
|10.06.2021||Cristina Cirstoiu||Cambridge Quantum Computing||Estimation of correlations and non-separability in quantum channels via unitarity benchmarking|
|17.06.2021||Adam Glos||IITiS||Infeasible space reduction for QAOA through encoding change|
In the era of Noisy Intermediate-Scale Quantum (NISQ) computing, the design of space-efficient and fault-tolerant quantum algorithms is inevitable. Considering the problems defined over permutations, it becomes harder to reach the optimal solutions as for some problems the feasible solutions constitute only a small fraction of the whole space. Addressing these issues, we propose Encoding-Changing Quantum Approximate Optimization Algorithm (EC-QAOA), which bases on a different ansatz compared to the original QAOA. We demonstrate the effectiveness of the proposed method through the Travelling Salesman Problem. Furthermore, we show that the proposed approach enables quantum error mitigation using mid-circuit measurements. We compare the performance of the proposed method with the existing approaches by numerical studies.
|24.06.2021||Grzegorsz Rajchel-Mieldzioć||CFT PAN||Classical to quantum transition using bistochastic matrices|
Bistochastic and unitary matrices are similar concepts in respectively classical and quantum domains. We investigate the connection between them, in particular the problem of determining which bistochastic matrix has its unitary counterpart, i.e. the unistochasticity problem, with applications ranging from quantum walks to particle physics. The talk shall be composed of an exposition of the results concerning new algebraical and geometrical structures inside bistochastic matrices.
|01.07.2021||Marek Gluza||Freie Universität Berlin||Fidelity witnesses|
Once a quantum computation or simulation setup gains in size and coherence new research challenges appear when trying to get a handle on what the experimental device is doing. One of the most immediate questions that emerges is simply: How can I know that the system performs correctly if quantum state tomography is out of reach? Broadly speaking, we would like to devise ways for certifying successful implementations of quantum protocols despite large numbers of degrees of freedom involved in the process. In the talk I will describe the notion of fidelity witnesses which offer an experimentally-friendly way for circumventing the difficulty of measuring the fidelity between a known target quantum state and an unknown experimental preparation. Part of the talk will be devoted to specific fidelity witnesses useful for certifying high-fidelity state preparations of fermionic Gaussian states which recently found an application on the Sycamore quantum processor. Besides giving an overview of what is the current understanding of the range of applicability of the fidelity witness approach to verifying quantum simulators, I will also hint at comparisons to other post-tomographic certification methods.
|08.07.2021||Michał Eckstein||Jagiellonian University||Quantum Optimal Transport|
The optimal transport problem, established by Monge and refined by Kantorovich and Wasserstein, has ubiquitous applications in statistics, machine learning, computer vision and early Universe reconstruction. Recently, several approaches towards its quantum version have been developed. In the talk I will provide an overview of the quantum optimal transport problem. The general results will be illustrated with a more detailed study of the single-qubit transport problem. In particular, I will show that the quantum optimal transport induces a new metric on the Bloch ball with intriguing properties. The talk is based on a joint work with S. Cole, S. Friedland and K. Życzkowski - arXiv:2102.07787, 2105.06922.
|23.09.2021||Aleksandra Krawiec||IITiS PAN||Discrimination of quantum measurements and channels|
My presentation will be focused on various approaches towards the task of discrimination of quantum measurements and channels. I will elaborate on minimum error discrimination, unambiguous discrimination, and asymmetric discrimination, which is also known as certification. All of these approaches will be considered in the single-shot scheme as well as multiple-shot scenarios. I will also discuss when parallel strategies are optimal for discrimination and when the use of additional processing in adaptive scheme gives an advantage over the parallel one.
|30.09.2021||Oskar Słowik||CFT PAN||Designing locally maximally entangled quantum states with arbitrary local symmetries|
One of the key ingredients of many LOCC protocols in quantum information is a multiparticle (locally) maximally entangled quantum state, aka a critical state, that possesses local symmetries. It is natural to ask if such states exist in a given quantum system and how do they look like. During my talk, I will briefly explain why such states are important. Then, I will introduce some relevant notions, such as diagonal H-symmetries, and move to the main technical result which states that the Nth tensor power of any irreducible representation of SU(N) contains a copy of the trivial representation. The rest of the talk will be devoted to the applications of the main result with its corollaries and examples of designing critical states with large local unitary symmetry. In particular, I will explain that critical states with large local symmetries can be realised in a quantum system of distinguishable traps with bosons or fermions occupying a finite number of modes. I will also link our results with the existence of so-called strictly semistable states with particular asymptotic diagonal symmetries.
|06.10.2021||Yink Loong Len||University of Warsaw||Quantum Metrology with Imperfect Measurements|
The impact of measurement imperfections on quantum metrology protocols has been largely ignored, even though these are inherent to any sensing platform in which the detection process exhibits noise that neither can be eradicated, nor translated onto the sensing stage and interpreted as decoherence. In this seminar, we report our recent work in addressing the issue of imperfect measurement in quantum metrology, in a systematic manner (arXiv:2109.01160). Specifically, we demonstrate how the quantum Fisher information must be modified to account for noisy detection, and we propose tractable methods allowing for its approximate evaluation. Using this general expression, we then prove a go-theorem, which states that in canonical scenarios involving N probes with local measurements undergoing readout noise, the effect of noisy detection can be counterbalanced, by implementing a suitable global control unitary operation before the readout stage. This shows that the ideal, quantum-enhanced sensitivity (e.g. Heisenberg scaling) can always be recovered given a large enough number of probes. On the contrary, we also prove a no-go theorem, which states that such a feat cannot however be achieved with just local control operations, where the optimal sensitivity will then be limited to just a constant factor improvement over the classical results, which scales linearly with the probe size. We illustrate our results with a relevant example of an NV-centre used to sense a magnetic field, as well as schemes involving spin-1/2 probes (qubits) with bit-flip errors affecting their two-outcome measurements. We also provide the input states and control unitary operations sufficient to attain the ultimate asymptotic precision.
|13.10.2021||Zuzana Gavorova||The Hebrew University of Jerusalem||Controlled-unitary is impossible in the quantum circuit model|
I will discuss the following task: given an unknown unitary gate U as a black box, implement the controlled-unitary* gate. Araújo et al. showed that a quantum circuit that makes one call to U cannot implement controlled-U. I will show that the task remains impossible even if the quantum circuit is allowed any number of calls to U. Our result also excludes circuits that use postselection and only approximate the task. Handling approximation and postselection simultaneously requires a new notion: diamond distance for the postselected setting. * Up to a certain relative phase. The papers: arXiv:2011.10031 arXiv:2011.08487
|20.10.2021||Adrián Solymos||Eötvös Loránd University, Budapest||Extendibility of quantum states|
Unlike classical states, quantum states cannot necessarily be extended in such a way that the two-particle reduced states are all identical. More precisely, only the separable states are those that can be extended in such a way. The so-called shareability or extendibility number describes to how many parties a given state can be extended to. This is a good entanglement measure (i.e., a LOCC-monotone function), however, it has been calculated only for a few types of states. The talk presents the (k,l)-shareable states for a set Werner-like states, and the set of (1,2)-shareable OO-states.
|27.10.2021||Shubhayan Sarkar||CFT PAN||Certification of quantum systems using quantum steering|
Device-independent certification schemes have gained a lot of interest lately. In this regard, we explore quantum steering for certifying higher-dimensional quantum systems in a one-sided device-independent way. In the first part of the talk, I would discuss our proposal of a one-sided device-independent protocol that could certify any set of d-outcome projective measurements which do not share any common invariant subspace which we termed as “genuinely incompatible measurements” which includes mutually unbiased bases which are an important resource for quantum cryptography. We also find the robustness of our protocol for a class of mutually unbiased bases towards experimental imperfections. In the second part of the talk, I would discuss our proposal of a one-sided device-independent protocol that could certify any bipartite entangled state using a minimal number of measurements possible, that is, two per subsystem. Using the certified state, we were able to certify every extremal POVM which in turn can be used to certify randomness of amount 2logd bits, which is the maximum amount that can be achieved using quantum systems of dimension d.
|17.11.2021||Laura Marcinska||QMATH, University of Copenhagen|
|24.11.2021||Daniel J. Brod||UFF Niteroi|
|01.12.2021||David Gross||University of Cologne|
|08.12.2021||Beata Zjawin||ICTQT Gdansk|
|15.12.2021||Omar Fawzi||ENS Lyon|