Online Seminars on Quantum Information in Poland. Warsaw time zone.

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Past events

General guarantees for randomized benchmarking with random quantum circuits

Date: Wednesday, December 14, 2022
Time: 14:30
Host: Quantum Information and Quantum Computing Working Group
Passcode: nisq

Speaker: Ingo Roth (Quantum research centre, Technology Innovation Institute, Abu Dhabi, UAE)

Abstract Randomized benchmarking protocols have become the prominent tool for assessing the quality of gates on digital quantum computing platforms. In `classical’ variants of randomized benchmarking multi-qubit gates are drawn uniformly from a finite group. The functioning of such schemes can be rigorous guaranteed under realistic assumptions. In contrast, experimentally attractive and practically more scalable randomized benchmarking schemes often directly perform random circuits or use other non-uniform probability measures. An important example for such a non-uniform protocol is linear cross-entropy benchmarking. The theoretical understanding of non-uniform randomized benchmarking is still an ongoing effort. We present a new extension of general theoretical guarantees for randomized benchmarking to non-uniform measures. Combined with results on random walks, our results identify experimental parameter regimes where one can guarantee non-uniform randomized benchmarking protocols to work reliably. On the technical side, we develop a general perturbative description of noise in random circuits in terms of harmonic analysis that can also be used to analyze the noise-robustness of random circuit protocols beyond RB.

Quantum correlations from the post-quantum perspective: When can we have security against a super-quantum adversary ?

Date: Monday, December 5, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Passcode: please contact albertrico23 at gmail.com

Speaker: Paweł Horodecki (Gdansk)

Roman Ingarden Memorial Session 2022

Date: Wednesday, November 30, 2022
Time: 15:30
Host: KCIK
Passcode: 9yBJ7L

Details

Programme
15.30 – 15:55 Andrzej Jamiołkowski “My memories of Roman Stanisław Ingarden”.

16:00 – 16:55 2022 Ingarden Memorial Lecture

                        Peter Shor: “The development of quantum error correcting codes”

17:00 – 17:15 coffee break

17:15-17:45 Awarding of Junior KCIK Award for best Bachelor Thesis in quantum Information, talk of the winner

17:45-18:15 Distinguished talk

18:18 The End

Hybrid Quantum-Classical Codes

Date: Wednesday, November 30, 2022
Time: 12:30
Host: ICTQT, room 317
Passcode: 3SM3fW

Speaker: Andrew Nemec (Duke University)

Abstract Hybrid codes simultaneously encode both quantum and classical information together, giving an advantage over coding schemes where the quantum and classical information are transmitted separately. We construct the first known families of hybrid codes that are guaranteed to provide an advantage over quantum codes, as well as also giving a construction of hybrid codes from subsystem codes that allow for different minimum distances for the encoded quantum and classical information . We also show how hybrid codes can be applied to the problem of faulty syndrome measurements and lead to the construction of new quantum data-syndrome codes.

Hybrid Quantum-Classical Codes

Date: Monday, November 28, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University), Meeting id: 896 0129 1160
Passcode: please contact albertrico23 at gmail.com

Speaker: Andrew Nemec (Duke University, USA)

Abstract Hybrid codes simultaneously encode both quantum and classical information together, giving an advantage over coding schemes where the quantum and classical information are transmitted separately. We construct the first known families of hybrid codes that are guaranteed to provide an advantage over quantum codes, as well as also giving a construction of hybrid codes from subsystem codes that allow for different minimum distances for the encoded quantum and classical information . We also show how hybrid codes can be applied to the problem of faulty syndrome measurements and lead to the construction of new quantum data-syndrome codes.

Graph Approach to Entanglement Generation in Linear Quantum Networks

Date: Wednesday, November 23, 2022
Time: 14:00
Host: ICTQT, room 317
Passcode: 743020

Speaker: Seungbeom Chin (ICTQT / Sungkyunkwan University)

Abstract We propose a graph method to systematically search for schemes that obtains genuine entanglement in arbitrary N-partite linear quantum networks (LQNs). While the indistinguishability of quantum particles is widely used as a resource for the generation of entanglement, it is challenging to devise a suitable LQN that carries a specific entangled state. Our research presents a mapping process of arbitrary LQNs to graphs, which provides an organized strategy for designing LQNs to generate multipartite entanglement with and without postselection. This talk is based on Quantum 5 (2021), 611 and arXiv:2211.04042.

All quantum spectra in one shot

Date: Wednesday, November 23, 2022
Time: 12:30
Host: ICTQT, room 317
Passcode: 743020

Speaker: Carlos L. Benavides-Riveros (MPI for the Physics of Complex Systems, Dresden / University of Trento)

Abstract Determining the properties of the excitations in quantum many-body systems is a fundamental problem across almost all sciences. For instance, quantum excited states underpin new states of matter, support biological processes such as vision, or determine optoelectronic properties of photovoltaic devices. Yet, while ground-state properties can be determined by rather accurate computational methods, there remains a need for theoretical and computational developments to target excited states efficiently. Inspired by the duplication of the Hilbert space used to study black-hole entanglement and the electronic pairing of conventional superconductivity, we have recently developed a new variational scheme to compute the full spectrum of a quantum many-body Hamiltonian, rather than only its ground or the lowest-excited states. An important feature of our proposed scheme is that these spectra can be computed in a one-shot calculation. The scheme thus provides a novel variational platform for excited-state physics. In the talk, I will show an explicit calculation for a Fermi-Hubbard Hamiltonian, based on a unitary coupled-cluster ansatz. Since our approach is suitable for efficient implementation on quantum computers, we believe this “variational quantum diagonalizer” has the potential to enable unprecedented calculations of excited-state processes of quantum many-body systems.
The talk is based on C. L. Benavides-Riveros et al., Phys. Rev. Lett. 129, 066401 (2022)

Mutually unbiased measurements

Date: Wednesday, November 23, 2022
Time: 12:30
Host: Center for Theoretical Physics Colloquium
Passcode: 134595

Speaker: Máté Farkas (ICFO, Barcelona)

Abstract Mutually unbiased bases (MUBs) correspond to measurements in quantum theory that are complementary: if a measurement in a basis yields a definite outcome on a given quantum state, then a measurement in a basis unbiased to the first one yields a uniformly random outcome on the same state. Simple examples of MUBs are photon polarisation measurements in the horizontal and vertical directions, or spin measurements in the z and x directions of a spin-1/2 particle. Their complementary property makes MUBs highly useful in various quantum information processing tasks, such as quantum state tomography, communication tasks, Bell inequalities, and quantum cryptography.

In this talk—after an introduction to MUBs and their use in quantum information—I will introduce a generalisation of MUBs termed mutually unbiased measurements (MUMs). MUMs retain the complementary property of MUBs in a “device-independent” manner: in order to define MUMs, one does not need to refer to the Hilbert space dimension (the number of degrees of freedom, which is not an observable property), only to the outcome number of the measurements (an operational property). I will discuss the mathematical characterisation and constructions of MUMs, and the fundamental similarities and differences between MUBs and MUMs. Then, I will introduce a family of Bell inequalities tailored to MUMs, and show how to use these inequalities for device-independent quantum cryptography, as well as how to use these Bell inequalities to tackle a long-standing open problem on the number of MUBs in a given Hilbert space dimension.

Certification of unknown quantum measurements

Date: Monday, November 21, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University), Meeting id: 896 0129 1160
Passcode: please contact albertrico23 at gmail.com

Speaker: Zbigniew Puchala (IITiS Gliwice)

Quantum Error Correction with Superconducting Transmon Qubits

Date: Wednesday, November 16, 2022
Time: 15:30
Host: Team-Net Quantum Computing Colloquium
Passcode: teamnet

Speaker: Barbara Terhal (QuTech, TU Delft & Forschungszentrum Juelich)

Abstract We review the goals of quantum error correction, in particular the use of the surface code. We discuss some of the results and challenges in experimental quantum error correction, in particular with respect to qubit leakage.