Tu znajdziesz listę organizowanych w Polsce spotkań, seminariów i konferencji związanych z zagadnieniami informacji kwantowej

Squeezing and ultrastrong coupling of light and matter

Date: czwartek, 3 listopada, 2022
Time: 11:00
Host: ICTQT Seminar, room D 102, Chemistry Department, UG
Zoom link: https://zoom.us/j/7763535903?pwd=Q1VwQWhHME9GcjBJaUhEZWoxazhDdz09
Passcode: 743020

Speaker: Adam Miranowicz, Adam Mickiewicz University (Poznań) and RIKEN (Wako)

Abstract Experimental demonstrations and control of strong coupling of light and matter has lead to various applications for lasers, quantum sensing, and quantum information processing since 1980s. In my talk, I will review [1] recent theoretical and experimental progress in the ultrastrong coupling (USC) and deep-strong coupling (DSC) regimes of light and matter, which are characterized by the coupling strengths comparable to their transition frequencies. In the last few years, the USC regime has been experimentally achieved in a wide range of different systems with very different spectral ranges. These systems include: superconducting quantum circuits, intersubband polaritons, Landau polaritons, organic molecules, magnetic systems, nano-plasmonics, and optomechanical systems. Emerging applications of the USC and DSC regimes are focused on quantum technologies and quantum information processing.

The ground state of light-matter systems in the DSC regime is a Schroedinger-cat state, where virtual photons are entangled with virtual excitations of the matter. A recent experimental demonstration of the cat state can be considered as the discovery of a new stable molecular state in which light and matter are hybridized [2]. The USC and DSC regimes can be effectively reached by squeezing a cavity field as proposed in [3] and experimentally demonstrated in [4]. This type of light squeezing can also be used to increase spin squeezing [5], which is of paramount importance for quantum metrology. The USC and DSC regimes enable also generating giant Schrodinger cat states of real photons and atomic real excitations by applying squeezing [6,7]. The USC methods have inspired developing a promising technique to beat the 3 dB limit for intracavity squeezing and, thus, to effectively apply it for nondemolition qubit experiments [8].

Co-authors: Franco Nori, Wei Qin, Ye-Hong Chen, Anton Kockum, Simone De Liberato, Salvatore Savasta

[1] A. F. Kockum, A. Miranowicz, S. De Liberato, S. Savasta, and F. Nori: Ultrastrong coupling between light and matter, Nat. Rev. Phys. 1, 19 (2019). [2] F. Yoshihara, T. Fuse, S. Ashhab, K. Kakuyanagi, S. Saito, and K. Semba, Superconducting qubit-oscillator circuit beyond the ultrastrong-coupling regime, Nat. Phys. 13, 44 (2017). [3] W. Qin, A. Miranowicz, P.-B. Li, X.-Y. Lu, J.-Q. You, and F. Nori: Exponentially Enhanced Light-Matter Interaction, Cooperativities, and Steady-State Entanglement Using Parametric Amplification, Phys. Rev. Lett. 120, 093601 (2018). [4] S. C. Burd, R. Srinivas, H. M. Knaack, W. Ge, A. C. Wilson, D. J. Wineland, D. Leibfried, J. J. Bollinger, D. T. C. Allcock, and D. H. Slichter, Quantum amplification of boson-mediated interactions, Nat. Phys. 17, 898 (2021). [5] W. Qin, Y.-H. Chen, X. Wang, A. Miranowicz, and F. Nori: Strong Spin Squeezing Induced by Weak Squeezing of Light inside a Cavity, Nanophotonics 9, 4853 (2020). [6] W. Qin, A. Miranowicz, H. Jing, and F. Nori: Generating long-lived macroscopically distinct superposition states in atomic ensembles, Phys. Rev. Lett. 127, 093602 (2021). [7] Y.-H. Chen, W. Qin, X. Wang, A. Miranowicz, F. Nori: Shortcuts to Adiabaticity for the Quantum Rabi Model: Efficient Generation of Giant Entangled Cat States via Parametric Amplification, Phys. Rev. Lett. 126, 023602 (2021). [8] W. Qin, A. Miranowicz, and F. Nori: Beating the 3 dB Limit for Intracavity Squeezing and Its Application to Nondemolition Qubit Readout, Phys. Rev. Lett. 129, 123602 (2022).

Reconstructing the whole from its parts

Date: poniedziałek, 31 października, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us02web.zoom.us/j/85911849629
Passcode: subspace

Speaker: Dardo Goyeneche (Universidad de Antofagasta, Chile)

Abstract The quantum marginal problem consists in deciding whether a given set of marginal reductions is compatible with the existence of a global quantum state or not. In this talk, we formulate the problem from the perspective of dynamical systems theory and study its advantages with respect to the standard approach. The introduced formalism allows us to analytically determine global quantum states from a wide class of self-consistent marginal reductions in any multipartite scenario. In particular, we show that any self-consistent set of multipartite marginal reductions is compatible with the existence of a global quantum state, after passing through a depolarizing channel. This result reveals that the complexity associated with the marginal problem can be drastically reduced when restricting the attention to sufficiently mixed marginals. We also formulate the marginal problem in a compressed way, in the sense that the total number of scalar constraints is smaller than the one required by the standard approach.

Reconstructing the whole from its parts

Date: środa, 26 października, 2022
Time: 14:00
Host: ICTQT
Zoom link: https://zoom.us/j/7763535903?pwd=Q1VwQWhHME9GcjBJaUhEZWoxazhDdz09
Passcode: 743020

Speaker: Dardo Goyeneche (Universidad de Antofagasta, Chile)

Abstract The quantum marginal problem consists in deciding whether a given set of marginal reductions is compatible with the existence of a global quantum state or not. In this talk, we formulate the problem from the perspective of dynamical systems theory and study its advantages with respect to the standard approach. The introduced formalism allows us to analytically determine global quantum states from a wide class of self-consistent marginal reductions in any multipartite scenario. In particular, we show that any self-consistent set of multipartite marginal reductions is compatible with the existence of a global quantum state, after passing through a depolarizing channel. This result reveals that the complexity associated with the marginal problem can be drastically reduced when restricting the attention to sufficiently mixed marginals. We also formulate the marginal problem in a compressed way, in the sense that the total number of scalar constraints is smaller than the one required by the standard approach.

Engineering and tomography of collective quantum state in gases

Date: poniedziałek, 24 października, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us02web.zoom.us/j/85911849629
Passcode: subspace

Speaker: Szymon Pustelny (Institute of Theoretical Physics, JU)

Abstract The ability to generate, modify, and retrieve a quantum state is of paramount importance for quantum information. Conventional physical implementations of the schemes, enabling realization of the tasks, employ single microscopic objects (atoms, photons, superconducting circuits, etc.). However, operation with such objects presents many experimental challenges. In the seminar, an alternative approach, enabling realization of quantum-state engineering and tomography using the collective state of many atoms (10^9), will be presented.

An optimal LCU-based quantum linear system solver

Date: środa, 12 października, 2022
Time: 16:00
Host: Team-Net Quantum Computing Colloquium
Zoom link: https://us06web.zoom.us/j/81247873600
Passcode: teamnet

Speaker: Sander Gribling (Université de Paris)

Abstract In this talk, I will first give an overview of recent techniques such as taking linear combinations of unitaries (LCU) and the quantum singular value transformation framework (QSVT). These techniques allow one to reduce many quantum algorithmic problems to questions about finding good / the best polynomial approximations to certain functions. We study one such function: the inverse. In other words, we consider the problem of solving linear systems of equations. Prior work has shown that an asymptotically optimal approximation to the inverse can be evaluated using LCU and/or QSVT. We show the same for the optimal approximating polynomial, thus achieving constant factor improvements.

This is based on https://arxiv.org/abs/2109.04248 which is joint work with Daniel Szilagyi and Iordanis Kerenidis.

About the speaker: Sander Gribling’s research focuses on the interaction between optimization and quantum information theory / quantum computing. He is also interested in the many uses of polynomials in quantum information theory: polynomial optimization, quantum query complexity, and quantum algorithms.

Certification of entangled quantum states and quantum measurements in Hilbert spaces of arbitrary dimension

Date: środa, 12 października, 2022
Time: 12:30
Host: Center for Theoretical Physics Colloquium
Zoom link: https://zoom.us/j/82380380442?pwd=Z3IyeEhlZmFHU1B2M2VUVVJhODkrUT09
Passcode: 134595

Speaker: Shubhayan Sarkar (CTP, PAS)

Abstract A lot of work has recently been put into finding device-independent certification schemes for composite quantum systems. Most of them are however restricted to lower-dimensional systems, in particular two-qubit states. In this talk, I will first explain the basics of device-independent certification of quantum systems. Then, I will present some of our recent results that certify entangled quantum states of arbitrary local dimension and large classes of arbitrary outcome quantum measurements. Finally, I will present a scheme to certify the optimal amount of randomness that can be generated from arbitrary dimensional quantum systems.

Your spectra don’t fit: a semidefinite programming hierarchy for the quantum marginal problem

Date: poniedziałek, 3 października, 2022
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us02web.zoom.us/j/85911849629
Passcode: subspace

Speaker: Felix Huber (Institute of Theoretical Physics, UJ)

Abstract

Asymptotics and typicality of sequential generalized measurements

Date: środa, 28 września, 2022
Time: 15:15
Host: Quantum Information and Quantum Computing Working Group (CTP PAS)
Zoom link: https://us06web.zoom.us/j/88571566818
Passcode: nisq

Speaker: Wen-Long Ma (Institute of Semiconductors, Chinese Academy of Sciences)

Abstract The relation between projective measurements and generalized quantum measurements is a fundamental problem in quantum physics, and clarifying this issue is also important to quantum technologies. While it has been intuitively known that projective measurements can be constructed from sequential generalized or weak measurements, there is still lack of a proof of this hypothesis in general cases. Here we rigorously prove it from the perspective of quantum channels. We show that projective measurements naturally arise from sequential generalized measurements in the asymptotic limit. Specifically, a selective projective measurement arises from a set of typical sequences of sequential generalized measurements. We provide an explicit scheme to construct projective measurements of a quantum system with sequential generalized quantum measurements. Remarkably, a single ancilla qubit is sufficient to mediate a sequential weak measurement for constructing arbitrary projective measurements of a generic system. As an example, we present a protocol to measure the modular excitation number of a bosonic mode with an ancilla qubit.

Distinguishability-induced many-body decoherence

Date: środa, 28 września, 2022
Time: 12:00
Host: ICTQT
Zoom link: https://zoom.us/j/7763535903?pwd=Q1VwQWhHME9GcjBJaUhEZWoxazhDdz09
Passcode: 743020

Speaker: Christoph Dittel (University of Freiburg)

Abstract Indistinguishability is the essential ingredient for many-body interference — a purely quantum mechanical interference effect between many identical bosonic or fermionic particles that can be exploited for a variety of applications, ranging from simulations with ultracold atoms to photonic quantum information processing. In this talk I give an introduction into this fascinating many-body property. Starting from its consequences on interference effects, I show how partial particle distinguishability entails a wave-particle duality relation on the many-body level. Moreover, I discuss how partial distinguishability due to mixedness — in the particles’ internal degrees of freedom — induces many-body decoherence whose strength increases exponentially in the number of constituents.

What is nonclassical about uncertainty relations?

Date: środa, 3 sierpnia, 2022
Time: 14:15
Zoom link: https://zoom.us/j/7763535903?pwd=Q1VwQWhHME9GcjBJaUhEZWoxazhDdz09
Passcode: 743020

Speaker: Lorenzo Catani (TU Berlin)

Abstract Uncertainty relations express limits on the extent to which the outcomes of distinct measurements on a single state can be made jointly predictable. The existence of nontrivial uncertainty relations in quantum theory is generally considered to be a way in which it entails a departure from the classical worldview. However, this view is undermined by the fact that there exist operational theories which exhibit nontrivial uncertainty relations but which are consistent with the classical worldview insofar as they admit of a generalized-noncontextual ontological model. This prompts the question of what aspects of uncertainty relations, if any, cannot be realized in this way and so constitute evidence of genuine nonclassicality. We here consider uncertainty relations describing the tradeoff between the predictability of a pair of binary-outcome measurements (e.g., measurements of Pauli X and Pauli Z observables in quantum theory). We show that, for a class of theories satisfying a particular symmetry property, the functional form of this predictability tradeoff is constrained by noncontextuality to be below a linear curve. Because qubit quantum theory has the relevant symmetry property, the fact that it has a quadratic tradeoff between these predictabilities is a violation of this noncontextual bound, and therefore constitutes an example of how the functional form of an uncertainty relation can witness contextuality. We also deduce the implications for a selected group of operational foils to quantum theory and consider the generalization to three measurements. Based on https://arxiv.org/abs/2207.11779.
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