Joint Seminar on Quantum Information and Technologies
2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025 | YouTube channel
until 2023/2024 Quantum Information Seminar | YouTube channel
2021-06-17 (Thursday)
join us at 11:15 
David Arvidsson Shukur (University of Cambridge)Quantum Learnability is Arbitrarily Distillable
Zoom link: https://zoom.us/j/6526721604?pwd=Y0pPdE9vT1hNWWNiZVBMaEVOeHN2dz09
Quantum learning (in metrology and machine learning) involves estimating unknown parameters from measurements of quantum states. The quantum Fisher information matrix can bound the average amount of information learnt about the unknown parameters, per experimental trial. In several scenarios, it is advantageous to concentrate information in as few states as possible. In this talk, I will present a “go-go” theorem proving the possibility of unbounded and lossless distillation of Fisher information about multiple parameters in quantum learning. Our results enable the construction of filters that can reduce arbitrarily the quantum-state intensity on experimental detectors, whilst retaining all initial information. I will show that the quantum resource that enables this is negativity, a narrower nonclassicality concept than noncommutation.
Quantum learning (in metrology and machine learning) involves estimating unknown parameters from measurements of quantum states. The quantum Fisher information matrix can bound the average amount of information learnt about the unknown parameters, per experimental trial. In several scenarios, it is advantageous to concentrate information in as few states as possible. In this talk, I will present a “go-go” theorem proving the possibility of unbounded and lossless distillation of Fisher information about multiple parameters in quantum learning. Our results enable the construction of filters that can reduce arbitrarily the quantum-state intensity on experimental detectors, whilst retaining all initial information. I will show that the quantum resource that enables this is negativity, a narrower nonclassicality concept than noncommutation.
2021-06-10 (Thursday)
join us at 11:15
Katarzyna Macieszczak (University of Cambridge)Operational approach to metastability in open quantum systems
Zoom link: https://zoom.us/j/6526721604?pwd=Y0pPdE9vT1hNWWNiZVBMaEVOeHN2dz09
Metastability is a phenomenon of a large separation in dynamical timescales, leading to a prolonged temporal regime when system states appear stationary before eventually relaxing towards a true, usually unique, steady state. For classical equilibrium dynamics, metastability can be understood as a consequence of multiple local minima present in the system free energy function, but for non-equilibrium dynamics such a general description linking dynamic and static properties is elusive. In this talk, I will introduce an information-theoretic approach of quantifying how non-stationary an open quantum system is during a given time regime [1]. Despite its abstractness, this approach arises directly from experimental considerations of how the averages of observables change with time in a finitely dimensional system. For dynamics governed by a master equation, I will then draw upon a simple but powerful analogy with exponential decay, to investigate regimes when such changes are negligible according to the logarithmic scale of time, and thus the system can be viewed as approximately stationary. I will show that a distinct regime of approximate stationarity may arise beyond the initial and final regimes of the dynamics, which provides a quantitative description of the phenomenon of metastability in open quantum systems. I will also explain how metastability relates to the separation in the real part of the master operator spectrum and connect to earlier results of the spectral theory of metastability [2].
[1] arXiv:2104.05095 (2021).
[2] Phys. Rev. Lett. 116, 240404 (2016).
Metastability is a phenomenon of a large separation in dynamical timescales, leading to a prolonged temporal regime when system states appear stationary before eventually relaxing towards a true, usually unique, steady state. For classical equilibrium dynamics, metastability can be understood as a consequence of multiple local minima present in the system free energy function, but for non-equilibrium dynamics such a general description linking dynamic and static properties is elusive. In this talk, I will introduce an information-theoretic approach of quantifying how non-stationary an open quantum system is during a given time regime [1]. Despite its abstractness, this approach arises directly from experimental considerations of how the averages of observables change with time in a finitely dimensional system. For dynamics governed by a master equation, I will then draw upon a simple but powerful analogy with exponential decay, to investigate regimes when such changes are negligible according to the logarithmic scale of time, and thus the system can be viewed as approximately stationary. I will show that a distinct regime of approximate stationarity may arise beyond the initial and final regimes of the dynamics, which provides a quantitative description of the phenomenon of metastability in open quantum systems. I will also explain how metastability relates to the separation in the real part of the master operator spectrum and connect to earlier results of the spectral theory of metastability [2].
[1] arXiv:2104.05095 (2021).
[2] Phys. Rev. Lett. 116, 240404 (2016).
2021-05-27 (Thursday)
join us at 11:15
Sofiane Merkouche (University of Oregon)Multimode entanglement swapping via spectrally-resolved measurements
2021-05-20 (Thursday)
join us at 11:15
Marek Czachor (Politechnika Gdańska)Faking quantum probabilities: Beyond Bell's theorem and Tsirelson bounds
2021-05-13 (Thursday)
join us at 11:15
Mateusz Mazelanik (QOT UW)Super-resolution spectrometer based on a quantum memory using frequency-domain inversion interferometry
2021-05-06 (Thursday)
join us at 11:15
Francesco Albarelli (IFT UW)Probe incompatibility in multiparameter noisy quantum channel estimation
2021-04-29 (Thursday)
join us at 11:15
Ofer Firstenberg (Weizmann Institute)Quantum nonlinear optics with Rydberg atoms
Zoom link: https://zoom.us/j/6526721604?pwd=Y0pPdE9vT1hNWWNiZVBMaEVOeHN2dz09
Optical nonlinearities at the few-photon level bring together the fields of quantum optics and nonlinear optics. This regime, so-called quantum nonlinear optics, is described by effective strong interactions between individual photons. I will introduce the basic concepts and the original experiments realizing this regime using ultracold Rydberg atoms. I will overview recent achievements and outstanding proposals, including photon crystallization and the generation of photonic cluster states.
Optical nonlinearities at the few-photon level bring together the fields of quantum optics and nonlinear optics. This regime, so-called quantum nonlinear optics, is described by effective strong interactions between individual photons. I will introduce the basic concepts and the original experiments realizing this regime using ultracold Rydberg atoms. I will overview recent achievements and outstanding proposals, including photon crystallization and the generation of photonic cluster states.
2021-04-22 (Thursday)
join us at 11:15
Stanisław Kurdziałek (IFT UW)Back to sources—the role of coherence in super-resolution imaging revisited
Zoom link: https://zoom.us/j/6526721604?pwd=Y0pPdE9vT1hNWWNiZVBMaEVOeHN2dz09
The fundamental limit on the precision of the separation estimation between two partially coherent sources is derived. Photon losses, inevitably associated with imperfect imaging, are properly taken into account. We begin our analysis with a simple and common imaging model based on the 4f system. We then show that our results are valid for any passive, linear, translationally invariant optical imaging system. We obtain the expression for the Quantum Fisher Information, which is consistent with the already computed classical Fisher Information and latest experimental work. We also identify the source of discrepancies in the results obtained earlier and show how to correctly interpret them
The fundamental limit on the precision of the separation estimation between two partially coherent sources is derived. Photon losses, inevitably associated with imperfect imaging, are properly taken into account. We begin our analysis with a simple and common imaging model based on the 4f system. We then show that our results are valid for any passive, linear, translationally invariant optical imaging system. We obtain the expression for the Quantum Fisher Information, which is consistent with the already computed classical Fisher Information and latest experimental work. We also identify the source of discrepancies in the results obtained earlier and show how to correctly interpret them
2021-04-15 (Thursday)
room 1.03, Pasteura 5 at 11:15
Nathan Shettell (CNRS, Sorbonne Universite, Paris)Cryptographically enhanced Quantum Metrology
Zoom link: https://zoom.us/j/6526721604?pwd=Y0pPdE9vT1hNWWNiZVBMaEVOeHN2dz09
Quantum metrology is widely accepted as one of the most advanced pillars of quantum information, where quantum effects lead to enhanced precision measurements of unknown quantities. On the other hand, quantum cryptography uses quantum systems to detect and avoid the effects of malicious behaviour. In the future, where quantum devices are more accessible, and quantum tasks are delegated to third parties, it is natural to want to combine these fields, to ensure that any quantum metrology process occurs in a secure manner. In this seminar, I will discuss the framework of quantum metrology enhanced with quantum cryptography. In particular, I will show that the performance from a metrology perspective can be directly linked to the soundness of a cryptographic protocol. Additionally, I discuss the cryptographic protocols we developed in [Shettell-Kashefi-Markham 2021] for quantum metrology in the presence of a malicious adversary.
Quantum metrology is widely accepted as one of the most advanced pillars of quantum information, where quantum effects lead to enhanced precision measurements of unknown quantities. On the other hand, quantum cryptography uses quantum systems to detect and avoid the effects of malicious behaviour. In the future, where quantum devices are more accessible, and quantum tasks are delegated to third parties, it is natural to want to combine these fields, to ensure that any quantum metrology process occurs in a secure manner. In this seminar, I will discuss the framework of quantum metrology enhanced with quantum cryptography. In particular, I will show that the performance from a metrology perspective can be directly linked to the soundness of a cryptographic protocol. Additionally, I discuss the cryptographic protocols we developed in [Shettell-Kashefi-Markham 2021] for quantum metrology in the presence of a malicious adversary.
2021-04-08 (Thursday)
join us at 11:15
Matteo Brunelli (Cavendish Laboratory, University of Cambridge)