Is the mystery of wave-particle duality in quantum mechanics captured by Contextuality?
Zapraszamy w środę 01.07.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Is the mystery of wave-particle duality in quantum mechanics captured by Contextuality?" poprowadzi Giovanni Scala, University of Bari
Abstract: Wave-particle duality is considered to be one of the true misteries of quantum theory. However its core phenomenology can be reproduced by a local and noncontextual ontological model for particularly designed interferometric setup. Open is the question whether there is a connection between wave-particlle duality and contextuality in general scenarios. In this talk we focus on Englert's inequality that provides a quantitatively description of wave-particle duality in terms of visibility and distinguishability. The goal of this project is to explore whether contextuality is necessary for saturating the inequality for any values of visibility and distinguishability.
General Probabilistic Theories with a Gleason-type Theorem
Zapraszamy w środę 24.06.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "General Probabilistic Theories with a Gleason-type Theorem" poprowadzi Victoria Wright, UG / ICTQT
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.
Thermodynamics of Minimal Coupling Quantum Heat Engines
Zapraszamy w środę 10.06.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Thermodynamics of Minimal Coupling Quantum Heat Engines" poprowadzi Marcin Łobejko, UG / ICTQT
Abstract: The minimal-coupling quantum heat engine is a thermal machine consisting of an explicit energy storage system, heat baths, and a working body, which couples alternatively to subsystems through discrete steps - energy conserving two-body quantum operations. Within this paradigm, it is presented a general framework of quantum thermodynamics, where a process of the work extraction is fundamentally limited by a flow of non-passive energy (ergotropy), while energy dissipation is expressed through a flow of passive energy. The main result is finding the optimal efficiency and work extracted per cycle of the three-stroke engine with the two-level working body. One of key new tools is the introduced "control-marginal state" - one which acts only on a working body Hilbert space but encapsulates all the features of total working body-battery system regarding work extraction.
Device-independent quantum cryptography in the multipartite scenario
Zapraszamy w środę 03.06.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Device-independent quantum cryptography in the multipartite scenario" poprowadzi Gláucia Murta, Heinrich-Heine-Universitat Dusseldorf
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.
No Entropy Production in Quantum Thermodynamics
Zapraszamy w środę 20.05.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "No Entropy Production in Quantum Thermodynamics" poprowadzi Borhan Ahmadi
Abstract: I am going to give a controversial seminar concerning entropy production in quantum thermodynamics. I will show that there exists a fundamental difference between microscopic quantum thermodynamics and macroscopic classical thermodynamics. It will be proved that the entropy production in quantum thermodynamics always vanishes for both closed and open quantum systems! This novel and the very surprising result is derived based on the genuine reasoning Clausius used to establish the science of thermodynamics. This result will interestingly lead to defining the generalized temperature for any non-equilibrium quantum system.
(Semi-)device-independent certification of mutually unbiased bases
Zapraszamy w środę 13.05.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "(Semi-)device-independent certification of mutually unbiased bases" poprowadzi Máté Farkas, UG/ICTQT
As quantum technologies advance, the certification of high-dimensional quantum devices becomes more and more relevant. This is essential both for verifying the outcome of quantum computations, and for guaranteeing the security of cryptographic devices. In this talk, I will focus on the certification of quantum measurement devices performing measurements in mutually unbiased bases (MUBs) in arbitrary dimension. MUBs have a myriad of applications in quantum information processing, and therefore these measurement devices constitute basic building blocks of computational and cryptographic devices. I will discuss how to give a characterisation of MUBs that is suitable for semi-device-independent (SDI) certification, that is, certification under the assumption of fixed Hilbert space dimension. Then I will present a protocol that allows for experimental SDI certification of MUBs in arbitrary dimensions (that has since been demonstrated experimentally in dimension 4). Furthermore, I will discuss a relaxed device-independent (DI) characterisation of MUBs, referred to as mutually unbiased measurements (MUMs). While MUMs are strictly more general than MUBs, they share many operational characteristics, and I will present a protocol that allows for their DI certification.
Why standard entanglement theory is inappropriate for the study of Bell scenarios
Zapraszamy w środę 06.05.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Why standard entanglement theory is inappropriate for the study of Bell scenarios" poprowadzi David Schmid, University of Waterloo / Perimeter Institute
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.
Analiza toru oddechowego - podejście pierwsze
Zapraszamy w czwartek 07.05.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Analiza toru oddechowego - podejście pierwsze" poprowadzi dr Beata Graff (GUMed).
Chip-based measurement-device-independent quantum key distribution
Zapraszamy w środę 29.04.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Chip-based measurement-device-independent quantum key distribution " poprowadzi Akshata Shenoy, ICTQT UG
Abstract: Modern communication strives towards provably secure systems which can be widely deployed. Quantum key distribution provides a methodology to verify the integrity and security of a key exchange based on physical laws. However, physical systems often fall short of theoretical models, meaning they can be compromised through uncharacterized side-channels. The complexity of detection means that the measurement system is a vulnerable target for an adversary. Here, we present secure key exchange up to 200 km while removing all side-channels from the measurement system. We use mass-manufacturable, monolithically integrated transmitters that represent an accessible, quantum-ready communication platform. This work demonstrates a network topology that allows secure equipment sharing which is accessible with a cost-effective transmitter, significantly reducing the barrier for widespread uptake of quantum-secured communication.
Out-of-time-ordered correlation functions in open systems
Zapraszamy w piątek 24.04.2020 o godz. 14:00 na seminarium.
Seminarium ONLINE pod tytułem: "Out-of-time-ordered correlation functions in open systems" poprowadzi Jan Tuziemski, Stockholm University
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.