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

Elements of the general boundary formulation and the composition of local measurements in quantum field theory

Date: czwartek, 1 czerwca, 2023
Time: 11:00
Host: ICTQT Seminar, room 215
Zoom link: https://zoom.us/j/91536504866?pwd=SkkvVDByRmlmRTBWNGxWVlIzd0hFdz09

Speaker: Adamantia Zampeli (Universidad Nacional Autónoma de México, Morelia)

Abstract In this talk, I will introduce the main elements and ideas of the general boundary formulation [R. Oeckl. A local and operational framework for the foundations of physics. Advances in Theoretical and Mathematical Physics, 23(2):437–592, 2019. arXiv: 1610.09052.]. This is a formalism inspired by quantum gravity approaches and quantum information theoretic ideas and it generalises quantum field theory in such a way to deal with local measurements in local spacetime regions. It can therefore serve as a framework for reconciling quantum field theory with quantum information theory and describe measurement set-ups more general that the scattering (S-matrix) picture of particle physics. This is known to be non-trivial because the naïve application on quantum fields of mathematical objects representing measurements in the non-relativistic theory can lead to violations of locality and causality. This has been indicated by the Reeh-Schlieder theorem, as well as the more recent analysis by Sorkin [R. D. Sorkin. Impossible measurements on quantum fields. In B. L. Hu and T. A. Jacobson, editors, Directions in General Relativity: Papers in Honor of Dieter Brill, Volume 2, volume 2, page 293, January 1993.]. Here, I will focus on the composition of measurements (and observables) in relativistic quantum field theory and discuss how we deal with this problem in the context of the general boundary formulation.

Semi-device independent nonlocality certification for near-term quantum networks

Date: środa, 31 maja, 2023
Time: 14:30
Host: Quantum Information and Quantum Computing Working Group, Meeting ID: 844 2780 6931
Zoom link: https://us06web.zoom.us/j/84427806931?pwd=ODBjZkNCUW94VUhCREFxbjRSeDBFdz09
Passcode: nisq

Speaker: Ana Costa (Federal University of Paraná)

Abstract Verifying entanglement between parties is essential for creating a secure quantum network, and Bell tests are the most rigorous method for doing so. However, if there is any signalling between the parties, then the violation of these inequalities can no longer be used to draw conclusions about the presence of entanglement. There is a pressing need to examine the role of signalling in quantum communication protocols from multiple perspectives, including communication security, physics foundations, and resource utilization while also promoting innovative technological applications. Here, we propose a semi-device independent protocol that allows us to numerically correct for effects of correlations in experimental probability distributions, caused by statistical fluctuations and experimental imperfections. Our noise robust protocol presents a relaxation of a tomography-based optimisation method called the steering robustness. The proposed protocol is numerically and experimentally analyzed in the context of random, misaligned measurements, correcting for signalling where necessary, resulting in a higher probability of violation compared to existing state-of-the-art inequalities. Our work demonstrates the power of semidefinite programming for entanglement verification and brings quantum networks closer to practical applications.

Quantum Foundations Meets Causal Inference

Date: środa, 31 maja, 2023
Time: 14:00
Host: ICTQT Seminar, room 319
Zoom link: https://zoom.us/j/91536504866?pwd=SkkvVDByRmlmRTBWNGxWVlIzd0hFdz09

Speaker: Robert Spekkens (Perimeter Institute for Theoretical Physics)

Abstract Can the effectiveness of a medical treatment be determined without the expense of a randomized controlled trial? Can the impact of a new policy be disentangled from other factors that happen to vary at the same time? Questions such as these are the purview of the field of causal inference, a general-purpose science of cause and effect, applicable in domains ranging from epidemiology to economics. Researchers in this field seek in particular to find techniques for extracting causal conclusions from statistical data. Meanwhile, one of the most significant results in the foundations of quantum theory—Bell’s theorem—can also be understood as an attempt to disentangle correlation and causation. Recently, it has been recognized that Bell’s 1964 result is an early foray into the field of causal inference and that the insights derived from almost 60 years of research on his theorem can supplement and improve upon state-of-the-art causal inference techniques. In the other direction, the conceptual framework developed by causal inference researchers provides a fruitful new perspective on what could possibly count as a satisfactory causal explanation of the quantum correlations observed in Bell experiments. Efforts to elaborate upon these connections have led to an exciting flow of techniques and insights across the disciplinary divide. This talk will explore what is happening at the intersection of these two fields.

Limits of computation  – ultimate computers and computational nature of Black Holes – Part I

Date: poniedziałek, 29 maja, 2023
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us05web.zoom.us/j/89601291160?
Passcode: please contact albertrico23 at gmail.com

Speaker: Paweł Rykała  (Faculty of Physics, UJ)

Easy-to-compute local Clifford invariant for graph states

Date: poniedziałek, 15 maja, 2023
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us05web.zoom.us/j/89601291160?
Passcode: please contact albertrico23 at gmail.com

Speaker: Adam Burchard (Amsterdam)

Abstract Graph states are a cornerstone of quantum information theory. Existing invariants characterizing the local Clifford (LC) equivalence classes of graph states are however computationally inefficient and call for a more tractable approach. This paper introduces the foliage partition, an easy-to-compute LC-invariant of computational complexity O(n^3) in the number of qubits. Inspired by the foliage of a graph, our invariant has a natural graphical representation in terms of leaves, axils, and twins. It captures both, the connection structure of a graph and the $2$-body marginal properties of the associated graph state. We relate the foliage partition to the size of LC-orbits and use it to bound the number of LC-automorphisms of graphs. We also show the invariance of the foliage partition when generalized to weighted graphs and qudit graph states.

Studies on the creation and destruction of coherence by quantum channels

Date: środa, 26 kwietnia, 2023
Time: 15:00
Host: Quantum Information and Quantum Computing Working Group, Meeting ID: 844 2780 6931
Zoom link: https://us06web.zoom.us/j/84427806931?pwd=ODBjZkNCUW94VUhCREFxbjRSeDBFdz09
Passcode: nisq

Speaker: Masaya Takahashi (CFT-PAN)

Abstract I will talk about the studies on the creation and destruction of coherence by quantum channels. First, we will see how decoherence appears in matrix form through an example of a phase-damping channel on one qubit. This provides a qualitative perspective, serving as a good starting point. Next, we will briefly review the resource theory of coherence, explaining the basic framework and notion. To understand the ability of quantum channels to generate coherence, we begin by considering the cohering power and generalized cohering power of channels. These quantifiers have important operational meaning: the cohering power of a channel represents the minimum coherence in a state required to simulate the channel with incoherent channels. If the employed coherence quantifier is subadditive, the minimum coherence coincides with the generalized cohering power. This suggests that we can regard quantum coherence in a state plus incoherent operations as a quantum channel. It is natural to consider the reverse direction: can we identify a quantum channel as a resource of coherence? We will see a positive answer to this question by demonstrating that another type of measure, coherence generating capacity, quantifies how much maximally coherent state can be generated by a given channel and incoherent operations. The coherence-generating capacity is bounded by or equal to complete cohering power, which has a similar expression to generalized cohering power but is defined by taking into account coherence generation in the environment as well. I will present that complete cohering power and generalized cohering power are equal, which is also published in my earlier work. In that paper, I also introduced completed decohering power defined in a similar way to study decoherence with taking into account decoherence in the environment as well too. I will show that, in some cases, entanglement between the system and environment enhances decoherence, which does not occur in the creation of coherence. Finally, I provide some ideas for future applications.

Quantum control and semi-classical quantum gravity

Date: środa, 26 kwietnia, 2023
Time: 12:30
Host: CENTER FOR THEORETICAL PHYSICS COLLOQUIUM
Zoom link: https://zoom.us/j/82380380442?pwd=Z3IyeEhlZmFHU1B2M2VUVVJhODkrUT09
Passcode: 134595

Speaker: Lajos Diósi (Wigner Research Center for Physics & Eötvös Loránd University)

Abstract Quantum gravity has not yet obtained a usable theory. We apply the semiclassical theory instead, where the space-time remains classical (i.e.: unquantized). However, the hybrid quantum-classical coupling is acausal, violates both the linearity of quantum theory and the Born rule as well. Such anomalies can go away if we modify the standard mean-field coupling, building on the mechanism of quantum measurement and feed-back well-known in, e.g., quantum optics. The Newtonian limit can fully be worked out, it leads to the gravity-related spontaneous wave function collapse theory of Penrose and the speaker.

The interplay between quantum dynamics and the environmental form of quantum channels

Date: poniedziałek, 24 kwietnia, 2023
Time: 14:15
Host: Quantum Chaos and Quantum Information (Jagiellonian University)
Zoom link: https://us05web.zoom.us/j/89601291160?
Passcode: please contact albertrico23 at gmail.com

Speaker: Frederik vom Ende (Freie Universität Berlin)

What is Nonclassical about Uncertainty Relations?

Date: środa, 19 kwietnia, 2023
Time: 14:30
Host: Quantum Information and Quantum Computing Working Group, Meeting ID: 844 2780 6931
Zoom link: https://us06web.zoom.us/j/84427806931?pwd=ODBjZkNCUW94VUhCREFxbjRSeDBFdz09
Passcode: nisq

Speaker: Giovanni Scala (ICTQT – Univerisity of Gdańsk)

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 perspective 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 its predictability tradeoff describes a section of a circle 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.

Quantum sensors operated in real time

Date: środa, 19 kwietnia, 2023
Time: 12:30
Host: CENTER FOR THEORETICAL PHYSICS COLLOQUIUM
Zoom link: https://zoom.us/j/82380380442?pwd=Z3IyeEhlZmFHU1B2M2VUVVJhODkrUT09
Passcode: 134595

Speaker: Jan Kołodyński (Centre of New Technologies (CeNT), University of Warsaw)

Abstract From gravitational-wave detectors to cryogenically cooled nanoresonators, quantum effects have been shown to enhance capabilities of various devices in sensing external perturbations. Although this fact has led to important breakthroughs in the field of quantum metrology, one often forgets that the vast majority of real-life applications require quantum sensors to track signals that vary over time—e.g., gravitational waves generated by black holes merging, or fluctuating magnetic fields generated by the human brain. In my talk, I will summarise recent results obtained with my group, in which we combine the description of continuously monitored quantum sensors with methods of statistical inference, so that quantum effects can still be used to boost their sensitivity in “real time”. Firstly, I will focus on an optomechanical sensor operated in the non-linear regime, in order to show how the non-classical correlations of photons being emitted may then enhance the sensitivity after resorting to Bayesian inference. Secondly, I will consider the setting of optically pumped atomic magnetometers, in which case I will demonstrate that it is enough to use less demanding methods of (Extended) Kalman Filtering and measurement-based feedback in order to maintain the quantum-enhanced sensitivity or, in other words, drive the atomic ensemble into a highly entangled (spin-squeezed) state tailored to efficiently track a fluctuating magnetic field.
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