Causal limit on quantum communication
Zapraszamy w środę 26.02.2020 o godz. 10:15, sala 361 na seminarium.
Seminarium pod tytułem: "Causal limit on quantum communication" poprowadzi Robert Pisarczyk, University of Oxford
The capacity of a channel is known to be equivalent to the highest rate at which it can generate entanglement. Analogous to entanglement, the notion of a causality measure characterizes the temporal aspect of quantum correlations. Despite holding an equally fundamental role in physics, temporal quantum correlations have yet to find their operational significance in quantum communication. Here we uncover a connection between quantum causality and channel capacity. We show the amount of temporal correlations between two ends of the noisy quantum channel, as quantified by a causality measure, implies a general upper bound on its channel capacity. The expression of this new bound is simpler to evaluate than most previously known bounds. We demonstrate the utility of this bound by applying it to a class of shifted depolarizing channels, which results in improvement over previously known bounds for this class of channels.
Quantifying memory capacity as a quantum thermodynamic resource
Zapraszamy w środę 19.02.2020 o godz. 10:15, sala 361 na seminarium.
Seminarium pod tytułem: "Quantifying memory capacity as a quantum thermodynamic resource " poprowadzi Tanmoy Biswas, ICTQT
The information-carrying capacity of a memory is known to be a thermodynamic resource facilitating the conversion of heat to work. Szilard's engine explicates this connection through a toy example involving an energy-degenerate two-state memory. We devise a formalism to quantify the thermodynamic value of memory in general quantum systems with nontrivial energy landscapes. Calling this the thermal information capacity, we show that it converges to the non-equilibrium Helmholtz free energy in the thermodynamic limit. We compute the capacity exactly for a general two-state (qubit) memory away from the thermodynamic limit, and find it to be distinct from known free energies. We outline an explicit memory--bath coupling that can approximate the optimal qubit thermal information capacity arbitrarily well.
Kolmogorov consistency as a quantumness witness for external system
Zapraszamy w środę 12.02.2020 o godz. 10:15, sala 361 na seminarium.
Seminarium pod tytułem: "Kolmogorov consistency as a quantumness witness for external system" poprowadzi Fattah Sakuldee, ICTQT
We study the classicality of a finite quantum system, called environment, defined by commutativity of the associate operator algebra, given sequential measurements on the environment. We demonstrate by constructing a scheme of probing from the pure-dephasing-type interaction with a qudit and preparation-evolution-measurement protocol thereon, the weak measurement sequence on the studied environment can be induced and some characteristics of the environment can be extracted from measurement statistics. From the general measurements on the environment, we consider its Kolmogorov consistency, the situation when a shorter length joint probability can be extracted from the longer one by summing the missing all possible intermediate outcomes. We provide general criteria for equivalence between Kolmogorov consistency of the statistics for arbitrary measurements and commutativity property of operator algebra of the environment, and apply the criteria to show explicitly for the induced measurements. As a result, we show that Kolmogorov consistency of the probability can be considered as a quantumness witness for its corresponding operator algebra of the environment if the conditional Hamiltonians are all non-degenerate. For the qubit, the equivalence can be obtained in general if one considers two axes of measurements namely X and Y.
Open quantum systems and potential engineering
Zapraszamy w piątek 07.02.2020 o godz. 12:15, sala 361 na seminarium.
Seminarium pod tytułem: " Open quantum systems and potential engineering" poprowadzi Stefano Cusumano, NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR (Pisa)
As I will shortly move to ICTQT, in this talk I will try to give an overview of my work during the PhD. During this period I worked mainly on open quantum systems, applying collisional models to study both cascade systems (i.e. systems with a chiral propagation of information) and thermodynamic problems. On the other side, I also worked on potential engineering, that is, the design of potential profiles in order to obtain quantum states with specific properties or to perform specific tasks.
Quantum compilation using the ZX-calculus
Zapraszamy w środę 05.02.2020 o godz. 10:15, sala 361 na seminarium.
Seminarium pod tytułem: "Quantum compilation using the ZX-calculus " poprowadzi Dominic Horsman, Université Grenoble Alpes
In this talk I will give an introduction to the use of the ZX calculus of observables as a compilation language for quantum computing.
ZX calculus diagrams comprise a formal re-write language that allows purely diagrammatic equational reasoning for qubit quantum mechanics. I will give a basic introduction to the diagrams (no category theory required), and show how the calculus is especially suited to acting as an 'intermediate representation' for quantum compilers. This entails mediating between high-level user workloads/algorithms and qubit-level device specifications. I will go over recent work (both academic and commercial) on circuit optimisation using the calculus, and on its function as a design, verification, and optimisation language for error correction. I will finish by discussing insights the use of ZX gives into possible new models of quantum computation.
Zapraszamy w środę 29.01.2020 o godz. 10:15, sala 361 na seminarium.
Seminarium pod tytułem: "MIP*=RE" poprowadzi Máté Farkas, ICTQT UG
We show that the class MIP* of languages that can be decided by a classical verifier interacting with multiple all-powerful quantum provers sharing entanglement is equal to the class RE of recursively enumerable languages. Our proof builds upon the quantum low-degree test of (Natarajan and Vidick, FOCS 2018) by integrating recent developments from (Natarajan and Wright, FOCS 2019) and combining them with the recursive compression framework of (Fitzsimons et al., STOC 2019).
An immediate byproduct of our result is that there is an efficient reduction from the Halting Problem to the problem of deciding whether a two-player nonlocal game has entangled value 1 or at most 12. Using a known connection, undecidability of the entangled value implies a negative answer to Tsirelson's problem: we show, by providing an explicit example, that the closure Cqa of the set of quantum tensor product correlations is strictly included in the set Cqc of quantum commuting correlations. Following work of (Fritz, Rev. Math. Phys. 2012) and (Junge et al., J. Math. Phys. 2011) our results provide a refutation of Connes' embedding conjecture from the theory of von Neumann algebras.
Generalised uncertainty from geometric superpositions
Zapraszamy w piątek 24.01.2020 o godz. 12:15, sala 361 na seminarium.
Seminarium pod tytułem: "Generalised uncertainty from geometric superpositions" poprowadzi Prof. Matthew James Lake z Sun Yat-Sen University, Guangzhou, China.
Phenomenological approaches to quantum gravity implement a minimum resolvable length-scale but do not link it to an underlying formalism describing geometric superpositions. Here, we introduce an intuitive approach in which points in the classical spatial background are delocalised, or ‘smeared’, giving rise to an entangled superposition of geometries. The model uses additional degrees of freedom to parameterize the superposed backgrounds. Our formalism contains both minimum length and minimum momentum resolutions and we naturally identify the former with the Planck length. In addition, we argue that the minimum momentum is determined by the de Sitter scale, and may be identified with the effects of dark energy in the form of a cosmological constant. Within the new formalism, we obtain both the generalised uncertainty principle (GUP) and extended uncertainty principle (EUP), which may be combined to give an uncertainty relation that is symmetric in position and momentum. Crucially, our approach does not imply a significant modification of the position-momentum commutator, which remains proportional to the identity matrix. It therefore yields generalized uncertainty relations without violating the equivalence principle, in contradistinction to existing models based on nonlinear de Broglie relations. Implications for cosmology and prospects for future work on the smeared-space model are outlined.
Mechanizmy cholinergiczne śródmózgowia w indukcji hipokampalnego rytmu theta
Zapraszamy w czwartek 09.01.2020 o godz. 14:30, sala 361 na seminarium.
Seminarium pod tytułem: "Mechanizmy cholinergiczne śródmózgowia w indukcji hipokampalnego rytmu theta" poprowadzi dr hab. Jolanta Orzeł-Gryglewska.
Entropia wybranych parametrów hemodynamicznych w diagnostyce omdleń wazowagalnych
Zapraszamy w czwartek 19.12.2019 o godz. 14:30, sala 361 na seminarium.
Seminarium pod tytułem: "Entropia wybranych parametrów hemodynamicznych w diagnostyce omdleń wazowagalnych" poprowadzi dr Katarzyna Buszko (Wydział Framacji UMK).
Od przyczyny do skutku - poszukiwanie przyczynowości w układzie sercowo-naczyniowym człowieka metodami teorii informacji
Zapraszamy w czwartek 05.12.2019 o godz. 14:30, sala 361 na seminarium.
Seminarium pod tytułem: "Od przyczyny do skutku - poszukiwanie przyczynowości w układzie sercowo-naczyniowym człowieka metodami teorii informacji" poprowadzi Dorota Wejer (UG).