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The Cosmological Constant Puzzle - Symmetries of Quantum Fluctuations

Ostatnia modyfikacja: 
czwartek, 2 kwietnia 2020 roku, 16:33

Zapraszamy w piątek  27.03.2020 o godz. 12:00 na seminarium.

Seminarium ONLINE pod tytułem: "The Cosmological Constant Puzzle - Symmetries of Quantum Fluctuations" poprowadzi Steven Bass, UJ


The cosmological constant in Einstein's equations of General Relativity is a prime candidate to describe the dark energy that drives the accelerating expansion of the Universe and which contributes 69% of its energy budget. The cosmological constant measures the energy density of the vacuum perceived by gravitation. Experimentally, it is characterised by a tiny energy scale 0.002 eV. How should we understand this ? The quantum vacuum is described by particle physics where the mass scales that enter are very much larger. If one naively sums the zero-point energies of quantum fluctuations up to the energies where we do collider experiments at CERN then the cosmological constant comes out 10^60 times too large. Here we argue that the tiny value of the cosmological constant may be telling us something deep about the origin of symmetry in the subatomic world. The gauge symmetries which describe particle interactions may be emergent. The presentation will be given at Colloquium level and suitable for good Masters students.  



A primer on heat rectification

Ostatnia modyfikacja: 
czwartek, 2 kwietnia 2020 roku, 16:22

Zapraszamy w środę  18.03.2020 o godz. 10:15 na seminarium.

Seminarium ONLINE pod tytułem: "A primer on heat retification" poprowadzi Antonio Mandarino, ICTQT UG


The aim of this journal club talk will be the discussion of a topic that is getting more attention in the quantum thermodynamics community. In fact, numerous efforts, both theoretically and experimentally, are devoted to design technologies able to control and to route the heat flow in qubit systems suitable for the realization of quantum circuits.


Symmetries between measurements in quantum mechanics

Ostatnia modyfikacja: 
czwartek, 2 kwietnia 2020 roku, 15:55

Zapraszamy w środę  25.03.2020 o godz. 10:15 na seminarium.

Seminarium ONLINE pod tytułem: "Symmetries between measurements in quantum mechanics" poprowadzi Sebastien Designolle, University of Geneva


Symmetries are a key concept to connect mathematical elegance with physical insight. We consider measurement assemblages in quantum mechanics and show how their symmetry can be described by means of the so-called discrete bundles. It turns out that that many measurement assemblages used in quantum information theory as well as for studying the foundations of quantum mechanics are entirely determined by symmetry; moreover, starting from a certain symmetry group, novel types of measurement sets can be constructed. The insight gained from symmetry allows us to easily determine whether the measurements in the set are incompatible under noisy conditions, i.e., whether they can be regarded as genuinely distinct ones. In addition, symmetry allows to identify finite sets of measurements having a high sensitivity to reveal the quantumness of distributed quantum states.


Homologie persystentne w analizie zmienności rytmu serca

Ostatnia modyfikacja: 
wtorek, 10 marca 2020 roku, 13:10

Zapraszamy w czwartek 12.03.2020 o godz. 12:15, sala 361 na seminarium.

Seminarium pod tytułem: "Homologie persystentne w analizie zmienności rytmu serca" poprowadzi  dr hab. Grzegorz Graff, prof. PG.



Classical simulations of quantum circuits

Ostatnia modyfikacja: 
wtorek, 10 marca 2020 roku, 12:05

Zapraszamy w środę  11.03.2020 o godz. 10:15, sala 361 na seminarium.

Seminarium ONLINE pod tytułem: "Classical simulations of quantum circuits" poprowadzi Kamil KorzekwaUniversytet Jagielloński


It is of foremost importance, both from the foundational and technological point of view, to understand what components of the quantum theory are responsible for quantum supremacy, i.e. the potential ability of quantum computers to solve problems that cannot be solved efficiently on classical machines. One of the most promising ways to achieve this is to identify sub-theories of the quantum theory that can be efficiently simulated on classical computers, and the corresponding quantum resources (gates or states) that are responsible for the quantum speed-up. In this talk I will present the resource-theoretic approach to quantum computation, explain how it could be employed to develop a unified scheme for classical simulation of universal quantum circuits and, finally, I will describe a particular algorithm that allows one to simulate Clifford+T circuits with state-of-the-art run-time scaling.









Classical limits and contextuality in a scenario with multiple observers

Ostatnia modyfikacja: 
poniedziałek, 2 marca 2020 roku, 10:52

Zapraszamy w środę  04.03.2020 o godz. 10:15, sala 361 na seminarium.

Seminarium pod tytułem: "Classical limits and contextuality in a scenario with multiple observers" poprowadzi Roberto Baldijão, University of Campinas, IQOQI (Vienna)


Contextuality is regarded as a non-classical feature, challenging our everyday intuition; quantum contextuality is currently seen as a resource for many applications in quantum computation, being responsible for quantum advantage over classical analogs. In our work, we adapt the N-cycle scenarios with odd N to multiple independent observers which measure the system sequentially. We analyze the possibility of violating the inequalities as a function of the number of observers and under different measurement protocols. We then reinterpret the results as an open quantum system where the environment is divided into fractions. In this context, the results show the emergence of non-contextuality in such a setting, bringing together the quantum behavior to our classical experience. We then compare such emergence of non-contextuality with that of objectivity under the Quantum Darwinism process. We also take the opportunity to present recent developments in classical limits in Generalized Probabilistic Theories.








Applications of single photon technologies

Ostatnia modyfikacja: 
wtorek, 25 lutego 2020 roku, 8:51

Zapraszamy w piątek  28.02.2020 o godz. 12:15, sala 361 na seminarium.

Seminarium pod tytułem: Applications of single photon technologies"" poprowadzi Piotr Kolenderski, Single Photon Applications Laboratory  


Quantum communication offers a selection of methods for absolutely secure exchange of information. There are two particular links which are used in practice: fibers and free space. The latter implemented using satellites is more challenging, but offers substantially longer ranges.During my talk I will present two projects running in our lab at Nicolaus Copernicus University, which are related to satellite based quantum communication. The first one aims in building a ground station for a satellite receiver link. The second one is a joint effort with Syderal Polska and Gdansk University, where the goal is to build a satellite-grade polarization entanglement controller.







Causal limit on quantum communication

Ostatnia modyfikacja: 
wtorek, 25 lutego 2020 roku, 8:47

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

Ostatnia modyfikacja: 
poniedziałek, 17 lutego 2020 roku, 11:17

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

Ostatnia modyfikacja: 
poniedziałek, 10 lutego 2020 roku, 9:06

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.