Seminarium Fizyki Materii Skondensowanej
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 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
2019-06-14 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15 
Nicolas Dupuis (Sorbonne Univ. & CNRS, Paris)Bose-glass phase of a one-dimensional disordered Bose gas
We study a one-dimensional disordered Bose fluid using bosonization, the replica method and a nonperturbative functional renormalization-group approach. We find that the (localized) Bose-glass phase is described by a fully attractive strong-disorder fixed point characterized by a singular disorder correlator whose functional dependence assumes a cuspy form. We show that this reveals the glassy properties (pinning, ``shocks'' and ``avalanches'') of the Bose-glass phase due to the existence of metastable states, as well as the crucial role of quantum tunneling between different metastable configurations leading to the existence of rare superfluid regions.
2019-06-07 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Katarzyna Roszak (Politechnika Wrocławska)How to detect qubit environment entanglement in pure dephasing evolutions
We propose a straightforward experimental protocol to test whether qubit-environment entanglement is generated during pure dephasing of a qubit. The protocol is implemented using only measurements and operations on the qubit – it does not involve the measurement of the system-environment state of interest, but the preparation and measurement of the qubit in two simple variations. A difference in the time dependences of qubit coherence between the two cases testifies to the presence of entanglement in the state of interest. Furthermore, it signifies that theenvironment-induced noise experienced by the qubit cannot be modeled as a classical stochastic process independent of the qubit state. We demonstrate the operation of this protocol on a realistically modeled nitrogen vacancy center spin qubit in diamond interacting with a nuclear spinenvironment, and show that the generation of entanglement should be easily observable in this case.
2019-05-31 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Oleksandr Gamayun (University of Amsterdam)Relaxation in classical integrable systems
I will consider non-equilibrium dynamics in the classicalintegrable systems. Integrability techniques allow finding the exactform of the large time asymptotic profile, which I will present as ananalog of the Eigenstate State Thermalization Hypothesis. My mainexamples will be relaxation dynamics in one-dimensional Bose gases,formulated as an initial value problem for the classical nonlinearSchrodinger equation and domain wall "melting " in XXZ magnetic. Inthe latter case, I show a quantitative agreement with quantum results.
2019-05-24 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Thomas Sturges (IFT WF UW)Localisation of Microcavity Polaritons
In closed systems, thermodynamics foresees that all evolutions lead to an equilibrium state. However this notion was recently challenged by the demonstration of many-body localisation, which arises among the interplay of disorder-induced localisation and many-body interactions. We ask the question: can a localised phase exist in an open, interacting, driven-dissipative system. In collaboration with an experimental group from EPFL we demonstrate the localisation of microcavity polaritons, as witnessed by the inverse participation-ratio.
2019-05-17 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Bertrand Delamotte (Paris VI)Surprises in the O(N) models or why might the standard large N analysis fail
The O(N) models are probably the most studied field theories. Everything is supposed to be known about their symmetric and symmetry broken phases as well as their critical behavior. Many analytical methods were born here and it is the textbook example for both the $\epsilon=4-d$ and the large-$N$ expansions. We nevertheless show that several renormalization group fixed points of this model were not found by the usual methods. These new fixed points are relevant for the multicritical physics of the O(N) models.We also show that the $N\to\infty$ limit was not able to identify them because of an implicit analyticity prerequisite of this method that turns out to be wrong. The functional and nonperturbative renormalization group plays a key role to find them.
2019-04-26 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Dieter Vollhardt (University of Augsburg)What do we learn from the observation of an isosbestic point?
In physics, chemistry and biology it is often observed that the curves of a physical quantity f(x,p) cross at one or more points, when plotted as a function of x for different values of some parameter p. Sometimes these crossing points are confined to a remarkably narrow region, or are even located at a single point called "isosbestic point". For example, isosbestic points are found in the curves of the specific heat of many correlated electron systems, as well as in their photoemission spectrum, reflectivity, and Raman response. I will show that isosbestic points always provide valuable information about the system in which they occur.
2019-04-12 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Gabriel Wlazłowski (Politechnika Warszawska)From dynamics of a single vortex to quantum turbulence in fermionic superfluids
Quantized vortices are a hallmark of superfluids. Their generation, dynamics, evolution, and eventual decay have been studied experimentally for some six decades in liquid He and recently in Bose and Fermi cold atom systems. While life cycle of quantized vortices in Bose systems can be described by simple Gross-Pitaevskii equation, Fermi systems are more demanding where satisfactory description requires inclusion of many mechanisms for superfluid relaxation like various phonon processes or Cooper pair breaking. In this talk I will show that time-dependent superfluid density functional theory in natural manner incorporates all these necessary ingredients. Recently, the framework has been extended to spin-imbalanced systems, which allows us to study the superfluid dynamics in new regime where both superfluid and normal components coexist even at zero temperature limit. I will present numerical results for formation and dynamics of a superfluid vortex in the unitary Fermi gas, both in spin balanced and imbalanced cases. Next, I will show that ultra-cold fermionic atoms may provide a new platform for studies of quantum turbulence, accessible to both experiment and theory.
2019-04-05 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Maciej Lisicki (IFT UW)Pumping and swimming: two faces of phoretic flows
Janus particles with the ability to move phoretically in self-generated chemical concentration gradients are model systems for active matter. On the other hand, chemically active surfaces can lead to microscale flow generation, bacoming an effective pumping mechanism in inertia-less small-scale flows. In this talk, I will review briefly both phenomena relating to the same concept of phoretic flow generation. Asymmetry needed for the flow to be initiated can be induced by geometry or by chemical patterning. I will show examples of both ways and some applications in biomimetic systems of fully three-dimensional phoretic swimmers.
2019-03-22 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Maciej Maśka (Uniwersytet Śląski)Topofilia: a self-adjusted topological state in a chain of magnetic atoms
It is known that a chain of magnetic moments deposited on a bulk superconductor self-organizes into a helical structure. The ordering is driven by an effective RKKY-type interaction that is mediated by itinerant electrons. It is interesting that for wide range of system parameters the wave vector characterizing the helix self-tunes to support a topological state with Majorana edge modes. This feature has been demonstrated in the ground state, also in the presence of some forms of disorder. In this work we study the stability of this self-organized topological state at finite temperatures. We show how the correlation length of the spiral order decreases with increasing temperature. In most cases the destruction of the helical order drives the system into a topologically trivial state. For some parameters, however, the topological state survives up to very high temperatures despite the absence of the helical order.
2019-03-15 (Piątek)
Zapraszamy do sali 1.02, ul. Pasteura 5 o godzinie 12:15
Axel Cortes Cubero (Utrecht University)Systems that should thermalize, but don't
In general, many-body systems out of equilibrium should eventually thermalize: the system should "forget" the details of the initial state and be well described by statistical mechanics at large times.Well known counter examples are given by "integrable" systems, which have a large number of conserved quantities, that prevent the system from forgetting about the initial state. Can similar non-thermalization occur in manifestly non-integrable systems? Probably yes, we show.