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Calendar of Physics Talks Vienna
| A Minimal Solvable Model of Many-Body Quantum Chaos |
| Speaker: | Tomaz Prosen (U of Ljubljana) |
| Abstract: | I will describe a simple model of locally interacting quantum spin 1/2 chain, namely Floquet-Ising chain with transverse and longitudinal fields, where the spectral form factor can be computed exactly (in the thermodynamic limit) due to a particular space-time duality symmetry of the model, and shown to match the prediction of Random Matrix Theory. Our result implies ergodicity for any finite amount of disorder in the longitudinal field, rigorously excluding the possibility of many-body localization in the model.
Reference: B. Bertini, P. Kos, and T. Prosen, arXiv:1805.00931
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| Date: | Tue, 22.05.2018 |
| Time: | 11:00 |
| Location: | ESI, Boltzmann Lecture Hall |
| Contact: | secr@esi.ac.at |
| Structure analysis of two-dimensional oxide quasicrystal in physical and internal space |
| Speaker: | Stefan Förster (Martin-Luther-Universität Halle-Wittenberg, Institute of Physics, Halle/Germany) |
| Abstract: | Recently the formation of BaTiO3-derived and SrTiO3-derived two-dimensional oxide quasicrystals (OQC) with 12-fold symmetry have been discovered on Pt(111) substrates [1,2]. The characteristic Niizeki-Gähler tiling formed by these OQCs consists of quadratic, triangular, and rhombic elements of equal side length with Ti atoms at the vertices. This tiling can be derived from cutting a periodic hyperhexagonal structure in the four-dimensional space and projecting it back into two dimensions. This main projection leads to the so-called physical space of the tiling which is embedded in the atomic lattice. An alternative projection of the four-dimensional lattice leads to a limited region in two dimensions, the so-called acceptance region in the internal space. |
| Date: | Tue, 22.05.2018 |
| Time: | 16:00 |
| Location: | Technische Universität Wien, Institut für Angewandte Physik, E134 yellow tower „B“, 5th floor, Sem.R. DB gelb 05 B (room number DB05L03), 1040 Wien, Wiedner Hauptstraße 8-10 |
| Contact: | Univ.Prof. Dr. Ulrike Diebold |
| Transport signatures of transient superfluids |
| Speaker: | Aditi Mitra (CUNY ) |
| Abstract: | Recent advances in ultra-fast measurement in cold atoms, as well as pump-probe spectroscopy of K3C60 films, have opened the possibility of rapidly quenching systems of interacting fermions to, and across, a finite temperature superfluid transition. However, determining that a transient state has approached a second-order critical point is difficult, as standard equilibrium techniques are inapplicable. We show that the approach to the superfluid critical point in a transient state may be detected via time-resolved transport measurements, such as the optical conductivity. We leverage the fact that quenching to the vicinity of the critical point produces a highly time dependent density of superfluid fluctuations, which affect the conductivity in two ways. Firstly, by inelastic scattering between the fermions and the fluctuations, and secondly by direct conduction through the fluctuations. T |
| Date: | Wed, 23.05.2018 |
| Time: | 11:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Universality and quantum criticality of the one-dimensional spinor Bose gas |
| Speaker: | Andreas Klümper (Bergische Universität Wuppertal) |
| Abstract: | We investigate the universal thermodynamics of the two-component one-dimensional Bose gas with contact interactions in the vicinity of the quantum critical point separating the vacuum and the ferromagnetic liquid regime. We find that the quantum critical region belongs to the universality class of the spin-degenerate impenetrable particle gas which, surprisingly, is very different from the single-component case and identify its boundaries with the peaks of the specific heat. In addition, we show that the compressibility Wilson ratio, which quantifies the relative strength of thermal and quantum fluctuations, serves as a good discriminator of the quantum regimes near the quantum critical point. Remarkably, in the Tonks-Girardeau regime the universal contact develops a pronounced minimum, reflected in a counterintuitive narrowing of the momentum distribution as we increase the temperature. |
| Date: | Thu, 24.05.2018 |
| Time: | 11:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Stochastic Approach to Non-Equilibrium Quantum Spin Systems |
| Speaker: | Joe Bhaseen (Kings College London) |
| Abstract: | We discuss a stochastic approach to non-equilibrium quantum spin systems based on recent insights linking quantum and classical dynamics. Exploiting a sequence of exact transformations, quantum expectation values can be recast as averages over classical stochastic processes. We illustrate this approach for the quantum Ising model by extracting the Loschmidt amplitude and the magnetization dynamics from the numerical solution of stochastic differential equations. We show that dynamical quantum phase transitions are accompanied by clear signatures in the associated classical distribution functions, including the presence of enhanced fluctuations. We demonstrate that the method is capable of handling integrable and nonintegrable problems in a unified framework, including those in higher dimensions.
[1] S. De Nicola, B. Doyon and M. J .Bhaseen; arXiv:1805.05350 |
| Date: | Fri, 25.05.2018 |
| Time: | 11:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
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