Calendar of Physics Talks Vienna

Quantum many-body effects in quantum dots and wires
Speaker:Sabine Andergasse (Univesity of Vienna)
Abstract:The understanding of correlation effects and their impact on the quantum coherence is of fundamental importance in view of technological implementations of quantum computing schemes and nanoelectronic applications. Using recently developed renormalization-group approaches, we investigate the effect of Coulomb interactions in quantum dots and wires and their characteristic signatures in the spectral and transport properties. We provide examples for the rich many-body physics of simple model systems in and out of equilibrium, as well as challenging extensions to more complex systems as realized in experiments.
Date: Mon, 03.12.2012
Time: 17:30
Duration: 60 min
Location:Univ. of Vienna, Ernst-Mach Hörsaal, Boltzmanngasse 5, 2nd floor, 1090 Wien
Contact:Dr. Christiane Losert / Univ. of Vienna

Phase Diagram and the Equation of State for the Covariant Chiral Quark Models
Speaker:Sanjin Benic (Zagreb University)
Abstract:Models of QCD are still very much welcome not only to try and interpret lattice data, but also provide insight into the (presently) unaccessible territory. Amongst these, the non-local version of the Nambu Jona-Lasinio (nlNJL), supplemented by the Polyakov loop, is able to keep contact with the lattice in the sense of the strong infrared running of the quark propagator invariants. We outline the QCD phase diagram in these studies, and the Equation of State as is relevant not only for lattice comparison but also, for example, the hydrodynamical calculations of the properties of the quark gluon plasma generated in heavy ion collisions, or the possible quark matter deep in the cores of neutron stars.
Date: Tue, 04.12.2012
Time: 12:30
Duration: 60 min
Location:Univ. of Vienna, Faculty of Physics, Boltzmanngasse 5, 5th floor, Erwin Schrödinger Lecture Hall
Contact:F. Brünner, S. Frank, P. Köhler, A. G. Passegger, S. Stetina - www.univie.ac.at/lunch-seminar

Matrix models and matrix geometries
Speaker:Harold Steinacker (Univ.Wien)
Abstract:im Rahmen des Seminars für Mathematische Physik
Date: Tue, 04.12.2012
Time: 14:15
Duration: 60 min
Location:Fakultät für Physik, Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:J. Yngvason

Quantum Monte Carlo-Stochastic Series Expansion; from coding to the simulation of NMR spectra
Speaker:Dipl.-Ing. Robert Achleitner (Technische Universität Wien, Institut für Angewandte Physik)
Abstract:SrCu2O3 is a spin-1/2 Heisenberg spin-ladder compound that has been studied intensely both experimentally and theoretically. However, the low temperature broadening of the NMR spectrum caused by a small impurity concentrations (x < 0.005) could not be explained satisfactorily. During my talk I will describe how such a system can be modeled and simulated using "Quantum Monte Carlo" (QMC) in the framework of the "Stochastic Series Expansion" (SSE). A brief introduction about the Monte Carlo Method in general will provide a basic understanding of this powerful tool. After discussing the stochastic series expansion the algorithm applied to the spin-1/2 Heisenberg model will be presented. In the last part of the talk I will show results obtained with our QMC-SSE code as well as a semi empirical model obtained from these results.
Date: Tue, 04.12.2012
Time: 16:00
Location:Technische Universität Wien, Institut für Angewandte Physik, Seminarraum 134A, Turm B (gelbe Leitfarbe), 5. OG, 1040 Wien, Wiedner Hauptstraße 8-10
Contact:Ao.Univ.Prof. Dr. Peter Mohn

Towards nonexistence of electrovacuum stationary black holes with multiple components
Speaker:Willie Wong (EPFL Lausanne)
Abstract:im Rahmen des Literaturseminars
Date: Wed, 05.12.2012
Time: 14:15
Duration: 60 min
Location:Arbeitsgruppe: Gravitation, Währinger Strasse 17, Seminarraum A, 2. Stock
Contact:P. Chrusciel

Neutrino masses in multi-Higgs doublet models
Speaker:Alejandro Ibarra (Technical Univ. Munich)
Abstract:im Rahmen des Teilchenphysikseminars
Date: Thu, 06.12.2012
Time: 14:15
Duration: 60 min
Location:Fakultät für Physik, Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:W. Grimus, H. Neufeld

Coherent control of strongly coupled nanomechanical systems
Speaker:Eva WEIG (Center for NanoScience & Faculty of Physics, Ludwig-Maximilians-University of Munich)
Abstract:Nanomechanical resonators are freely suspended bridges with nanoscale diameters which can be driven to vibrate under resonant actuation. These nanostructures are receiving an increasing amount of attention both in fundamental experiments and sensing applications for their remarkable mechanical properties. However, the investigation of nanomechanical systems calls for novel transduction mechanisms to actuate and detect their motion, for integrated control and tuning schemes as well as a fundamental understanding of the underlying dissipation mechanisms to enable high mechanical quality factors. In this presentation, I will show how the above requirements can be met using doubly-clamped pre-stressed silicon nitride string resonators, which are explored as high Q nanomechanical systems (NEMS), enabling room temperature quality factors of several 100,000 in the 10 MHz eigenfrequency range. We employ electrically induced gradient forces to implement dielectric transduction as an efficient way to actuate and probe these nanomechanical resonators and to control the resonator eigenfrequency [1]. Choosing an appropriate sample geometry allows to engineer inverse tuning behaviour of the two orthogonal fundamental flexural modes of the string. Thus, both modes can be tuned into resonance where a pronounced avoided crossing is observed. The extracted coupling strength is much larger than the linewidth of the mechanical resonances indicating that the system is clearly in the strong-coupling regime [2]. This allows to employ the device as a classical nanomechanical model system to demonstrate non-adiabatic Landau-Zener dynamics [3]. A pulsed measurement scheme is used to analyze the time-dependent evolution of a previously initialized mode as it is swept across the coupling region. At lower sweep rates, the system adiabatically follows the energy eigenstates, whereas the energy is transferred from one branch to the other during very fast sweeps. The measured transition probabilities show an excellent quantitative agreement with the Landau-Zener theory. The observed energy relaxation time exceeds the length of the manipulation pulses, demonstrating coherent control of the system. 1. J. Rieger, T. Faust, M. J. Seitner, J. P. Kotthaus, E. M. Weig, Appl. Phys. Lett. 101, 103110 (2012). 2. T. Faust, J. Rieger, M.J. Seitner, P. Krenn, J.P. Kotthaus, E.M. Weig, Phys. Rev. Lett. 109, 037205 (2012). 3. L. D. Landau, Phys. Z. Sowjetunion 2, 46 (1932); C. Zener, Proc. R. Soc. London, Ser. A 137, 696 (1932); E. C. G. Stueckelberg, Helv. Phys. Acta 5, 369 (1932); E. Majorana, Nuovo Cim. 9, 43 (1932).
Date: Fri, 07.12.2012
Time: 15:30
Location:Atominstitut, Hörsaal, Stadionallee 2, 1020 Wien
Contact:Johannes Majer