
Calendar of Physics Talks Vienna
The interface pinning method 
Speaker:  Ulf R. Pedersen (Vienna University of Technology) 
Abstract:  An important aspect of computational condensed matter physics is the computation of phase diagrams. The thermodynamically stable phase is the one with the lowest Gibbs free energy. "Interface pinning" is a method where the Gibbs free energy differences between phases is computed directly in a single equilibrium simulation. This is done by applying an artificial external field that biases the system towards twophase configurations. The Gibbs free energy difference is then determined from the average force that the field exert on the system. In addition, the method gives information about the interface between the phases. 
Date:  Tue, 05.11.2013 
Time:  12:30 
Duration:  60 min 
Location:  Univ. of Vienna, Faculty of Physics, Boltzmanngasse 5, 5th floor, Erwin Schrödinger Lecture Hall 
Contact:  Albert Georg Passegger, Peter Poier  www.univie.ac.at/lunchseminar 
Quantum dynamical semigroups and their generators 
Speaker:  Bernhard Baumgartner (Univ.Wien) 
Abstract:  im Rahmen des Seminars für Mathematische Physik 
Date:  Tue, 05.11.2013 
Time:  14:15 
Duration:  60 min 
Location:  Fakultät für Physik, ErwinSchrödingerHörsaal, Boltzmanngasse 5, 5. Stock 
Contact:  J. Yngvason 
Initial stages of the growth of iron oxides on Ru(0001) 
Speaker:  Dr. Juan de la Figuera (Instituto de Química Física Rocasolano, Madrid/Spain) 
Abstract:  Magnetite is the most strongly magnetized material found in nature. A revival of interest in magnetite for spintronic applications has been spurred by its multiferroic and halfmetal character, together with its high Curie temperature. Magnetite has been grown on several metal subsrates substrates, such as Pt(111) or Ru(0001). In the first stage, a FeO wetting layer is grown, and only on a second stage magnetite islands nucleate. In this work we present our observations of the growth of iron oxide on Ru by oxygen assisted MBE [14], by a combination of traditional surface science techniques (STM, XPS, LEED) together with lowenergy electronbased microscopies (low energy electron microscopy, spinpolarized lowenergy electron microscopy and photoemission electron microscopy). In the latter case the surface morphology can be followed in real time during the growth. We determine that nan 
Date:  Tue, 05.11.2013 
Time:  16:00 
Location:  Technische Universität Wien, Institut für Angewandte Physik, Seminarraum 134A, Turm B (gelbe Leitfarbe), 5. OG, 1040 Wien, Wiedner Hauptstraße 810 
Contact:  Univ.Prof. Dr. Ulrike Diebold 
New moves in spin choreography: quantum control of atomic qubits and qudits 
Speaker:  Poul JESSEN (Center for Quantum Information and Control (CQuIC), College of Optical Sciences, University of Arizona) 
Abstract:  The standard paradigm for Quantum Information Science involves a collection of qubits, whereas the physical systems considered as building blocks for a quantum processor or simulator often have more than two accessible levels. To take advantage of these higherdimensional Hilbert spaces (qudits), it is necessary to develop a toolbox for quantum control similar to what already exists for qubits. Over the past several years we have used the 16dimensional ground hyperfine manifold of individual Cs atoms as a testbed for such work. Driving the atoms with a combination of phase modulated rf and µw magnetic fields, we use numerical optimization techniques to design control waveforms (rf and µw phases as function of time) that accomplish a wide range of control tasks, from quantum statetostate maps to full unitary transformations, with average fidelities that vary from >99% for the former to ~97% for the latter. Restricting ourselves to qubits encoded in the ground manifold, the tools of inhomogeneous control can applied to the problem of resonance addressing and control of atoms in optical lattices, allowing us to target arbitrary singlequbit gates on desired sites or perform independent gates in parallel across adjacent sites. Other applications of quantum control pursued by our group include an improved atomlight interface and spin squeezing, and an unconventional approach to quantum state and process tomography. 
Date:  Thu, 07.11.2013 
Time:  10:30 
Location:  TU Wien Atominstitut, Hörsaal, Stadionallee 2, 1020 Wien 
Contact:  Arno Rauschenbeutel 
Critical SelfGravitating Wave Maps 
Speaker:  Nishanth Gudapati (AEI Potsdam) 
Abstract:  im Rahmen des Literaturseminars für Gravitation 
Date:  Thu, 07.11.2013 
Time:  14:15 
Duration:  60 min 
Location:  Arbeitsgruppe: Gravitation, Währinger Strasse 17, Seminarraum A, 2. Stock 
Contact:  H. Rumpf 
Irreversible Quantum Dynamics 
Speaker:  Bernhard Baumgartner (Univ. Wien) 
Abstract:  im Rahmen der gemeinsam veranstalteten Seminare "Komplexe Stochastische Systeme" (Univ. Wien) und "Analyse Komplexer Systeme" (Med.Univ.Wien) 
Date:  Fri, 08.11.2013 
Time:  14:15 
Duration:  90 min 
Location:  Fakultät für Physik, ErwinSchrödingerHörsaal, Boltzmanngasse 5, 5. Stock 
Contact:  H. Hüffel, Stefan Thurner 
Quantum crystals of photons and atoms 
Speaker:  Giovanna MORIGI (FR Physik, Universität des Saarlandes) 
Abstract:  In this talk I will discuss the theoretical description of selforganization of atoms in the field of a highfinesse optical resonator. I will first focus on the semiclassical dynamics, when the atoms are confined inside a standingwave highfinesse resonator. The atoms are cooled by scattering processes in which the photons of a transverse laser are coherently scattered into the cavity mode. A FokkerPlanck equation for the atomic centerofmass variables is derived which allows one to determine the equations of motion in the semiclassical limit for any value of the intensity of the laser field. Its prediction are extracted for the dynamics when the resonator is essentially in the vacuum state and the atoms are cooled by scattering photons into the cavity mode, which then decays. Its predictions for the stationary atomic distribution are compared with the ones of the FokkerPlanck equation by Domokos et al. [J. Phys. B 34 187 (2001)], which has been derived under different assumptions.
I will then consider ultracold bosonic atoms in another setup. In detail, the atoms are confined by an optical lattice inside an optical resonator and interact with a cavity mode whose wavelength is incommensurate with the spatial periodicity of the confining potential. The intracavity photon number can be significantly different from zero when the atoms are driven by a transverse laser whose intensity exceeds a threshold value and whose frequency is suitably detuned from the cavity and the atomic transition frequency. In this parameter regime the atoms form clusters in which they emit in phase into the cavity. The clusters are phase locked, thereby maximizing the intracavity photon number. These predictions are based on a BoseHubbard model, whose derivation is reported here in detail. The BoseHubbard Hamiltonian has coefficients which are due to the cavity field and depend on the atomic density at all lattice sites. The corresponding phase diagram is evaluated using quantum Monte Carlo simulations in one dimension and meanfield calculations in two dimensions. Where the intracavity photon number is large, the ground state of the atomic gas lacks superfluidity and possesses finite compressibility, typical of a Bose glass.

Date:  Fri, 08.11.2013 
Time:  15:30 
Location:  TU Wien Atominstitut, Hörsaal, Stadionallee 2, 1020 Wien 
Contact:  Jörg Schmiedmayer 
