
Calendar of Physics Talks Vienna
SpinQubits Coupled to Electric Fields and Photons in Microwave Cavities 
Speaker:  Prof. Daniel Loss (Department of Physics, University of Basel) 
Abstract:  Over the last decade, the spin of electrons in semiconductor nanostructures has been intensively studied in relation to spinbased quantum computing schemes [1,2]. Attaining
an almost full control over the spin of individual electrons in quantum dots opens the possibility to study singlespin dynamics in a solid state environment in the presence of relaxation and decoherence. Although quantum dots have been most successfully used until now to demonstrate spin coherence and usability for quantum computing [2] novel quantum systems have emerged in recent years, providing a number of new ways to implement scalable solid state qubits, especially using electric fields instead of magnetic fields to manipulate the spins. Among such systems are the quantum dots formed inside semiconductor nanowires [3], singlewall carbon nanotubes or the collective spin states of molecular magnets such as Cu3triangles [4]. These systems are distinguished by a sizable coupling strength between electric fields and spin, which emerges from spin orbit interaction in nanostructures or from electric dipole moments associated with chiral spin textures. Such spinelectric couplings are also of central importance in the fields of spintronics and multiferroics which aim at controlling spinmagnetism via electric fields. This new mechanism also opens the door of coupling spin to quantized photon fields of microwave cavities, and to form hybrid systems between qubits of different nature. In my talk, I will present the underlying theoretical concepts, and sketch the derivation of the relevant effective Hamiltonians describing these spinelectric effects. If time permits, I will also discuss an exact solution recently found [5] for the Dicke model describing the coupling between a photon and many spins with inhomogeneous Zeeman splittings.
[1] D. Loss and D. P. DiVincenzo, Phys. Rev. A 57, 120 (1998).
[2] R. Hanson, L. P. Kouwenhoven, J. R. Petta, S. Tarucha, and L. M. K. Vandersypen, Rev.
Mod. Phys. 79, 1217 (2007).
[3] M. Trif, V. N. Golovach, and D. Loss, Phys. Rev. B 75, 085307 (2007).
[4] M. Trif, F. Troiani, D. Stepanenko, and D. Loss, Phys. Rev. Lett. 101, 217201 (2008).
[5] O. Tsyplyatyev and D. Loss, arXiv:0811.2386.

Date:  Mon, 23.03.2009 
Time:  17:30 
Duration:  60 min 
Location:  Hörsaal des Atominstituts, Stadionallee 2, 1020 Wien 
Contact:  Prof. Jörg Schmiedmayer 
Vienna Theory Lunch Club  Center Vortices in Lattice QCD 
Speaker:  Roman Höllwieser (VUT) 
Abstract:  A basic introduction to Lattice QCD and the center vortex model of quark confinement will be presented. Quantum Chromodynamics (QCD) is a theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons making up hadrons (such as the proton, neutron or pion). Lattice QCD (LQCD) is the study of the SU(3) Yang–Mills theory of colorcharged fermions (the quarks), in terms of quantum field theory on a four dimensional spacetime lattice. It is the main tool for probing QCD in the nonperturbative regime, where QCD predicts quark confinement, which means that the force between quarks does not diminish as they are separated. The center vortex model has been proposed as an explanation of confinement in nonAbelian gauge theories. Center vortices, quantized magnetic fluxlines, compress the gluonic flux into tubes and cause a linearly rising potential at large separations. Here, this model will be formulated in SU(2) lattice gauge theory.
Overview lunch club 
Date:  Tue, 24.03.2009 
Time:  12:30 
Duration:  60 min 
Location:  TU Vienna, Inst. f. Theoretical Physics, Freihaus, Wiedner Hauptstr. 810, 10. OG, SEM136 
Contact:  Max Attems, Daniel Grumiller, Beatrix Hiesmayr 
Finite family symmetry groups 
Speaker:  Patrick Ludl (Univ. Wien) (Fakultät für Physik) 
Abstract:  im Rahmen des Teilchenphysikseminars 
Date:  Tue, 24.03.2009 
Time:  16:15 
Duration:  60 min 
Location:  Erwin SchrödingerHörsaal, Boltzmanngasse 5, 5. Stock 
Contact:  W. Grimus, H. Neufeld 
Constructing renormalizable models for gauge fields in noncommutative space 
Speaker:  Daniel Blaschke (Institut f. Theoretische Physik, TU Wien) 
Abstract:  In trying to formulate a quantum field theory on noncommutative spacetime, e.g. by employing the socalled GroenewoldMoyal star product, one inevitably has to deal with the infamous UV/IR mixing problem: New kinds of nonlocal IR divergences prevent the model from being renormalizable. In fact, so far only some modified scalar field theories on Euclidean noncommutative spaces have been found to be renormalizable by successfully circumventing problems due to UV/IR mixing. In this talk I give an introduction to this field of research and present promising candidates for renormalizable noncommutative gauge theories. 
Date:  Wed, 25.03.2009 
Time:  16:15 
Location:  ESI Boltzmann lecture hall 
Contact:  Raimar Wulkenhaar, Daniel Blaschke 
Holographic renormalization 
Speaker:  Daniel Grumiller (VUT) 
Abstract:  An introduction is provided to holographic renormalization. The following questions will be addressed: What is holographic renormalization? Why is it needed, particularly in AdS/CFT? How is it implemented technically? 
Date:  Thu, 26.03.2009 
Time:  14:15 
Duration:  90 min 
Location:  Vienna University of Technology, SEM 136 (10th floor, yellow sector, Freihaus) 
Contact:  Daniel Grumiller, Anton Rebhan 
Hawking radiation, Unruh effect and moving mirrors 
Speaker:  Alexander RETZKER (Imperial College, London) 
Abstract:  In this talk I will review recent suggestions for measuring Hawking like effects in the lab.
In the first part the basic ideas behind the analogy will be explained and a short review of the experimental systems which can serve as candidates to measure these effect. In the second part of the talk the experimental challenges of measuring the Unruh effect in a BEC will be reviewed.

Date:  Fri, 27.03.2009 
Time:  15:15 
Location:  TU WienAtominstitut, Seminarraum, Stadionallee 2, 1020 Wien 
Contact:  Prof. H. Schmiedmayer 
