Calendar of Physics Talks Vienna

Spin-Qubits 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 spin-based quantum computing schemes [1,2]. Attaining an almost full control over the spin of individual electrons in quantum dots opens the possibility to study single-spin 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], single-wall carbon nanotubes or the collective spin states of molecular magnets such as Cu3-triangles [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 spin-electric couplings are also of central importance in the fields of spintronics and multiferroics which aim at controlling spin-magnetism 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 spin-electric 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 color-charged fermions (the quarks), in terms of quantum field theory on a four dimensional space-time lattice. It is the main tool for probing QCD in the non-perturbative 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 non-Abelian gauge theories. Center vortices, quantized magnetic flux-lines, 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. 8-10, 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 Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:W. Grimus, H. Neufeld

Constructing renormalizable models for gauge fields in non-commutative space
Speaker:Daniel Blaschke (Institut f. Theoretische Physik, TU Wien)
Abstract:In trying to formulate a quantum field theory on non-commutative space-time, e.g. by employing the so-called Groenewold-Moyal star product, one inevitably has to deal with the infamous UV/IR mixing problem: New kinds of non-local IR divergences prevent the model from being renormalizable. In fact, so far only some modified scalar field theories on Euclidean non-commutative 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 non-commutative 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 Wien-Atominstitut, Seminarraum, Stadionallee 2, 1020 Wien
Contact:Prof. H. Schmiedmayer