Calendar of Physics Talks Vienna

Using Matter-waves and optical disorder to study coherent transport and Anderson Localisation
Speaker:Philippe Bouyer (Laboratoire Charles Fabry de l’Institut d’Optique, France)
Abstract:Disorder has long proven to be a crucial ingredient to understand coherent transport properties. The most prominent example is the weak localization phenomenon in mesoscopic physics, which has been studied extensively for electrons and for classical waves. Weak localization arises from interference between multiply scattered waves in a random medium. This interference survives the configuration average over many realizations of disorder and reduces the conductivity that enters the Drude model for electron transport and the diffusion constant of classical radiative transport theory. Disorder can even induce a metalinsulator transition, known as the strong (or Anderson) localization transition. In 1958, P.W. Anderson predicted the exponential localization1 of electronic wave functions in disordered crystals and the resulting absence of diffusion. It has been realized later that Anderson localization (AL) is ubiquitous in wave physics2 as it originates from the interference between multiple scattering paths, and this has prompted an intense activity. Experimentally, localization has been reported in light waves , microwaves, sound waves,and electron gases.Recent progress in ultracold atomic systems has triggered a renewed interest in quantum disorderedsystems where several effects such as localization. Ultracold atoms in optical and magnetic potentialsprovide an isolated, defectless and highly controllable system and thus offer an exciting (new) laboratory inwhich quantummany-body phenomena at the border between atomic physics and condensedmatter physicscan be addressed. We present here the observation of Anderson localization3 of a Bose-Einstein condensate (BEC) released into a one-dimensional waveguide in the presence of a controlled disorder created by laserspeckle. We also show that, in our one-dimensional speckle potentials whose noise spectrum has a highspatial frequency cut-off, exponential localization occurs only when the de Broglie wavelengths of the atoms in the expanding BEC are larger than an effective mobility edge corresponding to that cut-off. In theopposite case, we find that the density profiles decay algebraically4. 1Anderson, P.W., Phys. Rev. 109, 1492-1505 (1958) 2Van Tiggelen, B. , In Wave diffusion in complex media, edited by J.P. Fouque, (Kluwer, Dordrecht, 1999). 3Billy, J., el al., to appear in Nature. 4Sanchez-Palencia, L., , et al., Phys. Rev. Lett. 98, 210401 (2007).
Date: Mon, 20.04.2009
Time: 17:30
Duration: 60 min
Location:Hörsaal des Atominstituts, Stadionallee 2, 1020 Wien
Contact:Prof. Markus Arndt, Universität Wien

Vienna Theory Lunch Club - Massive gravity
Speaker:Olaf Hohm (Groningen University)
Abstract:In this talk I introduce a recent proposal for a theory of massive gravity in three dimensions. First, I review the consistency problems for massive spin-2 theories in generic dimensions. Then, I explain special features in three dimensions such as the possibility of gauge invariant mass terms and, in particular, topologically massive gravity. Using these special three-dimensional features I explain how a non-linear "covariantisation" of massive gravity can be introduced in D=3 via higher-derivative couplings.
Overview lunch club
Date: Tue, 21.04.2009
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

Rotierende Bose Gase: Grundlagen
Speaker:Clemens Moser (Wien) (Fakultät für Physik)
Abstract:im Rahmen des Seminars für Mathematische Physik
Date: Tue, 21.04.2009
Time: 14:30
Duration: 60 min
Location:Erwin Schrödinger-Hörsaal (ehem. Großer Seminarraum), Boltzmanngasse 5, 5. Stock
Contact:J. Yngvason

Analyticity and Dispersion Relation Constraints on the Electromagnetic Formfactor of the Pion
Speaker:B. Ananthanarayan (Centre for High Energy Physics, Indian Inst. of Science) (Fakultät für Physik)
Abstract:im Rahmen des Teilchenphysikseminars
Date: Tue, 21.04.2009
Time: 16:15
Duration: 60 min
Location:Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:G. Ecker, H. Neufeld