Berlin 2005 – wissenschaftliches Programm
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A: Atomphysik
A 13: Poster HU 2
A 13.59: Poster
Dienstag, 8. März 2005, 08:30–18:30, Poster HU
Phase fluctuations in a two-dimensional, harmonically trapped, dilute Bose gas at finite temperatures — •Christopher Gies1 and D. A. W. Hutchinson2 — 1Institut für Theoretische Physik, Universität Bremen — 2Department of Physics, University of Otago, Dunedin, New Zealand
Experimental realization of Bose-Einstein condensation (BEC) in lower dimensions is a very recent achievement and holds yet unexplored features. We present a fully quantum mechanical Hartree-Fock-Bogoliubov treatment of the dilute Bose gas which is spatially confined to two dimensions, following the methods described in [C. Gies et al., PRA 70, 043606 (2004)]. We investigate the possibility of BEC at finite temperatures and focus on the influence of long wavelength phase fluctuations. These lead to a transition from the true BEC to a quasicondensate at sufficiently high temperatures, where the phase coherence remains only over a finite length smaller than the system size. This regime and its relation to the Kosterlitz-Thouless phase, where global phase coherence is destroyed by vortex/antivortex pairs, is discussed.
Our results include low-lying excitation frequencies, first order coherence function and momentum spectrum of the condensate in the temperature regime below the critical temperature. The momentum spectrum, from which the coherence function can be derived, could be measured via Bragg spectroscopy and is, thus, of importance for experimental verification. The low-lying excitation spectrum holds a peculiarity due to the symmetry of the two-dimensional contact interaction potential, which we confirm numerically.