Jeudi 20 mars 2003
I will first give a general introduction to the subject of cold gases and describe the first generation of studies, starting with the discovery of Bose-Einstein condensation (BEC) in alkali atom clouds at JILA and MIT in 1995. It will be emphasized that first experiments with trapped Bose-condensed gases have revealed profound collective (condensed matter) behavior of these extremely dilute systems, originating from the dominant role of interparticle< interaction. The next step will the description of phase coherence studies in trapped condensates. Aside from fundamental aspects, these studies are important for future applications, such as atom lasers and atom interferometry. I will discuss to which extent the phase decoherence in elongated condensates is related to the physics of one-dimensional (1D) Bose gases. Introducing the notion of a quasicondensate, or condensate with fluctuating phase, I will analyze the results of recent experiments at Hannover and at Orsay.
The second half of the talk will be dedicated to quantum degenerate regimes in 1D trapped Bose gases, which are created by (tightly) confining the motion of particles in two directions to zero point oscillations. Emphasizing the presence of two physically distinct regimes - the quasicondensate regime and the strongly interacting Tonks regime of "fermionization", I will discuss how correlation properties of the gas manifest themselves in the rates of intrinsic inelastic processes, such as 3-body recombination. It will be shown that fermionization enhances the stability of the gas and makes it possible to achieve large densities. In conclusion, I will discuss current experiments and prospects on achieving fermionization in Bose gases.