Vendredi 13 janvier 2006 à 14h30
During this thesis we have studied two distinct physical situations in which quantized vortices appear in atomic Bose-Einstein condensates. In the first case, when the dimensionality of the BEC is reduced by loading it into a 1-dimensional optical lattice, vortices appear as thermal excitations above the ground state. In the second case, when a 3-dimensional BEC is set into fast rotation, the ground state of the system contains vortices. In an optical lattice an array of independent 2-dimensional Bose-Einstein condensates is produced from an initially 3-dimensional cloud. The number of 2D BECs in this array can be controlled by superimposing a magnetic field gradient along the axis of the lattice and then selectively evaporating the sites. When producing a small number of sites and letting them interfere, dislocations in the interference pattern were observed, which must be due to nontrivial phase defects, as for example free vortices. Such vortices and vortex-antivortex pairs play an important role in the superfluid to normal phase transition in a 2-dimensional gas, the Kosterlitz-Thouless transition. With 3-dimensional condensates the limit of fast rotation is studied in a hybrid potential containing a small quartic term. In this trap rotation frequencies larger than the harmonic trapping frequency can be reached.
These experiments are a first step to a possible observation of strongly correlated states close to the regime of the fractional quantum Hall effect.
RECRUTEMENT ACCES DIRECT
Le département de physique
Le Laboratoire de Physique de l’ENS 