Laboratoire de Physique Théorique
Toulouse - UMR 5152

Weak localization represents a universal wave phenomenon that plays an important role in mesoscopic transport physics in the presence of disorder or chaos. Its most characteristic signature is the peak of coherent backscattering, which corresponds to an enhancement of the backscattered intensity of a wave in the direction of retro-reflection. This coherent backscattering peak arises due to constructive interference between reflected paths and their time-reversed counterparts and has recently been observed with Bose-Einstein condensates. In my talk, I shall discuss the results of our theoretical study on weak localization of interacting bosonic atom-laser beams that coherently propagate through two-dimensional disorder potentials or chaotic billiard geometries. Our approach is based on the Gross-Pitaevskii equation which is numerically integrated in order to obtain stationary scattering states of the bosonic beam, and which represents the starting point for an analytical description of the scattering process in terms of nonlinear diagrammatic theory. We find that the presence of atom-atom interaction within the condensate gives rise to signatures of weak antilocalization, i.e., to an inversion of the coherent backscattering peak in disordered systems and to a reduction, instead of an enhancement, of the retro-reflection probability in chaotic billiard geometries. Short-path contributions associated, in particular, with self-retraced trajectories are conjectured to be at the origin of this antilocalization phenomenon.