Coherent light scattering by cold atoms

Propagation in a random medium is often described by a random walk and a diffusion coefficient. However in the mesoscopic regime, where wave properties cannot be neglected, interferences alter the diffusion process leading in extreme situations to strong (Anderson) localisation. The recent observation of coherent backscattering of light by laser cooled atoms has opened the way to new studies in previously not accessible regimes. Here we present some of the questions addressed by these experiments, allowing for a more complete understanding of the physical processes involved in this quantum mesoscopic regime