Multiple scattering of light in cold atomic clouds in a magnetic field.

Starting from a microscopic theory for atomic scatterers, we describe the scattering of light by a single atom and study the coherent propagation of light in a cold atomic cloud in the presence of a magnetic field B in the mesoscopic regime. Nonpertubative expressions in B are given for the magneto-optical effects and optical anisotropy. We then consider the multiple-scattering regime and address the fate of the coherent-backscattering (CBS) effect. We show that, for atoms with nonzero spin in their ground state, the CBS interference contrast can be increased compared to its value when B=0, a result at variance with classical samples. We validate our theoretical results by a quantitative comparison with experimental data. [ABSTRACT FROM AUTHOR]