Laboratoire de Physique Théorique
Toulouse - UMR 5152

A gas of immobile two-level atoms at random positions is probably the simplest physical system in which multiple scattering and eventually Anderson localization of light can be studied. This system combines the relative simplicity of a rigorous theoretical description with the feasibility of experiments. However, we have recently established that it does not allow for Anderson localization of light [1]. Localization effects are counteracted by resonant dipole-dipole interactions between nearby atoms. These interactions open a new, nonradiative channel for energy transport that dominates at high atomic densities. This qualitative picture suggests that suppression of dipole-dipole interactions may be a way towards Anderson localization of light in a cloud of cold atoms. Because such a suppression is known to occur in a magnetic field, we now study multiple scattering of light by atoms subject to a strong external field and show that a transition between extended and localized states indeed takes place [2]. The work in progress concerns precise characterization of the discovered localization transition and its classification as an Anderson transition or as a transition of a different type. Indeed, collective atomic phenomena (Dicke sub- and superradiance) as well as dipole-dipole interactions between atoms play important roles at the transition point and may deprive the discovered transition of the universality known for disorder-induced localization-delocalization transitions in simpler systems.

[1] S.E. Skipetrov and I.M. Sokolov, Phys. Rev. Lett. 112, 023905 (2014)

[2] S.E. Skipetrov and I.M. Sokolov, Phys. Rev. Lett. 114, 053902 (2015)