| In general, transport of waves in disordered media cannot fully be described as a simple diffusion process, since wave interference effects lead to a reduction or even complete suppression of the diffusion constant (weak or strong localization) and the appearance of a coherent backscattering peak. In this talk, I present a diagrammatic theory for treating the impact of nonlinearities on coherent backscattering. The theory is applied to describe propagation of weakly interacting Bose-Einstein condensates in disordered potentials, on the one hand, and multiple scattering of light in nonlinear media, on the other one. In particular, the conditions under which nonlinear effects diminish or enhance the height of the coherent backscattering peak are discussed. Finally, I also talk about the possibility to incorporate quantum-mechanical many-particle effects (for example multi-photon scattering processes from strongly driven two-level atoms), which generally lead to decoherence, thereby affecting the disorder-induced localization effects. |
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