Collective atomic recoil lasing and superradiant Rayleigh scattering in a high-Q ring cavity

Cold atoms in optical high-Q cavities are an ideal model system for long-range interacting particle. The position of two arbitrary atoms is, independent on their distance, coupled by the back-scattering of photons within the cavity. This mutual coupling can lead to collective instability and self-organization of a cloud of cold atoms interacting with the cavity fields. This phenomenon (CARL, i.e. Collective Atomic Recoil Lasing) has been discussed theoretically for years, but was observed only recently in our lab. The CARL-effect is closely linked to superradiant Rayleigh scattering, which has been intensely studied with Bose-Einstein condensates in free space. By adding a resonator the coherence time of the system, in which the instability occurs, can be strongly enhanced. This enables us to observe cavity-enhanced superradiance with both Bose-Einstein condensates and thermal clouds and allows us to close the discussion about the role of quantum statistics in superradiant scattering.