Cooperative effects in atom field interactions in a Bose-Einstein condensate

Using a semiclassical theory we give a unified approach to a class of coherent atom field interactions in a Bose-Einstein condensate, including superradiant light scattering, coherent amplification of atoms, and coherent light amplification. The populations of the excited states are explicitly taken into account, and the role of the recoil kinetic energies of the atoms with different momenta is discussed. In addition to the known features of superradiant emission, we obtain a shift in the spectrum of the scattered light as a consequence of the atomic recoil. The same theoretical method yields results that are in agreement with the experimental findings for atomic beam amplification, as well as for light amplification. Considering the atomic beam amplification process, we obtain a single outgoing amplified atomic beam. In treating, the coherent light amplification, the unexpectedly small group velocity seen in the experiments is reproduced, and connected to the double A configuration of the levels involved.