Theory of collective Raman scattering from a Bose-Einstein condensate

A quantum theory describing the experimentally observed superradiant Raman scattering from a diluted Bose-Einstein condesate driven by a single off-resonant laser beam was discussed. The theory shows Raman amplification of matter wave due to collective atomic recoil from 3-levels atoms in λ-configuration. A pure two-level system was realized between atoms with different internal states and different momentum, when atoms were initially in one of the two lower states and entangled atom-photon pairs were generated. It was found that when the atoms were initially prepared in both the lower internal states, a friction of atoms recoiling in the backward direction can be generated.