Phase conjugation of trapped Bose-Einstein condensates

We consider a multicomponent atomic Bose-Einstein condensate optically trapped in a far-off resonant dipole trap. Drawing an analogy with the optical situation, we show that this system can be regarded as an matter-wave analog of optical multiwave mixing. We concentrate specifically on condenstates in the hyperfine ground state F=1, in which case a simple analogy with optical four-wave mixing can be established. This opens up the way to realize matter-wave phase conjugation, whereby an atomic beam can be ``time-reversed.‘’ In addition to transfering population between a “central” mode and incident and retroreflecting beams, matter-wave phase conjugation also offers novel diagnostic tools to study the coherence properties of condensates, as well as to measure the relative scattering lengths of hyperfine sublevels.