Crossed-beam optically degenerate wave mixing with bosonic quantum gases

Highly efficient, optical-degenerate wave-mixing involving bosonic quantum gas is studied using a crossed-beam geometry. We show a very large enhancement due to nonlinear gain from a matter-optical wave-mixing process involving four photons and two matter-wave excitations. Under suitable conditions with a red-detuned pump field this optically degenerate, four-photon process can be stronger than the traditional two-photon inelastic light-scattering mechanism, leading to strong nonlinear growth of the observed matter-wave scattering. This optically degenerate four-wave mixing is independent of other enhancements arising from bosonic stimulations. More importantly, this highly efficient, backward degenerate wave generation and growth process does not have a correspondence in thermal gases in nonlinear optics.