Photoassociative frequency shift in a quantum degenerate gas

A light-induced frequency shift is observed in single-photon photoassociative spectra of magnetically trapped, quantum degenerate ⁷Li. The shift is a manifestation of the coupling between the threshold continuum scattering states and discrete bound levels in the excited-state molecular potential induced by the photoassociation laser. The frequency shift is observed to be linear in the laser intensity with a measured proportionality constant that is in good agreement with theoretical predictions. This phenomenon has important implications for a scheme to alter the interactions between atoms in a Bose-Einstein condensate using photoassociation resonances.