RF two-photon assosiation of p-wave Feshbach molecules in the ultracold ⁶Li system

Significant progress has been made with s-wave Feshbach resonances, including studies of the smooth crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid. The anisotropic p-wave interaction also offers various phase transitions, such as from a px superfluid to a px + ipy superfluid, as well as the topological quantum phase transition from a gapped to a gapless px + ipy superfluid. For the BEC side of the study, the molecule needs to be created but adiabatic sweeps like s-wave resonances do not necessarily produce p-wave Feshbach molecules efficiently due to three body losses. Recently, we have observed radio frequency (RF) degenerated two-photon association in a ultracold 6Li system, which offers another way to create the molecules. First. we performed RF spectroscopy of a spin mixture of two hyperfine ground states at different magnetic field and there were two frequencies that induced losses. Then we find that one corresponds to usual spin-flip association and the other corresponds to unusual spin-flip degenerate two-photon association. Second, we measured time evolutions of these processes and extracted molecule creation rates. It is proportional to square of RF intensity, which is strong evidence of two-photon process. We also extracted the loss rates and evaluated this method.