Feshbach-molecule formation in a Bose-Fermi mixture

We investigate magnetoassociation of ultracold fermionic Feshbach molecules in a mixture of K-40 and Rb-87 atoms, where we can create (KRb)-K-40-Rb-87 molecules with a conversion efficiency as high as 45%. In the limit of fast magnetic sweeps and small molecule fraction, we find that the time scale of molecule production is accurately predicted by a parameter-free model that uses only the atomic densities, masses, and the known Feshbach resonance parameters. We find that molecule production efficiency saturates for slower magnetic sweeps, at which point the maximum number of Feshbach molecules depends primarily on the atoms' phase-space density. At higher temperatures, our measurements agree with a phenomenological model that successfully describes the formation of bosonic molecules from either Bose or Fermi gases. However, for quantum degenerate atom gas mixtures, we measure significantly fewer molecules than this model predicts. DOI: 10.1103/PhysRevA.87.012703