Production efficiency of ultracold Feshbach molecules in bosonic and fermionic systems

We investigate the production efficiency of ultracold molecules in bosonic Rb-85 and fermionic K-40 when the magnetic field is swept across a Feshbach resonance. For adiabatic sweeps of the magnetic field, our novel model shows that the conversion efficiency of both species is solely determined by the phase space density of the atomic cloud, in contrast with a number of theoretical predictions. In the nonadiabatic regime our measurements of the Rb-85 molecule conversion efficiency follow a Landau-Zener model.