Observation of Feshbach resonances between ultracold Na and Rb atoms

We have successfully prepared an optically trapped ultracold mixture of Na-23 and Rb-87 atoms and studied their interspecies Feshbach resonances. Using two different spin combinations, several s- and p-wave resonances are identified by observing high inelastic losses and temperature increases for both species near resonant magnetic field values. The two s-wave resonances observed below 500 G between atoms in their lowest-energy levels are possible candidates for Feshbach molecule association. Our results are well characterized by a coupled-channel model which also refines the ground-state interaction potentials between Na-23 and Rb-87. This work opens up the prospect for preparing ultracold ensembles of ground-state bosonic NaRb molecules which are chemically stable and can provide strong dipolar interactions.