Observation of Feshbach resonances between ultracold Na and Rb atoms

We have successfully prepared an optically trapped ultracold mixture of $^{23}$Na and $^{87}$Rb atoms and studied their interspecies Feshbach resonances. Using different spin combinations, 9 $s$-wave and $p$-wave resonances are identified by observing the high inelastic losses and temperature increases for both species near resonant fields. The two $s$-wave resonances 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 and are used to refine the ground state interspecies collision properties between $^{23}$Na and $^{87}$Rb. This work opens up the prospect for ground-state bosonic NaRb molecules which are chemically stable and can provide strong dipolar interactions.