Creation of heteronuclear Feshbach molecules with $^{85}$Rb and $^{87}$Rb

We will report on the creation of ultracold heteronuclear Feshbach molecules. Heteronuclear molecules in low-lying vibrational states are particularly interesting since they are predicted to exhibit a permanent dipole moment due to the unequal distribution of electrons. Although no significant permanent dipole moment is expected to exist in a $^{85}$Rb -- $^{87}$Rb molecule, our work demonstrates a first step toward the efficient production of ground-state ultracold heteronuclear molecules. Starting with a $^{87}$Rb BEC and a cold thermal gas of $^{85}$Rb, we utilize previously unobserved interspecies Feshbach resonances to create up to 25,000 molecules. The presence of two species with different quantum degeneracy provides a rich system for testing our understanding of the conversion efficiency from atoms to molecules. We can also create a simultaneously Bose-condensed sample of $^{85}$Rb and $^{87}$Rb. The effects of immiscibility in this two-component quantum fluid on the creation of heteronuclear molecules will be discussed.