Observation of Feshbach resonances between ultracold Na and Rb atoms

Absolute ground-state $^{23}$Na$^{87}$Rb molecule has a large electric dipole moment of 3.3 Debye and its two body exchange chemical reaction is energetically forbidden at ultracold temperatures. It is thus a nice candidate for studying quantum gases with dipolar interactions. We have built an experiment setup to investigate ultracold collisions between Na and Rb atoms as a first step toward the production of ground state molecular samples. Ultracold mixtures are first obtained by evaporative cooling of Rb and sympathetic cooling of Na. They are then transferred to a crossed dipole trap and prepared in different spin combinations for Feshbach resonance study. Several resonances below 1000 G are observed with both atoms prepared in either $\left|F = 1, m_F = 1\right\rangle$ or $\left|F = 1, m_F = -1\right\rangle$ hyperfine states. Most of them are within 30 G of predicted values$^{\S}$ based on potentials obtained by high quality molecular spectroscopy studies. This work is supported by RGC Hong Kong. \\\noindent ${\S}$ E. Tiemann, private communications