Overlapping Bose-Einstein condensates of Na 23 and Cs 133

We report on the creation of dual-species Bose-Einstein condensates (BECs) of Na23 atoms and Cs133 atoms. We demonstrate sympathetic cooling of Cs with Na in a magnetic quadrupole trap and a crossed optical dipole trap, leading to Na BECs with 8(1)×105 atoms and Cs BECs with 3.5(1)×104 atoms. Investigating cross thermalization and lifetimes of the mixture, we find that the Na and Cs BECs are miscible and overlapping, interacting with a moderate interspecies scattering length of 18(4)a0 at 23 G and 29(4)a0 at 894 G and coexisting for tens of seconds. Overlapping condensates of Na and Cs offer possibilities for many-body physics with ultracold bosonic mixtures and constitute an ideal starting point for the creation of ultracold ensembles of NaCs ground-state molecules.