A high phase-space density mixture of 87Rb and 133Cs: towards ultracold heteronuclear molecules

We report the production of a high phase-space density mixture of Rb-87 and Cs-133 atoms in a levitated crossed optical dipole trap as the first step towards the creation of ultracold RbCs molecules via magneto-association. We present a simple and robust experimental setup designed for the sympathetic cooling of Cs-133 via interspecies elastic collisions with Rb-87. Working with the |F = 1,m (F) = +1 > and the |3, +3 > states of Rb-87 and Cs-133 respectively, we measure a high interspecies three-body inelastic collision rate similar to 10(-25)-10(-26) cm(6) s(-1) which hinders the sympathetic cooling. Nevertheless by careful tailoring of the evaporation we can produce phase-space densities near quantum degeneracy for both species simultaneously. In addition we report the observation of an interspecies Feshbach resonance at 181.7(5) G and demonstrate the creation of Cs-2 molecules via magneto-association on the 4(g)4 resonance at 19.8 G. These results represent important steps towards the creation of ultracold RbCs molecules in our apparatus.