Sympathetic cooling and collisional properties of a Rb-Cs mixture

We report on measurements of the collisional properties of a mixture of Cs-133 and Rb-87 atoms in a magnetic trap at mu K temperatures. By selectively evaporating the Rb atoms using a radio-frequency field, we achieved sympathetic cooling of Cs down to a few mu K. The interspecies collisional cross section was determined through rethermalization measurements, leading to good agreement with a theoretical prediction of 595a(0) for the triplet s-wave scattering length for Rb in the parallel to F=2,m(F)=2 > and Cs in the parallel to F=4,m(F)=4 > magnetic states. We briefly speculate on the prospects for reaching the Bose-Einstein condensation of Cs inside a magnetic trap through sympathetic cooling.