Sympathetic cooling and collisional properties of a Rb-Cs mixture

Abstract

We report on measurements of the collisional properties of a mixture of ${}^{133}$Cs and ${}^{87}$Rb atoms in a magnetic trap at $\mu \mathrm{K}$ temperatures. By selectively evaporating the Rb atoms using a radio-frequency field, we achieved sympathetic cooling of Cs down to a few $\mu \mathrm{K}$. The inter-species collisional cross-section was determined through rethermalization measurements, leading to an estimate of $a_s=595a_0$ for the s-wave scattering length for Rb in the $|F=2,m_F=2>$ and Cs in the $|F=4,m_F=4>$ magnetic states. We briefly speculate on the prospects for reaching Bose-Einstein condensation of Cs inside a magnetic trap through sympathetic cooling.