Sympathetic Cooling with Two Atomic Species in an Optical Trap

Abstract

We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO${}_2$ laser and study the exchange of thermal energy between the gases. The cesium gas, which is optically cooled to $20\hat{I}¼$K, efficiently decreases the temperature of the lithium gas through sympathetic cooling. The measured cross section for thermalizing ${}^{133}$Cs-${}^7$Li collisions is $8\times 10^{-12}$ cm${}^2$, for both species in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation).

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