Hyperfine-changing collisions in an optically trapped gas of ultracold cesium and lithium

Abstract

We present measurements of the rate of hyperfine-state-changing collisions of unpolarized cesium $(^{133}\mathrm{Cs})$ and lithium $(^{7}\mathrm{Li})$ atoms confined in an optical dipole trap in the temperature range between 30 and $130\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$. To infer rate coefficients from trap-loss data, we derive a simple thermodynamic model describing relaxation heating as a consequence of atom loss in a conservative potential. For hyperfine-changing $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{Cs}$ collisions, the experimental results are compared with theoretical predictions and excellent agreement is found. Hyperfine-state-changing collisions in a mixture of lithium and cesium atoms are observed and rate coefficients are inferred for all combinations of hyperfine ground-state asymptotes.