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arXiv:physics/0111213 · Physical Review Letters

Sympathetic Cooling with Two Atomic Species in an Optical Trap

Marcel Carto Constantin Mudrich, Stephan Kraft, Kilian Singer, Rudolf Grimm, Allard P. Mosk, Matthias Weidemüller

Published Jun 7, 2002• 139 citations
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Abstract

We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a ${\mathrm{CO}}_{2}$ laser and study the exchange of thermal energy between the gases. The optically cooled cesium gas efficiently decreases the temperature of the lithium gas through sympathetic cooling. Equilibrium temperatures down to $25\ensuremath{\mu}\mathrm{K}$ have been reached. The measured cross section for thermalizing ${}^{133}\mathrm{Cs}{\ensuremath{-}}^{7}\mathrm{Li}$ collisions is $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{cm}}^{2}$, for both species unpolarized in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation).

DOI
10.1103/physrevlett.88.253001

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We present measurements of the rate of hyperfine-state-changing collisions of unpolarized cesium (133Cs)(^{133}\mathrm{Cs})(133Cs) and lithium (7Li)(^{7}\mathrm{Li})(7Li) 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.
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