Berlin 2001 – scientific programme

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A: Atomphysik

A 15: Cooling and Trapping IV (joint session A and Q)

A 15.2: Talk

Thursday, April 5, 2001, 16:00–16:15, H104

Sympathetic cooling and evaporation in a mixture of ultracold trapped atoms — •Allard Mosk¹, Marcel Mudrich¹, Stephan Kraft¹, Rudolf Grimm², and Matthias Weidemüller¹ — ¹Max-Planck-Institut für Kernphysik, 69029 Heidelberg, Germany — ²Institut für Experimentalphysik, Universität Innsbruck, Austria

We study thermalization and evaporation in a mixture of ultracold Cs and Li atoms in a quasi-electrostatic trap (QUEST), which confines the atoms in the focus of a 100-W CO₂ laser beam [1]. The QUEST allows us to trap atoms in their hyperfine ground state, for which elastic collisions dominate the kinetics of the gas. The Cs-Li mixture is especially interesting as the temperature of the Cs in our trap can be made very much lower ( ∼ 10 µK) than the temperatures that can be reached in laser cooling of Li (∼ 0.5 mK). Furthermore, the internal thermalization of Li and Cs gases is completely different: The Cs-Cs elastic cross-section is very large at low temperature, while the Li-Li cross-section is three orders of magnitude smaller. The Cs-Li cross-section is a priori unknown. Measurements of the composition of the gas and the temperatures of the components indicate that “sympathetic evaporation” takes place, in which the initially hotter Li atoms cool the Cs gas by evaporating through Cs-Li collisions. Simulations of the experiment support this interpretation, and indicate that the Cs-Li scattering cross-section is large (>10⁴ a₀²).

[1] H. Engler et al, Phys. Rev. A 62, 031402(R) (2000)