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Conference on Lasers and Electro-Optics

Mixtures of lithium and cesium in a quasi-electrostatic trap

H. Engler, Marcel Carto Constantin Mudrich, Tino Weber, Wendel Wohlleben, Rudolf Grimm, M. Weidenmüller

Published Aug 29, 2005• 0 citations
Publisher

Abstract

Summary form only given. A quasi-electrostatic trap (QUEST) realized with a CO/sub 2/ laser relies on the electrostatic polarizability of the trapped particles and therefore represents a universal storage device for ultracold particles. All intriguing application of the QUEST is the simultaneous storage of different atomic species. Elastic and inelastic ground-state interactions can be investigated, one species may act as an agent to sympathetically cool the other species, and the formation and storage of cold ground-state molecules becomes possible in the same trapping volume. Our experiments start with a two-species magneto-optical trap for lithium and cesium.

DOI
10.1109/iqec.2000.907980

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Summary form only given. A quasi-electrostatic trap (QUEST) realized with a CO/sub 2/ laser relies on the electrostatic polarizability of the trapped particles and therefore represents a universal storage device for ultracold particles. All intriguing application of the QUEST is the simultaneous storage of different atomic species. Elastic and inelastic ground-state interactions can be investigated, one species may act as an agent to sympathetically cool the other species, and the formation and storage of cold ground-state molecules becomes possible in the same trapping volume. Our experiments start with a two-species magneto-optical trap for lithium and cesium.
A cold atomic gas formed by two different species represents an intriguing system for a deeper understanding of atom-atom interactions at ultralow temperatures. We present experiments on a mixture of atomic lithium and cesium which are of particular interest regarding the formation of heteronuclear molecules on the one hand, and the prospects for sympathetic cooling of atomic gases through mutual thermalization on the other hand. A first series of experiments on interaction in presence of a near-resonant light field is performed in a two-species magneto-optical trap. The collisional properties of the lithium-cesium mixture are investigated through detailed analysis of trap-loss processes induced by the trap light. Photoassociation in an additional near-resonant laser field yields high-resolution spectra of the excited Cs_2 dimers, but shows no unambiguous indication of LiCs molecule formation. A second series of experiments on pure ground-state collisional properties utilizes an optical dipole trap formed by light that is detuned extremely far below atomic resonance (quasi-electrostatic trap). Storage times of many minutes are achieved in a particularly simple and versatile setup for both atomic species. Cooling of cesium through evaporation and thermalization by elastic collisions is observed. The evolution of temperature and particle number is compared with model simulations of evaporative cooling. Direct laser cooling of trapped cesium in the absolute energetic ground state is demonstrated. Homonuclear spin-changing collisions of ground-state cesium and lithium atoms are analyzed, and first evidence for pure ground-state collisions between atoms of different species is found. Based on the current achievements, prospects for future experiments are discussed. (orig.)
We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO2{\mathrm{CO}}_{2}CO2​ 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).
We present first indications of sympathetic cooling between two neutral trapped atomic species. Lithium and cesium atoms are simultaneously stored in an optical dipole trap formed by the focus of a CO2 laser, and allowed to interact for a given period of time. The temperature of the lithium gas is found to decrease when in thermal contact with cold cesium. The timescale of thermalization yields an estimate for the Li-Cs cross-section. Mixtures of atomic gases enrich the field of physics with ultracold gases by making many interesting phenomena available for experimental study. A prime example is the exchange of thermal energy between different components in the mixture. This cross-thermalization can be used for determining inter-species collision cross-sections, and, more importantly, for sympathetic cooling. The process of sympathetic cooling, where the gas of interest is cooled through thermalization with a coolant gas, is especially advantageous if the cooled gas (Li in our case) is hard to cool by other methods, while the coolant gas (Cs) allows for efficient laser cooling. The Li can only be
We present first indications of sympathetic cooling between two neutral, optically trapped atomic species. Lithium and cesium atoms are simultaneously stored in an optical dipole trap formed by the focus of a CO2_22​ laser, and allowed to interact for a given period of time. The temperature of the lithium gas is found to decrease when in thermal contact with cold cesium. The timescale of thermalization yields an estimate for the Li-Cs cross-section.
Storing and cooling simultaneously lithium and sodium atoms in a two-species magneto-optical trap, rate coefficients for collisions between these two atomic species were determined. The experiments were performed at different trap depths, thus for Li atoms the trap losses due to finestructure changing collisions could be distinguished from losses due to radiative escape. The rate coefficient for collisions between sodium and lithium atoms shows also a step when increasing the trap depth. The formation of cold heteronuclear molecules is claimed.
We present a machine built for experiments with ultracold mixtures of strontium and lithium atoms. The machine includes a science vacuum chamber and the relevant laser systems for cooling and trapping the atoms. With this machine, we realize a D2-line compressed magneto-optical trap (MOT) for 6{^6}6Li and a narrow-linewidth 689-nm MOT for 84^{84}84Sr, obtaining ~10910^9109 6{^6}6Li atoms at 700 μμμK and ~10710^7107 84^{84}84Sr atoms at 1.8 μμμK. Such a dual-species MOT provides an ideal starting point for realizing double degenerate mixtures of 6^66Li and Sr atoms.