Friday, April 26, 2013

1304.6971 (Andrew T. Grier et al.)

Λ-enhanced Sub-Doppler Cooling of Lithium Atoms in D1 Gray

Andrew T. Grier, Igor Ferrier-Barbut, Benno S. Rem, Marion Delehaye, Lev Khaykovich, Frédéric Chevy, Christophe Salomon
Following the bichromatic sub-Doppler cooling scheme on the D1-line of 40K recently demonstrated in (Fernandes et al. 2012), we introduce a similar technique for 7Li atoms and obtain temperatures of 60 uK while capturing all of the 5x10^8 atoms present from the previous stage. We investigate the influence of the detuning between the the two cooling frequencies and observe a threefold decrease of the temperature when the Raman condition is fulfilled. We interpret this effect as arising from extra cooling due to long-lived coherences between hyperfine states. Solving the optical Bloch equations for a simplified, \Lambda-type three-level system we identify the presence of an efficient cooling force near the Raman condition. After transfer into a quadrupole magnetic trap, we measure a phase space density of ~10^-5. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.
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