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Λ -enhanced sub-Doppler cooling of lithium atoms in D 1 gray molasses

2013; American Physical Society; Volume: 87; Issue: 6 Linguagem: Inglês

10.1103/physreva.87.063411

1538-4446

Andrew T. Grier, Igor Ferrier-Barbut, Benno S. Rem, Marion Delehaye, Lev Khaykovich, Frédéric Chevy, Christophe Salomon,

Quantum Information and Cryptography

Following the bichromatic sub-Doppler cooling scheme on the ${D}_{1}$ line of ${}^{40}$K recently demonstrated in Fernandes et al. [Europhys. Lett. 100, 63001 (2012)], we introduce a similar technique for ${}^{7}$Li atoms and obtain temperatures of $60\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ while capturing all of the $5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ 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 $\ensuremath{\Lambda}$-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 $\ensuremath{\sim}$${10}^{\ensuremath{-}5}$. This laser cooling offers a promising route for fast evaporation of lithium atoms to quantum degeneracy in optical or magnetic traps.