\Lambda-enhanced Sub-Doppler Cooling of Lithium Atoms in D1 Gray Molasses

TL;DR

This paper demonstrates a -enhanced sub-Doppler cooling technique for lithium atoms using D1 gray molasses, achieving ultra-cold temperatures and high atom capture efficiency, with potential for rapid quantum degeneracy preparation.

Contribution

It introduces a -enhanced cooling scheme for lithium, revealing the role of Raman conditions and long-lived coherences in achieving lower temperatures.

Findings

Achieved 60  cooling temperature for 7Li atoms.

Observed a threefold temperature decrease at the Raman condition.

Measured a phase space density of ^{-5} after magnetic trapping.

Abstract

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.