Grey-molasses cooling of an optically trapped Fermi gas

Robust sub-Doppler cooling has recently been demonstrated at the D1 (nS$_{1/2}$ to nP$_{1/2}$) transition of potassium [1-3] and lithium [4], atoms that are challenging to cool on the D2 cycling transition. Two mechanisms are at work: first, Sisyphus cooling in the standing-wave dipole potential, at least partially due to polarization gradients [1]; second, velocity-selective coherent population trapping (VSCPT) in a superposition of the two hyperfine ground states [2-4]. We extend this technique to the cooling of dense clouds in optical traps. Since the VSCPT dark state relies only on ground-state coherences, it is insensitive to optical shifts from far-detuned optical traps. We also observe that the molasses has sufficient cooling power to withstand light scattering on the 4S-5P transition. Together these observations indicate that D1 cooling is a promising approach to fluorescent imaging of single fermions in an optical lattice. \\[4pt] [1] D. Rio Fernandes et al., EPL, 100 63001 (2012).\\[0pt] [2] D. Nath et al., PRA, 88 053407 (2013).\\[0pt] [3] G. Salomon et al., EPL, 104 63002 (2013).\\[0pt] [4] A. T. Grier et al., PRA 87 063411 (2013).