Simultaneous sub-Doppler laser cooling of Li6 and Li7 isotopes

Abstract

We report on the simultaneous sub-Doppler laser cooling of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ isotopes using gray molasses operating on their respective ${D}_{1}$ atomic transitions. For $^{7}\mathrm{Li}$ we show that the sub-Doppler cooling can be achieved with two distinct $\mathrm{\ensuremath{\Lambda}}$-type transitions, where the upper level can be either of the two ${2}^{2}\phantom{\rule{0.16em}{0ex}}{P}_{1/2}$ hyperfine states. We obtain temperatures of $\ensuremath{\sim}85\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$, with atom numbers of $\ensuremath{\sim}{10}^{8}$, and phase-space densities in the range of ${10}^{\ensuremath{-}6}\ensuremath{-}{10}^{\ensuremath{-}5}$ for both isotopes. These conditions provide a good starting point for loading the mixture into an optical dipole trap and performing evaporative cooling to quantum degeneracy. Our work provides a valuable simplification for the preparation of ultracold $^{6}\mathrm{Li}\ensuremath{-}^{7}\mathrm{Li}$ mixtures, which were proven to be a successful system for the study of impurity physics and Bose-Fermi superfluids.