Simultaneous Sub-Doppler laser cooling of ⁶Li and ⁷Li isotopes

Ultracold atoms provide an ideal platform for probing mixtures of quantum gases. A successful example of such systems is the Bose-Fermi superfluid mixture of Lithium 6 and Lithium 7 isotopes [1, 2, 3]. However, the preparation of such systems comes with a significant technical overhead. Here, we propose a simplification of the preparation protocol by demonstrating the simultaneous sub-Doppler cooling of Lithium 6 and Lithium 7. The method is based on gray molasses and operates with positive detuning on the D1 atomic transition for the respective isotopes. We circumvent the proximity of the D1 transition of Lithium 7 to the D2 transition of Lithium 6, by applying an alternating laser beam pulse sequence on both isotopes. We obtain temperatures of 190 µK and 70 µK and atom numbers of 5×10⁷ and 1×10⁸ for Lithium 6 and Lithium 7, respectively. This Bose-Fermi mixture is a good starting point for  loading into an optical dipole trap and evaporative cooling to quantum degeneracy.

 

[1]          I. Ferrier-Barbut et al., Science 345, 1035 (2014)

[2]          M. Delahaye et al., PRL 115, 265303 (2015)

[3]          S. Laurent et al., PRL 118, 103403 (2017)