Comparison of an efficient implementation of gray molasses to narrow-line cooling for the all-optical production of a lithium quantum gas

Abstract

We present an efficient scheme to implement a gray optical molasses for sub-Doppler cooling of Li6 atoms with minimum experimental overhead. To integrate the D1 light for the gray molasses cooling into the same optical setup that is used for the D2 light for a standard magneto-optical trap (MOT), we rapidly switch the injection seeding of a slave laser between the D2 and the D1 light sources. Switching times as short as 30 μs can be achieved, inferred from monitor optical beat signals. The resulting low-intensity molasses cools a sample of N=9×108 atoms to about 60 μK. A maximum phase-space density of ρ=1.2×10-5 is observed. On the same setup, the performance of the GM is compared to that of narrow-line cooling in an ultraviolet (UV) MOT, following the procedure in Sebastian et al. [J. Sebastian, Ch. Gross, K. Li, H. C. J. Gan, W. Li, and K. Dieckmann, Phys. Rev. A 90, 033417 (2014)PLRAAN1050-294710.1103/PhysRevA.90.033417]. Further, we compare the production of a degenerate Fermi gas using both methods. Loading an optical dipole trap from the gray molasses yields a quantum degenerate sample with 3.3×105 atoms, while loading from the denser UV MOT yields 2.4×106 atoms. Where the highest atom numbers are not a priority this implementation of the gray molasses technique yields sufficiently large samples for a comparatively low technical effort.