Two-colour laser cooling for 40K-87Rb quantum gas mixtures

Abstract

We present an efficient cooling scheme for fermionic ${}^{40}\text{K}$ atoms, using laser light red and blue detuned with respect to the $\mathcal{D}2$ and $\mathcal{D}1$ principle flourescence lines, respectively. The cooling scheme is found to significantly increase the saturation level for loading of a ${}^{40}\text{K}$ magneto-optical trap (MOT), resulting in increased atom numbers or decreased cycle times. While the attainable ${}^{40}\text{K}$ atom number is approximately doubled if exclusively ${}^{40}\text{K}$ atoms are cooled, the scheme is particularly powerful for dual-species MOTs, for example, if ${}^{40}\text{K}$ and ${}^{87}\text{Rb}$ atoms are cooled simultaneously in the same MOT configuration. The typical atom losses due to light-assisted hetero-nuclear collisions between ${}^{40}\text{K}$ and ${}^{87}\text{Rb}$ seem to be reduced giving rise to a threefold improvement of the ${}^{40}\text{K}$ atom number as compared to that in a conventional dual-species MOT, operating merely with $\mathcal{D}2$ light. Our scheme can be a useful extension to most dual-species experiments, aiming to reach simultaneous degeneracy of both species.

8 pages, 5 figures