Preparation of 87Rb and 133Cs in the motional ground state of a single optical tweezer

Abstract

We report simultaneous Raman sideband cooling of a single 87Rb atom and a single 133Cs atom held in separate optical tweezers at 814 nm and 938 nm, respectively. Starting from outside the Lamb-Dicke regime, after 45 ms of cooling we measure probabilities to occupy the three-dimensional motional ground state of $0.8{6}_{-0.04}^{+0.03}$ for Rb and $0.9{5}_{-0.04}^{+0.03}$ for Cs. Our setup overlaps the Raman laser beams used to cool Rb and Cs, reducing hardware requirements by sharing equipment along the same beam path. The cooling protocol is scalable, and we demonstrate cooling of single Rb atoms in an array of four tweezers. After motional ground-state cooling, a 938 nm tweezer is translated to overlap with a 814 nm tweezer so that a single Rb and a single Cs atom can be transferred into a common 1064 nm trap. By minimising the heating during the merging and transfer, we prepare the atoms in the relative motional ground state with an efficiency of $0.8{1}_{-0.08}^{+0.08}$. This is a crucial step towards the formation of single RbCs molecules confined in optical tweezer arrays.