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

TL;DR

This paper demonstrates simultaneous Raman sideband cooling of single rubidium and cesium atoms in optical tweezers, achieving high ground state occupation probabilities and enabling their transfer into a common trap for molecule formation.

Contribution

It introduces a scalable cooling protocol for Rb and Cs atoms in separate tweezers and demonstrates their transfer into a shared trap, advancing quantum control techniques.

Findings

Achieved 86% Rb and 95% Cs ground state occupation probabilities.

Successfully cooled Rb atoms in an array of four tweezers.

Prepared atom pairs in a shared trap with 81% efficiency.

Abstract

We report simultaneous Raman sideband cooling of a single $^{87}$Rb atom and a single $^{133}$Cs 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 0.86$^{+0.03}_{-0.04}$ for Rb and 0.95$^{+0.03}_{-0.04}$ 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 0.81$^{+0.08}_{-0.08}$. This is a crucial step towards the formation of single RbCs molecules confined in optical tweezer arrays.