A high phase-space density mixture of $^{87}$Rb and $^{133}$Cs: towards ultracold heteronuclear molecules

TL;DR

This paper demonstrates the production of a high phase-space density mixture of rubidium-87 and cesium-133 atoms, observes an interspecies Feshbach resonance, and creates Cs₂ molecules, advancing towards ultracold heteronuclear molecule formation.

Contribution

It introduces a simple experimental setup for sympathetic cooling of Rb and Cs, measures interspecies collision rates, and reports the first observation of an interspecies Feshbach resonance in this mixture.

Findings

Achieved near quantum degeneracy phase-space densities for both species.

Observed an interspecies Feshbach resonance at 181.7 G.

Created Cs₂ molecules via magneto-association at 19.8 G.

Abstract

We report the production of a high phase-space density mixture of $^{87}$Rb and $^{133}$Cs atoms in a levitated crossed optical dipole trap as the first step towards the creation of ultracold RbCs molecules via magneto-association. We present a simple and robust experimental setup designed for the sympathetic cooling of $^{133}$Cs via interspecies elastic collisions with $^{87}$Rb. Working with the $|F=1, m_F=+1 >$ and the $|3, +3 >$ states of $^{87}$Rb and $^{133}$Cs respectively, we measure a high interspecies three-body inelastic collision rate $\sim 10^{-25}-10^{-26} \rm{cm}^{6}\rm{s}^{-1}$ which hinders the sympathetic cooling. Nevertheless by careful tailoring of the evaporation we can produce phase-space densities near quantum degeneracy for both species simultaneously. In addition we report the observation of an interspecies Feshbach resonance at 181.7(5) G and demonstrate the creation of Cs$_{2}$ molecules via magneto-association on the 4g(4) resonance at 19.8 G. These results represent important steps towards the creation of ultracold RbCs molecules in our apparatus.