# Interspecies thermalization in an ultracold mixture of Cs and Yb in an optical trap

## TL;DR

This study measures and models interspecies thermalization between ultracold Cs and Yb, predicting scattering properties and demonstrating Bose-Einstein condensates, advancing quantum mixture research.

## Contribution

It provides the first experimental measurements and quantum scattering calculations of interspecies thermalization cross sections for Cs-Yb mixtures, and demonstrates simultaneous BEC production.

## Key findings

- Measured thermalization cross sections for Cs-Yb isotopic pairs.
- Optimized interaction potentials to match experimental data.
- Produced independent Bose-Einstein condensates of Cs and Yb.

## Abstract

We present measurements of interspecies thermalization between ultracold samples of $^{133}$Cs and either $^{174}$Yb or $^{170}$Yb. The two species are trapped in a far-off-resonance optical dipole trap and $^{133}$Cs is sympathetically cooled by Yb. We extract effective interspecies thermalization cross sections by fitting the thermalization measurements to a rate equation model, giving $\sigma_{\mathrm{Cs^{174}Yb}} = \left(5 \pm 2\right) \times 10^{-13} \, \mathrm{cm^{2}}$ and $\sigma_{\mathrm{Cs^{170}Yb}} = \left(18 \pm 8\right) \times 10^{-13} \, \mathrm{cm^{2}}$. We perform quantum scattering calculations of the thermalization cross sections and optimize the CsYb interaction potential to reproduce the measurements. We predict scattering lengths for all isotopic combinations of Cs and Yb. We also demonstrate the independent production of $^{174}$Yb and $^{133}$Cs Bose-Einstein condensates using the same optical dipole trap, an important step towards the realization of a quantum-degenerate mixture of the two species.