Thermalization measurements on an ultracold mixture of metastable $^4$He and $^{87}$Rb atoms in a quadrupole magnetic trap

TL;DR

This paper reports on thermalization measurements of an ultracold metastable helium-4 and rubidium-87 mixture in a magnetic trap, providing insights into interspecies interactions and scattering lengths.

Contribution

It introduces a theoretical model for interspecies thermalization in a quadrupole trap considering Majorana heating and a method to extract scattering lengths from elastic cross sections.

Findings

Measured an upper limit of the interspecies two-body loss rate coefficient.

Provided a theoretical framework for thermalization including Majorana heating effects.

Determined the metastable helium-rubidium scattering length from experimental data.

Abstract

Recently we have reported (Knoop et al. [arXiv:1404.4826]) on an experimental determination of metastable triplet $^4$He+$^{87}$Rb scattering length by performing thermalization measurements for an ultracold mixture in a quadrupole magnetic trap. Here we present our experimental apparatus and elaborate on these thermalization measurements. In particular we give a theoretical description of interspecies thermalization rate for a quadrupole magnetic trap, i. e. in the presence of Majorana heating, and a general procedure to extract the scattering length from the elastic cross section at finite temperature based on knowledge of the $C_6$ coefficient alone. In addition, from our thermalization data we obtain an upper limit of the total interspecies two-body loss rate coefficient of $1.5\times 10^{-12}$ cm$^3$s$^{-1}$.