Cross-dimensional relaxation of $^7$Li-$^{87}$Rb atomic gas mixtures in a spherical-quadrupole magnetic trap

TL;DR

This study measures the interaction strength between $^7$Li and $^{87}$Rb atoms in a spherical quadrupole magnetic trap by analyzing cross-dimensional relaxation, revealing faster relaxation than theoretical predictions suggest.

Contribution

It provides the first experimental measurement of interspecies interaction strength in this atomic mixture using cross-dimensional relaxation in a spherical quadrupole trap.

Findings

Observed relaxation occurs faster than theoretical predictions.

Experimental results challenge existing molecular potential models.

Calibrated measurements using $^{87}$Rb-only gas relaxation.

Abstract

We measure the interspecies interaction strength between $^7$Li and $^{87}$Rb atoms through cross-dimensional relaxation of two-element gas mixtures trapped in a spherical quadrupole magnetic trap. We record the relaxation of an initial momentum-space anisotropy in a lithium gas when co-trapped with rubidium atoms, with both species in the $|F=1, m_F = -1\rangle$ hyperfine state. Our measurements are calibrated by observing cross-dimensional relaxation of a $^{87}$Rb-only trapped gas. Through Monte Carlo simulations, we compare the observed relaxation to that expected given the theoretically predicted energy-dependent differential cross section for $^7$Li-$^{87}$Rb collisions. The experimentally observed relaxation occurs significantly faster than predicted theoretically, a deviation that appears incompatible with other experimental data characterising the $^7$Li-$^{87}$Rb molecular potential.