We measure the interspecies interaction strength between 7Li and 87Rb 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 cotrapped with rubidium atoms, with both species in the |F=1,mF=−1⟩ hyperfine state. Our measurements are calibrated by observing cross-dimensional relaxation of a 87Rb-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 7Li−87Rb collisions. The experimentally observed relaxation occurs significantly faster than predicted theoretically, a deviation that appears incompatible with other experimental data characterizing the 7Li−87Rb molecular potential.
Cross-dimensional relaxation of 7 Li − 87 Rb atomic gas mixtures in a spherical-quadrupole magnetic trap