The prospects of sympathetic cooling of NH molecules with Li atoms

TL;DR

This study investigates the potential for sympathetic cooling of NH molecules with Li atoms by calculating collision cross sections and analyzing the effects of potential energy surface variations, finding favorable conditions below 20 mK.

Contribution

The paper provides detailed calculations of collision dynamics between Li and NH, demonstrating the feasibility of sympathetic cooling in ultracold regimes and analyzing resonance effects.

Findings

Spin-stretched states suppress spin-relaxation collisions.

Feshbach resonances cause fluctuations in cross sections at ultracold temperatures.

Most potential energy surfaces yield favorable elastic-to-inelastic ratios below 20 mK.

Abstract

We calculate the quartet potential energy surface for Li+NH and use it to calculate elastic and spin-relaxation cross sections for collisions in magnetically trappable spin-stretched states. The potential is strongly anisotropic but spin-relaxation collisions are still suppressed by centrifugal barriers when both species are in spin-stretched states. In the ultracold regime, both the elastic and inelastic cross sections fluctuate dramatically as the potential is varied because of Feshbach resonances. The potential-dependence is considerably reduced at higher energies. The major effect of using an unconverged basis set in the scattering calculations is to shift the resonances without changing their general behaviour. We have calculated the ratio of elastic and spin-relaxation cross sections, as a function of collision energy and magnetic field, for a variety of potential energy surfaces. Most of the surfaces produce ratios that are favorable for sympathetic cooling, at temperatures below about 20 mK.