Cold atomic and molecular collisions: approaching the universal loss regime

TL;DR

This paper explores a simplified single-channel model for cold atomic and molecular collisions, demonstrating its increasing accuracy with higher rotational states and potential to predict loss rates without complex calculations.

Contribution

It introduces a single-parameter model for inelastic and reactive processes in cold collisions and validates it against coupled-channel calculations across different rotational states.

Findings

Single-channel model's accuracy improves with higher rotational quantum numbers.

Model can predict loss rate ranges at higher energies without detailed coupled-channel calculations.

Results suggest potential for simplified estimation of collision loss rates in ultracold regimes.

Abstract

We investigate the behaviour of single-channel theoretical models of cold and ultracold collisions that take account of inelastic and reactive processes using a single parameter to represent short-range loss. We present plots of the resulting energy-dependence of elastic and inelastic or reactive cross sections over the full parameter space of loss parameters and short-range phase shifts. We then test the single-channel model by comparing it with the results of coupled-channel calculations of rotationally inelastic collisions between LiH molecules and Li atoms. We find that the range of cross sections predicted by the single-channel model becomes increasingly accurate as the initial LiH rotational quantum number increases, with a corresponding increase in the number of open loss channels. The results suggest that coupled-channel calculations at very low energy (in the s-wave regime) could in some cases be used to estimate a loss parameter and then to predict the range of possible loss rates at higher energy, without the need for explicit coupled-channel calculations for higher partial waves.