Understanding chemical reactions in a quantum degenerate gas of polar molecules via complex formation

TL;DR

This paper develops a model to explain the suppressed chemical reaction rates in a quantum degenerate gas of polar molecules, highlighting the role of complex formation and many-body effects beyond simple two-body collisions.

Contribution

It introduces a novel effective model incorporating complex-molecule interactions and many-body effects to explain reaction suppression in ultracold polar molecules.

Findings

Pure two-body losses cannot explain the suppression.

Effective many-body interactions reproduce experimental observations.

Higher-order processes are likely responsible for reaction suppression.

Abstract

A recent experiment reported for the first time the preparation of a Fermi degenerate gas of polar molecules and observed a suppression of their chemical reaction rate compared to the one expected from a purely classical treatment. While it was hypothesized that the suppression in the ultracold regime had its roots in the Fermi statistics of the molecules, this argument is inconsistent with the fact that the Fermi pressure should set a lower bound for the chemical reaction rate. Therefore it can not be explained from standard two-body $p$-wave inelastic collisions. Here we develop a simple model of chemical reactions that occur via the formation and decay of molecular complexes. We indeed find that pure two-body molecule losses are unable to explain the observed suppression. Instead we extend our description beyond two-body physics by including effective complex-molecule interactions possible emerging from many-body and effective medium effects at finite densities and in the presence of trapping light. %Under this framework we observe that additional complex-molecule collisions, which manifest as a net three-body molecular interaction could give rise to the additional suppression. Although our effective model is able to quantitatively reproduce recent experimental observations, a detailed understanding of the actual physical mechanism responsible for these higher-order interaction processes is still pending.