Molecule-molecule and atom-molecule collisions with ultracold RbCs molecules

TL;DR

This study investigates ultracold RbCs molecule collisions, demonstrating partial suppression of collisional loss via optical trap modulation and analyzing atom-molecule collision rates, providing insights into loss mechanisms and control methods.

Contribution

It presents the first detailed analysis of molecule-molecule and atom-molecule collisions involving ultracold RbCs, including suppression techniques and rate measurements.

Findings

Partial suppression of collisional loss with trap modulation.

Loss rates scale linearly with atom density.

Measured loss rates are below the universal limit.

Abstract

Understanding ultracold collisions involving molecules is of fundamental importance for current experiments, where inelastic collisions typically limit the lifetime of molecular ensembles in optical traps. Here we present a broad study of optically trapped ultracold RbCs molecules in collisions with one another, in reactive collisions with Rb atoms, and in nonreactive collisions with Cs atoms. For experiments with RbCs alone, we show that by modulating the intensity of the optical trap, such that the molecules spend 75% of each modulation cycle in the dark, we partially suppress collisional loss of the molecules. This is evidence for optical excitation of molecule pairs mediated via sticky collisions. We find that the suppression is less effective for molecules not prepared in the spin-stretched hyperfine ground state. This may be due either to longer lifetimes for complexes or to laser-free decay pathways. For atom-molecule mixtures, RbCs+Rb and RbCs+Cs, we demonstrate that the rate of collisional loss of molecules scales linearly with the density of atoms. This indicates that, in both cases, the loss of molecules is rate-limited by two-body atom-molecule processes. For both mixtures, we measure loss rates that are below the thermally averaged universal limit.