Spin-conservation propensity rule for three-body recombination of ultracold Rb atoms

TL;DR

This study investigates the validity of a hyperfine spin conservation rule in three-body recombination of ultracold rubidium isotopes, confirming its applicability to $^{85}$Rb and analyzing the underlying physical principles.

Contribution

The paper extends the understanding of the spin-conservation propensity rule from $^{87}$Rb to $^{85}$Rb, providing experimental evidence and theoretical insights into its general validity.

Findings

The propensity rule holds for $^{85}$Rb across a range of binding energies.

Experimental mapping of molecular spin states supports the rule's applicability.

Theoretical analysis explains the physical origin of the spin conservation in recombination.

Abstract

We explore the physical origin and the general validity of a propensity rule for the conservation of the hyperfine spin state in three-body recombination. This rule was recently discovered for the special case of $^{87}$Rb with its nearly equal singlet and triplet scattering lengths. Here, we test the propensity rule for $^{85}$Rb for which the scattering properties are very different from $^{87}$Rb. The Rb$_2$ molecular product distribution is mapped out in a state-to-state fashion using REMPI detection schemes which fully cover all possible molecular spin states. Interestingly, for the experimentally investigated range of binding energies from zero to $\sim13\:\textrm{GHz}\times h$ we observe that the spin-conservation propensity rule also holds for $^{85}$Rb. From these observations and a theoretical analysis we derive an understanding for the conservation of the hyperfine spin state. We identify several criteria to judge whether the propensity rule will also hold for other elements and collision channels.