The multichannel nature of three-body recombination for ultracold $^{39}$K

TL;DR

This paper develops a multichannel spin model to study three-body recombination in ultracold potassium-39, accurately predicting Efimov resonance positions and analyzing the model's limitations at higher magnetic fields.

Contribution

It introduces a combined spin and interaction model that accurately predicts Efimov resonances and explores the approximation's validity across different magnetic fields.

Findings

Excellent agreement with experimental Efimov resonance data

Approximate model breaks down at higher magnetic fields

Multichannel couplings become significant near certain Feshbach resonances

Abstract

We develop a full multichannel spin model in momentum space to investigate three-body recombination of identical alkali-metal atoms colliding in a magnetic field. The model combines the exact three-atom spin structure and realistic pairwise atom-atom interactions. By neglecting the interaction between two particles when the spectating particle is not in its initial spin state we arrive at an approximate model. With this approximate model we achieve excellent agreement with the recent precise measurement of the ground Efimov resonance position in potassium-39 close to 33.58 G [Chapurin $et$ $al$., Phys. Rev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation by comparing to the numerical results for the full system and find that it breaks down for Feshbach resonances at larger magnetic fields in the same spin channel. There the relevant three-body closed channel thresholds are much closer to the open channel threshold, which enhances the corresponding multichannel couplings. Therefore the neglected components of the interaction should be included for those Feshbach resonances.