Evolution of the unitary Bose gas for broad to narrow Feshbach resonances

TL;DR

This paper investigates the dynamics of unitary Bose gases across different Feshbach resonance widths, revealing how density influences molecule formation, quantum depletion, and early-time growth behaviors, with insights into two-body bound states.

Contribution

It introduces a two-channel model to analyze how density variations affect the evolution of unitary Bose gases, highlighting the transition from open to closed-channel dominated dimers due to many-body effects.

Findings

Increased density enhances closed-channel molecule production.

Quantum depletion buildup decreases with higher density.

Early-time two-body contact growth shifts from linear to quadratic.

Abstract

We study the post-quench dynamics of unitary Bose gases using a two-channel model, focusing on the effect of variations in the width of the Feshbach resonance due to density changes. We generally find that increasing the density leads to a corresponding increase in the production of closed channel molecules, a decrease in the build up of quantum depletion and a transition from linear to quadratic early-time growth of the two-body contact as well as the condensed pair fraction. Motivated by the presence of closed-channel molecules in the unitary regime, we study the embedded two-body problem finding a transition from open to closed-channel dominated dimers due to many-body effects.