Theory of Combined Photoassociation and Feshbach Resonances in a Bose-Einstein Condensate

TL;DR

This paper develops a theoretical model for combined photoassociation and Feshbach resonances in a Bose-Einstein condensate, revealing quantum interference effects, resonance shifts, and rate limits influenced by experimental parameters.

Contribution

It introduces an analytical model that captures the interplay of photoassociation and Feshbach resonances, including quantum interference and dispersive shifts, validated by numerical experiments.

Findings

Constructive interference enables saturation of photoassociation rate at accessible intensities.

Rate limits depend on condensate density and approach the magnetoassociation limit near Feshbach resonance.

Dispersive-like shifts are tunable and depend on molecule size, indicating non-universal physics.

Abstract

We model combined photoassociation and Feshbach resonances in a Bose-Einstein condensate, where the shared dissociation continuum allows for quantum interference in losses from the condensate, as well as a dispersive-like shift of resonance. A simple analytical model, based on the limit of weakly bound molecules, agrees well with numerical experiments that explicitly include dissociation to noncondensate modes. For a resonant laser and an off-resonant magnetic field, constructive interference enables saturation of the photoassociation rate at user-friendly intensities, at a value set by the interparticle distance. This rate limit is larger for smaller condensate densities and, near the Feshbach resonance, approaches the rate limit for magnetoassociation alone. Also, we find agreement with the unitary limit--set by the condensate size--only for a limited range of near-resonant magnetic fields. Finally, for a resonant magnetic field and an off-resonant laser, magnetoassociation displays similar quantum interference and a dispersive-like shift. Unlike photoassociation, interference and the fieldshift in resonant magnetoassociation is tunable with both laser intensity and detuning. Also, the dispersive-like shift of the Feshbach resonance depends on the size of the Feshbach molecule, and is a signature of non-universal physics in a strongly interacting system.