Feshbach resonances with large background scattering length: interplay with open-channel resonances

TL;DR

This paper develops an analytical model that incorporates both Feshbach and open-channel resonances, especially relevant for systems with large background scattering lengths, improving understanding and accuracy over single-resonance models.

Contribution

The authors introduce a simple analytical model accounting for open-channel resonances alongside Feshbach resonances, extending the applicability of resonance descriptions in atomic systems.

Findings

Model shows excellent agreement with coupled-channels calculations for $^{85}$Rb.

Applicable to other systems like $^6$Li and $^{133}$Cs with large background scattering.

Provides deeper insight into the physics of open-channel and Feshbach resonance interplay.

Abstract

Feshbach resonances are commonly described by a single-resonance Feshbach model, and open-channel resonances are not taken into account explicitly. However, an open-channel resonance near threshold limits the range of validity of this model. Such a situation exists when the background scattering length is much larger than the range of the interatomic potential. The open-channel resonance introduces strong threshold effects not included in the single-resonance description. We derive an easy-to-use analytical model that takes into account both the Feshbach resonance and the open-channel resonance. We apply our model to $^{85}$Rb, which has a large background scattering length, and show that the agreement with coupled-channels calculations is excellent. The model can be readily applied to other atomic systems with a large background scattering length, such as $^6$Li and $^{133}$Cs. Our approach provides full insight into the underlying physics of the interplay between open-channel (or potential) resonances and Feshbach resonances.