Fitting ultracold resonances without a fit

TL;DR

This paper introduces a numerical method to extract Feshbach resonance parameters directly from calculations, avoiding traditional fitting procedures, and provides a rigorous lineshape for overlapping inelastic resonances.

Contribution

It presents a novel numerical approach based on reactance matrix decomposition that works for inelastic overlapping resonances, improving analysis accuracy.

Findings

Method accurately extracts resonance parameters without fitting.

Derived a rigorous lineshape for overlapping inelastic resonances.

Applicable to general inelastic resonance scenarios.

Abstract

We present a numerical procedure allowing one to extract Feshbach resonance parameters from numerical calculations without relying on approximate fitting procedures. Our approach is based on a simple decomposition of the reactance matrix in terms of poles and residual background contribution, and can be applied to the general situation of inelastic overlapping resonances. A simple lineshape for overlapping inelastic resonances, equivalent to known results in the particular cases of isolated and overlapping elastic features, is also rigorously derived.