Alternative Route to Strong Interaction: Narrow Feshbach Resonance

TL;DR

This paper demonstrates that narrow Feshbach resonances induce significant strong interaction effects even when the bound state is not formed, due to a resonance phase shift structure affecting many scattering states.

Contribution

It reveals that narrow resonances cause asymmetric interaction energies on either side of the resonance, extending the understanding of strong interactions beyond the resonance width.

Findings

Strong interaction effects occur far from the bound state formation.

Asymmetry in interaction energy near the resonance is observed.

Experimental feasibility of measuring these effects is discussed.

Abstract

We show that a narrow resonance produces strong interaction effects far beyond its width on the side of the resonance where the bound state has not been formed. This is due to a resonance structure of its phase shift, which shifts the phase of a large number of scattering states by $\pi$ before the bound state emerges. As a result, the magnitude of the interaction energy when approaching the resonance on the "upper" and "lower" branch from different side of the resonance is highly asymmetric, unlike their counter part in wide resonances. Measurements of these effects are experimentally feasible.