Universality of the three-body Efimov parameter at narrow Feshbach resonances

TL;DR

This study investigates the universality of the three-body Efimov parameter at narrow Feshbach resonances in ultracold 39K atoms, revealing unexpected universal behavior across different resonance types.

Contribution

It demonstrates that the three-body parameter remains approximately universal at narrow Feshbach resonances, contrary to theoretical expectations for non-universal coupling regimes.

Findings

Universal relation of three-body parameter with van der Waals radius observed

Three-body spectrum determined by single-channel model despite narrow resonances

Evidence for a new regime in three-body scattering at narrow Feshbach resonances

Abstract

We measure the critical scattering length for the appearance of the first three-body bound state, or Efimov three-body parameter, at seven different Feshbach resonances in ultracold 39K atoms. We study both intermediate and narrow resonances, where the three-body spectrum is expected to be determined by the non-universal coupling of two scattering channels. We observe instead approximately the same universal relation of the three-body parameter with the two-body van der Waals radius already found for broader resonances, which can be modeled with a single channel. This unexpected observation suggests the presence of a new regime for three-body scattering at narrow resonances.