Observation of Efimov Universality across a Non-Universal Feshbach Resonance in \textsuperscript{39}K

TL;DR

This study investigates Efimov physics in ultracold extsuperscript{39}K near a non-universal Feshbach resonance, revealing universal scaling behavior in most features but deviations near the effective range scale.

Contribution

It provides the first detailed measurement of Efimov features in extsuperscript{39}K near a non-universal resonance, highlighting the impact of finite effective range on universality.

Findings

Four Efimov features identified at large scattering lengths.

Three features follow universal scaling within 10%.

One feature deviates due to proximity to effective range.

Abstract

We study three-atom inelastic scattering in ultracold \textsuperscript{39}K near a Feshbach resonance of intermediate coupling strength. The non-universal character of such resonance leads to an abnormally large Efimov absolute length scale and a relatively small effective range $r_e$, allowing the features of the \textsuperscript{39}K Efimov spectrum to be better isolated from the short-range physics. Meticulous characterization of and correction for finite temperature effects ensure high accuracy on the measurements of these features at large-magnitude scattering lengths. For a single Feshbach resonance, we unambiguously locate four distinct features in the Efimov structure. Three of these features form ratios that obey the Efimov universal scaling to within 10\%, while the fourth feature, occurring at a value of scattering length closest to $r_e$, instead deviates from the universal value.