Testing universality of Efimov physics across broad and narrow Feshbach resonances

TL;DR

This study compares Efimov states in a Li-Cs mixture near broad and narrow Feshbach resonances, revealing that Efimov resonance positions depend on resonance strength and deviate from universal predictions in narrow resonances.

Contribution

It provides the first direct experimental comparison of Efimov spectra across broad and narrow Feshbach resonances, highlighting the non-universality in narrow resonances.

Findings

Efimov resonance positions vary with Feshbach resonance strength.

Universal predictions hold for broad but not narrow resonances.

Clear departure from universality observed in narrow Feshbach resonance.

Abstract

Efimov physics is a universal phenomenon arising in quantum three-body systems. For systems with resonant two-body interactions, Efimov predicted an infinite series of three-body bound states with geometric scaling symmetry. These Efimov states were first observed in cold Cs atoms and have since been reported in a variety of atomic systems. While theories predict non-universal behavior for narrow Feshbach resonances, experiments on Efimov resonances are so far consistent with predictions based on universal theories. Here we directly compare the Efimov spectra in a $^6$Li-$^{133}$Cs mixture near two Feshbach resonances which are very different in their resonance strengths but otherwise almost identical. Our result shows a clear dependence of the Efimov resonance positions on Feshbach resonance strength and a clear departure from the universal prediction for the narrow Feshbach resonance.