Very high precision bound state spectroscopy near a $^{85}$Rb Feshbach resonance

TL;DR

This study precisely measured the binding energy of a molecular state near a $^{85}$Rb Feshbach resonance in a BEC, using magnetic field pulses to induce and analyze atom-molecule oscillations, refining key resonance parameters.

Contribution

The paper provides highly accurate measurements of Feshbach resonance parameters and introduces a coupled-channels model fit to experimental data, improving understanding of $^{85}$Rb BEC interactions.

Findings

Resonance position at 155.041 G with 0.018 G uncertainty

Resonance width of 10.71 G with 0.02 G uncertainty

Evidence of a mean-field shift in binding energy

Abstract

We precisely measured the binding energy of a molecular state near the Feshbach resonance in a $^{85}$Rb Bose-Einstein condensate (BEC). Rapid magnetic field pulses induced coherent atom-molecule oscillations in the BEC. We measured the oscillation frequency as a function of B-field and fit the data to a coupled-channels model. Our analysis constrained the Feshbach resonance position [155.041(18) G], width [10.71(2) G], and background scattering length [-443(3) a$_0$] and yielded new values for $v_{DS}$, $v_{DT}$, and $C_6$. These results improved our estimate for the stability condition of an attractive BEC. We also found evidence for a mean-field shift to the binding energy.