Finite range corrections near a Feshbach resonance and their role in the Efimov effect

TL;DR

This paper measures the binding energy of lithium Feshbach molecules deep into the non-universal regime, refines the scattering length determination, and investigates how finite range effects influence the Efimov effect near a Feshbach resonance.

Contribution

It introduces methods to correct for non-universal short-range effects in scattering length measurements and reanalyzes Efimov features considering finite range corrections.

Findings

Field-dependent effective range corrections match experimental data.

Refined scattering length vs. magnetic field relationship.

Finite range effects significantly influence Efimov resonance positions.

Abstract

We have measured the binding energy of $^7$Li Feshbach molecules deep into the non-universal regime by associating free atoms in a Bose-Einstein condensate by modulating the magnetic field. We extract the scattering length from these measurements, correcting for non-universal short-range effects using several different methods. We find that field-dependent effective range corrections agree well with the data. With this more precise determination of the scattering length vs. field we reanalyze our previous data on the location of atom loss features produced by the Efimov effect \cite{PollackSci09} and investigate effective range corrections to universal theory.