Realization of a Resonant Fermi Gas with a Large Effective Range

TL;DR

This paper reports the experimental measurement of a resonant Fermi gas with a large effective range, revealing energy-dependent interactions and enhanced three-body recombination near a narrow Feshbach resonance, which challenges contact potential models.

Contribution

It demonstrates the realization and characterization of a Fermi gas with an anomalously large effective range near a narrow Feshbach resonance, providing new insights into strongly correlated quantum gases.

Findings

Interaction energy is strongly energy dependent.

Behavior cannot be described by contact potential alone.

Three-body recombination is enhanced near the resonance.

Abstract

We have measured the interaction energy and three-body recombination rate for a two-component Fermi gas near a narrow Feshbach resonance and found both to be strongly energy dependent. Even for deBroglie wavelengths greatly exceeding the van der Waals length scale, the behavior of the interaction energy as a function of temperature cannot be described by atoms interacting via a contact potential. Rather, energy-dependent corrections beyond the scattering length approximation are required, indicating a resonance with an anomalously large effective range. For fields where the molecular state is above threshold, the rate of three-body recombination is enhanced by a sharp, two-body resonance arising from the closed-channel molecular state which can be magnetically tuned through the continuum. This narrow resonance can be used to study strongly correlated Fermi gases that simultaneously have a sizeable effective range and a large scattering length.