Probing Energy-Dependent Feshbach Resonances by Optical Control

TL;DR

This paper introduces an optical method to precisely control and probe narrow Feshbach resonances in ultracold gases, revealing detailed momentum-dependent scattering features and advancing the understanding of atomic interactions.

Contribution

It presents a two-field optical vernier technique that significantly enhances control over narrow Feshbach resonances in ultracold atoms, enabling detailed spectroscopic analysis.

Findings

Measured two-photon loss spectra in $^6$Li show complex structures.

Spectra agree well with theoretical models, validating the approach.

Observed anomalous frequency shifts remain unexplained.

Abstract

Optical control enables new high resolution probes of narrow collisional (Feshbach) resonances, which are strongly dependent on the relative momentum of colliding atom pairs, and important for simulating neutron matter with ultracold atomic gases. We demonstrate a two-field optical vernier, which expands kHz (mG) magnetic field detunings near a narrow resonance into MHz optical field detunings, enabling precise control and characterization of the momentum-dependent scattering amplitude. Two-photon loss spectra are measured for the narrow resonance in $^6$Li, revealing rich structure in very good agreement with our theoretical model. However, anomalous frequency shifts between the measured and predicted two-photon spectra are not yet explained.