Direct observation of Feshbach enhanced $\it{s}$-wave scattering of fermions

TL;DR

This study directly measured the s-wave scattering cross-section of ultracold fermions near a Feshbach resonance, providing precise resonance parameters and advanced imaging techniques for better atom number detection.

Contribution

The paper introduces a method to accurately measure scattering cross-sections and develops imaging techniques that improve signal-to-noise ratio in ultracold atom experiments.

Findings

Resonance location B0 = 20.206(15) mT

Resonance width Δ = 1.0(5) mT

Enhanced imaging techniques for atom number detection

Abstract

We directly measured the normalized $\it{s}$-wave scattering cross-section of ultracold $^{40}\rm{K}$ atoms across a magnetic-field Feshbach resonance by colliding pairs of degenerate Fermi gases (DFGs) and imaging the scattered atoms. We extracted the scattered fraction for a range of bias magnetic fields, and measured the resonance location to be $B_0 = 20.206(15)$ mT with width $\Delta = 1.0(5)$ mT. To optimize the signal-to-noise ratio of atom number in scattering images, we developed techniques to interpret absorption images in a regime where recoil induced detuning corrections are significant. These imaging techniques are generally applicable to experiments with lighter alkalis that would benefit from maximizing signal-to-noise ratio on atom number counting at the expense of spatial imaging resolution.