Direct observation of Feshbach enhanced $s$-wave scattering of fermions

Abstract

We directly measured the normalized $s$-wave scattering cross-section of ultracold ${}^{40}\mathrm{K}$ 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.

22 pages, 11 figues

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• Quantum degenerate dipolar Fermi gas
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