Feshbach enhanceds-wave scattering of fermions: direct observation with optimized absorption imaging

Abstract

We directly measured the normalized s-wave scattering cross-section of ultracold 40K 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 B0 = 20.206(15) mT with width Δ = 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.

Multiple scattering dynamics of fermions at an isolated p-wave resonance

“…In conclusion, we have analysed the effect of multiple scattering on the particle distributions resulting from spin-polarized 40 K collisions in an energy domain where every binary scattering event is exclusively p-wave. Contrary to the notion that fermionic clouds of 40 K would not have sufficient densities or inter-atomic interactions to readily observe scattering halos 27 , we not only directly and clearly image such halos but also observe 90° scattering as a clear indication of multiple scattering. Our data, along with a numerical simulation of the experiment, enable us to classify the collisions into three regions based on the prevalence and effect of multiple scattering on the angular and radial distributions ( Supplementary Note 3 discusses the radial aspect).…”

Above-threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider

“…We have investigated the collision of two individually prepared clouds of ultracold atoms about a narrow Feshbach resonance with a significant inelastic component. Previous experiments with colliding clouds successfully analysed the halos 9.05 9.06 9.07 9.08 9.09 9.1 9.11 9.12 9.13 0 of particles that elastically scattered from incident samples to infer properties about their interaction 23,24,28,[40][41][42][43][44] . While a collisional halo also ensues from the process considered in this study 45 , its resonant enhancement is difficult to attain due to thermal broadening and the existence of three dominant exit channels.…”

“…Recently, both experimental and theoretical collider-type approaches that consider energy as a tuning parameter for Feshbach resonances have emerged [25][26][27][28] . For example, Gensemer et al 27 explored resonant scattering behavior with respect to the relative collision energy through use of an atomic fountain that launched ultracold clouds of 133 Cs atoms to collide in free space at a fixed magnetic bias field.…”

Appropriate Probe Condition for Absorption Imaging of Ultracold6Li Atoms

“…We note that there is another photon recoil effect to distort absorption images. That is defocussing effect caused by moving atoms with respect to the object plane due to photon recoils [9,6]. The degree of this effect depends on t and s. In our imaging condition as shown in Fig.…”