%0 Journal Article %J Nature Communications %D 2017 %T Above threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider %A Milena S. J. Horvath %A Ryan Thomas %A Eite Tiesinga %A Amita B. Deb %A Niels Kjærgaard %X

Studies of magnetically tunable Feshbach resonances in ultracold atomic gases have predominantly been carried out in the zero collision-energy limit. Here, we explore above threshold collisions at well-defined energies in the vicinity of a narrow magnetic Feshbach resonance by means of a laser-based collider. Our experiment focuses on collisions between ground-state 87Rb atoms in the |F = 2,mF = 0i and |F = 1,mF = 1i hyperfine states, which have a known s-wave resonance at 9.040(7) G at threshold that strongly couples to inelastic channels, where 1 G = 10−4 T. Using our collider we can track the magnetic field shift in resonance position as the energy is tuned. This presents a challenge due to the narrow width of the resonance in conjunction with inherent broadening mechanisms of the collider. We find, however, that the narrow Feshbach scattering feature becomes imprinted on the spatial distribution of atoms in a fashion that allows for an accurate determination of resonance position as a function of collision energy through a shift in center-of-mass position of the outgoing clouds. This shift has a dispersive line shape with a zero value at the resonance position. We obtain excellent agreement with theory on the resonance position.

%B Nature Communications %V 8 %8 2017/09/06 %G eng %U https://arxiv.org/abs/1704.07109 %N 452 %R 10.1038/s41467-017-00458-y %0 Journal Article %J Physical Review A %D 2017 %T Dispersive optical detection of magnetic Feshbach resonances in ultracold gases %A Bianca J. Sawyer %A Milena S. J. Horvath %A Eite Tiesinga %A Amita B. Deb %A Niels Kjærgaard %X

Magnetically tunable Feshbach resonances in ultracold atomic systems are chiefly identified and characterized through time consuming atom loss spectroscopy. We describe an off-resonant dispersive optical probing technique to rapidly locate Feshbach resonances and demonstrate the method by locating four resonances of 87Rb, between the |F=1,mF=1 and |F=2,mF=0 states. Despite the loss features being 100 mG wide, we require only 21 experimental runs to explore a magnetic field range >18 G. The resonances consist of two known s-wave features in the vicinity of 9 G and 18 G and two previously unobserved p-wave features near 5 G and 10 G. We further utilize the dispersive approach to directly characterize the two-body loss dynamics for each Feshbach resonance.

%B Physical Review A %V 96 %P 022705 %8 2017/08/18 %G eng %U https://arxiv.org/abs/1702.02216 %N 2 %R 10.1103/PhysRevA.96.022705