%0 Journal Article %J Nature Communications %D 2018 %T Observation of bound state self-interaction in a nano-eV atom collider %A Ryan Thomas %A Matthew Chilcott %A Eite Tiesinga %A Amita B. Deb %A Niels Kjærgaard %X
Quantum mechanical scattering resonances for colliding particles occur when a continuum scattering state couples to a discrete bound state between them. The coupling also causes the bound state to interact with itself via the continuum and leads to a shift in the bound state energy, but, lacking knowledge of the bare bound state energy, measuring this self-energy via the resonance position has remained elusive. Here, we report on the direct observation of self-interaction by using a nano-eV atom collider to track the position of a magnetically-tunable Feshbach resonance through a parameter space spanned by energy and magnetic field. Our system of potassium and rubidium atoms displays a strongly non-monotonic resonance trajectory with an exceptionally large self-interaction energy arising from an interplay between the Feshbach bound state and a different, virtual bound state at a fixed energy near threshold.
%B Nature Communications %V 9 %8 2018/11/20 %G eng %U https://arxiv.org/abs/1807.01174 %N 4895 %R https://doi.org/10.1038/s41467-018-07375-8 %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 %XStudies 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 %XMagnetically 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
The wavefunction for indistinguishable fermions is anti-symmetric under particle exchange, which directly leads to the Pauli exclusion principle, and hence underlies the structure of atoms and the properties of almost all materials. In the dynamics of collisions between two indistinguishable fermions this requirement strictly prohibits scattering into 90 degree angles. Here we experimentally investigate the collisions of ultracold clouds fermionic