Close-coupled model of Feshbach resonances in ultracold and atomic collisions

Helium atoms in the metastable state () have unique advantages for ultracold atomic experiments. However, there is no known accessible Feshbach resonance in which could be used to manipulate the scattering length and hence unlock several new experimental possibilities. Previous experimental and theoretical studies for have produced contradictory results. We aimed to resolve this discrepancy with a theoretical search for Feshbach resonances, using a close-coupled model of collisions in the presence of an external magnetic field. Several resonances were detected and the existing literature discrepancy was resolved. Although none of the resonances identified are readily experimentally usable, an interesting non-Feshbach scattering length variation with magnetic field was observed in heteronuclear collisions, at field strengths that are experimentally accessible.