Probing open- and closed-channel p-wave Feshbach resonances

We study a p-wave Feshbach resonance in potassium-40 with a combination of spectroscopic binding energy measurements, coupled-channels calculations, and a two-channel model [1]. Using both resonant association and spin-flip association, the binding energy of bound and quasi-bound dimers is measured across a five-gauss range. Our scattering model incorporates the ramping closed-channel state, weak dipole-dipole interactions, and a low-lying p-wave shape resonance in the open channel. The open-channel resonance affects low energy scattering and creates nonlinearity in the binding energy near threshold, which resolves an open question [2]. We explain why in the low-energy limit a divergent contribution to the scattering volume from dipole-dipole interactions violates the p-wave threshold law, and how we isolate the contribution of the short-range potentials to scattering. Our improved understanding of p-wave scattering near this resonance enables quantitative testing of predictions for low-dimensional odd-wave gases, and lays a basis for future few- and many-body p-wave experiments.

[1] D. J. M. Ahmed-Braun, K. G. Jackson, S. Smale, C. J. Dale, B. A. Olsen, S. J. J. M. F. Kokkelmans, P. S. Julienne, J. H. Thywissen, Probing open- and closed-channel p-wave resonances, arXiv:2101.02700 (2021).

[2] J. P. Gaebler, J. T. Stewart, J. L. Bohn, and D. S. Jin, p-wave Feshbach molecules, Phys. Rev. Lett. 98, 200403 (2007).