Probing open- and closed-channel p-wave resonances

TL;DR

This study investigates the complex physics of a strong p-wave Feshbach resonance in potassium-40, combining experiments and modeling to understand its molecular states, open- and closed-channel interactions, and the influence of shape resonances.

Contribution

It introduces a comprehensive two-channel model including dipole interactions and shape resonances, providing new insights into p-wave resonance behavior and classification as broad.

Findings

Observed nonlinear binding energy variation with magnetic field.

Identified a low-energy p-wave shape resonance in the open channel.

Classified the resonance as broad based on energy dependence analysis.

Abstract

We study the near-threshold molecular and collisional physics of a strong $^{40}$K p-wave Feshbach resonance through a combination of measurements, numerical calculations, and modeling. Dimer spectroscopy employs both radio-frequency spin-flip association in the MHz band and resonant association in the kHz band. Systematic uncertainty in the measured binding energy is reduced by a model that includes both the Franck-Condon overlap amplitude and inhomogeneous broadening. Coupled-channels calculations based on mass-scaled $^{39}$K potentials compare well to the observed binding energies and also reveal a low-energy p-wave shape resonance in the open channel. Contrary to conventional expectation, we observe a nonlinear variation of the binding energy with magnetic field, and explain how this arises from the interplay of the closed-channel ramping state with the near-threshold shape resonance in the open channel. We develop an analytic two-channel model that includes both resonances as well as the dipole-dipole interactions which, we show, become important at low energy. Using this parameterization of the energy dependence of the scattering phase, we can classify the studied $^{40}$K resonance as broad. Throughout the paper, we compare to the well understood s-wave case, and discuss the significant role played by van der Waals physics. The resulting understanding of the dimer physics of p-wave resonances provides a solid foundation for future exploration of few- and many-body orbital physics.