<i>Ab initio</i> calculation of the spectrum of Feshbach resonances in NaLi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>+</mml:mo></mml:math> Na collisions
Tijs Karman, Marcin Gronowski, Michał Tomza, Juliana Park, Hyungmok Son, Yu‐Kun Lu, Alan O. Jamison, Wolfgang Ketterle
Abstract
We present a combined experimental and theoretical study of the spectrum of magnetically tunable Feshbach resonances in NaLi $({a}^{3}{\mathrm{\ensuremath{\Sigma}}}^{+})\phantom{\rule{4pt}{0ex}}+$ Na collisions. In the accompanying paper, J. J. Park, H. Son, Y.-K. Lu, T. Karman, M. Gronowski, M. Tomza, A. O. Jamison, and W. Ketterle, Phys. Rev. X 13, 031018 (2023), we observe experimentally 8 and 17 resonances occurring between $B=0$ and 1400 G in upper and lower spin-stretched states, respectively. Here, we perform ab initio calculations of the NaLi $+$ Na interaction potential and describe in detail the coupled-channel scattering calculations of the Feshbach resonance spectrum. The positions of the resonances cannot be predicted with realistic uncertainty in the state-of-the-art ab initio potential, but our calculations yield a typical number of resonances that is in near-quantitative agreement with experiment. We show that the main coupling mechanism results from spin-rotation and spin-spin couplings in combination with the anisotropic atom-molecule interaction. The calculations furthermore explain the qualitative difference between the numbers of resonances in either spin state.