Testing the universality of three-body interactions near narrow Feshbach resonances*

The interplay between the length-scales describing the short-range, exchange, and the van der Waals interaction across a series of alkali-metal, homonuclear samples is likely an important factor determining the universal behavior of the Efimov spectrum [1]. Thus, we aim to study properties of Efimov states and explore their dependence on the strength of the underlying Feshbach resonance. Within a two-channel model for the interatomic interactions, we calculate the energies of the Efimov ground and exited states to test the van der Waals universality expected for strong (broad) Feshbach resonances. By varying the position and strength of the two-body coupling between the channels, we modify the strength/width of the Feshbach resonance, as measured by the ‘sres’ parameter [2]. Investigating across a range of Feshbach resonance widths, we showcase the appearance of non-universal behavior of the Efimov trimer in the ground and excited states, likely emergent from a repulsive interaction in the atom-dimer channel, which appears for narrow resonances [3]. We discuss physical properties of the resonance that determine the lifetime and energy of Efimov states in the narrow-resonance regime.

[1] Precision Test of the Limits to Universality in Few-Body Physics. R. Chapurin, X. Xie, M. J. Van de Graaff, J. S. Popowski, J. P. D’Incao, P. S. Julienne, J. Ye, and E. A. Cornell - Phys. Rev. Lett. 123, 233402, (2019)

[2] Feshbach resonances in ultracold gases. C. Chin, R. Grimm, P. S. Julienne, E. Tiesinga - Rev. Mod. Phys. 82, 1225 (2010)

[3] Reshaped three-body interactions and the observation of an Efimov state in the continuum. Y.Yudkin, R. Elbaz, J. P. D'Incao, P. S. Julienne, L. Khaykovich – Nat. Comm. 15, 2127 (2024)