Loosely Bound Few-Body States in a Spin-1 Gas with Near-Degenerate Continua

TL;DR

This paper investigates how near-degenerate two-body continua influence few-body states in ultracold lithium gases near a narrow Feshbach resonance, revealing unique Efimov trimer behaviors and clarifying the role of interaction potential details.

Contribution

It introduces a three-channel model with two atomic continua to analyze the impact of near-degenerate continua on few-body physics, extending previous molecular-channel models.

Findings

Efimov trimer energies follow a different functional form with two continua.

Threshold energies remain unchanged despite the continua.

Short-range interaction details likely cause exotic Efimov behavior.

Abstract

A distinguishing feature of ultracold collisions of bosonic lithium atoms is the presence of two near-degenerate two-body continua. The influence of such a near-degeneracy on the few-body physics in the vicinity of a narrow Feshbach resonance is investigated within the framework of a minimal model with two atomic continua and one closed molecular channel. The model allows analysis of the spin composition of loosely bound dimers and trimers. In the two-body sector the well-established coupled-channels calculations phenomenology of lithium is qualitatively reproduced, and its particularities are emphasized and clarified. In the three-body sector we find that the Efimov trimer energy levels follow a different functional form as compared to a single continuum scenario while the thresholds remain untouched. This three-channel model with two atomic continua complements our earlier developed three-channel model with two molecular channels [Y. Yudkin and L. Khaykovich, Phys. Rev. A 103, 063303 (2021)] and suggests that the experimentally observed exotic behavior of the first excited Efimov energy level [Y. Yudkin, R. Elbaz and L. Khaykovich, arXiv:2004.02723] is most probably caused by the short-range details of the interaction potential.