The three-body parameter for Efimov states in lithium-6

TL;DR

This paper provides a precise analysis of Efimov resonances in lithium-6, refining the three-body parameter measurement and comparing it with other atomic systems, highlighting discrepancies that challenge existing theories.

Contribution

It introduces a finite-temperature model for three distinguishable fermions and offers the most accurate determination of the 3BP in lithium-6 to date.

Findings

The 3BP in lithium-6 differs by ~20% from cesium, challenging universality assumptions.

The analysis yields consistent 3BP values from both ground and excited Efimov states.

The study refines the understanding of three-body interactions in fermionic systems.

Abstract

We present a state-of-the-art reanalysis of experimental results on Efimov resonances in the three-fermion system of $^6$Li. We discuss different definitions of the 3-body parameter (3BP) for Efimov states, and adopt a definition that excludes effects due to deviations from universal scaling for low-lying states. We develop a finite-temperature model for the case of three distinguishable fermions and apply it to the excited-state Efimov resonance to obtain the most accurate determination to date of the 3BP in an atomic three-body system. Our analysis of ground-state Efimov resonances in the same system yields values for the three-body parameter that are consistent with the excited-state result. Recent work has suggested that the reduced 3BP for atomic systems is a near-universal quantity, almost independent of the particular atom involved. However, the value of the 3BP obtained for $^6$Li is significantly ($\sim 20$%) different from that previously obtained from the excited-state resonance in Cs. The difference between these values poses a challenge for theory.