Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture

TL;DR

This study observes Efimov resonances in an ultracold Li-Cs mixture at very low temperatures, confirming universal theory predictions for excited states and revealing deviations for the ground state, with implications for understanding three-body interactions.

Contribution

It reports the first observation of the second excited Efimov resonance in a mass-imbalanced mixture at ultracold temperatures, extending previous results and testing universal theories.

Findings

First and second excited Efimov resonances observed in Li-Cs mixture.

Good agreement with universal zero-range theory for excited states.

Deviations observed for the Efimov ground state and larger inelasticity parameter.

Abstract

We study Efimov resonances via three-body loss in an ultracold two-component gas of fermionic $^6$Li and bosonic $^{133}$Cs atoms close to a Feshbach resonance at 843~G, extending results reported previously [Pires \textit{et al.}, Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120~nK. The experimental scheme for reaching lower temperatures is based upon compensating the gravity-induced spatial separation of the mass-imbalanced gases with bichromatic optical dipole traps. We observe the first and second excited Li-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body event rate constant, in good agreement with the universal zero-range theory at finite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)]. Deviations are found for the Efimov ground state, and the inelasticity parameter $\eta$ is found to be significantly larger than those for single-species systems.