Asymmetric lineshapes of Efimov resonances in mass-imbalanced ultracold gases

TL;DR

This paper investigates the asymmetric lineshapes of Efimov resonances in mass-imbalanced ultracold gases, revealing how interference effects and scattering length variations influence resonance profiles and widths.

Contribution

It introduces a semi-classical approach combined with hyperspherical representation to quantify Efimov resonance asymmetries using Fano profiles and derives a closed-form expression for resonance width and asymmetry.

Findings

Efimov resonances display asymmetric Fano lineshapes due to interference effects.

A closed-form expression relates resonance width and Fano asymmetry parameter.

Resonance profiles exhibit a $q$-reversal effect with varying scattering lengths.

Abstract

The resonant profile of the rate coefficient for three-body recombination into a shallow dimer is investigated for mass-imbalanced systems. In the low-energy limit, three atoms collide with zero-range interactions, in a regime where the scattering lengths of the heavy-heavy and the heavy-light subsystems are positive and negative, respectively. For this physical system, the adiabatic hyperspherical representation is combined with a fully semi-classical method and we show that the shallow dimer recombination spectra display an asymmetric lineshape that originates from the coexistence of Efimov resonances with St\"uckelberg interference minima. These asymmetric lineshapes are quantified utilizing the Fano profile formula. In particular, a closed form expression is derived that describes the width of the corresponding Efimov resonances and the Fano lineshape asymmetry parameter $q$. The profile of Efimov resonances exhibits a $q-$reversal effect as the inter- and intra-species scattering lengths vary. In the case of a diverging asymmetry parameter, i.e. $|q|\to \infty$, we show that the Efimov resonances possess zero width and are fully decoupled from the three-body and atom-dimer continua, and the corresponding Efimov metastable states behave as bound levels.