Universality in Three- and Four-Body Bound States of Ultracold Atoms

TL;DR

This paper experimentally investigates universal properties of three- and four-body bound states, known as Efimov trimers, in ultracold lithium atoms, confirming theoretical predictions and observing deviations near resonance.

Contribution

It provides experimental evidence for universal Efimov trimers and four-body states in ultracold atoms, with precise measurements across a Feshbach resonance.

Findings

Identification of two Efimov trimers and associated four-body states

Agreement of relative positions with universal theory away from resonance

Systematic deviations from universality across the resonance

Abstract

Under certain circumstances, three or more interacting particles may form bound states. While the general few-body problem is not analytically solvable, the so-called Efimov trimers appear for a system of three particles with resonant two-body interactions. The binding energies of these trimers are predicted to be universally connected to each other, independent of the microscopic details of the interaction. By exploiting a Feshbach resonance to widely tune the interactions between trapped ultracold lithium atoms, we find evidence for two universally connected Efimov trimers and their associated four-body bound states. A total of eleven precisely determined three- and four-body features are found in the inelastic loss spectrum. Their relative locations on either side of the resonance agree well with universal theory, while a systematic deviation from universality is found when comparing features across the resonance.