Observation of an Efimov spectrum in an atomic system

TL;DR

This paper reports the first experimental observation of an Efimov spectrum in an ultracold atomic system, confirming theoretical predictions about universal three-body bound states.

Contribution

It provides the first direct evidence of Efimov trimer states in an atomic system, validating the universal scaling laws predicted by Efimov's theory.

Findings

Discovery of two Efimov-related trimer states in potassium atoms

Observation of the characteristic geometric energy scaling

Validation of Efimov's universal three-body physics

Abstract

In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is still of great interest today. He found that three particles subjected to a resonant pairwise interaction can join into an infinite number of loosely bound states even though each particle pair cannot bind. Interestingly, the properties of these aggregates, such as the peculiar geometric scaling of their energy spectrum, are universal, i.e. independent of the microscopic details of their components. Despite an extensive search in many different physical systems, including atoms, molecules and nuclei, the characteristic spectrum of Efimov trimer states still eludes observation. Here we report on the discovery of two bound trimer states of potassium atoms very close to the Efimov scenario, which we reveal by studying three-particle collisions in an ultracold gas. Our observation provides the first evidence of an Efimov spectrum and allows a direct test of its scaling behaviour, shedding new light onto the physics of few-body systems.