Evidence for Efimov quantum states in an ultracold gas of cesium atoms

TL;DR

This paper reports the first experimental observation of Efimov quantum states in an ultracold cesium gas, confirming key theoretical predictions about three-body bound states in quantum physics.

Contribution

It provides the first experimental evidence of Efimov states in ultracold atoms, demonstrating their existence through observed resonances and loss features.

Findings

Observation of an Efimov resonance in cesium atoms

Detection of a minimum in three-body recombination loss

Confirmation of Efimov physics predictions

Abstract

Systems of three interacting particles are notorious for their complex physical behavior. A landmark theoretical result in few-body quantum physics is Efimov's prediction of a universal set of bound trimer states appearing for three identical bosons with a resonant two-body interaction. Counterintuitively, these states even exist in the absence of a corresponding two-body bound state. Since the formulation of Efimov's problem in the context of nuclear physics 35 years ago, it has attracted great interest in many areas of physics. However, the observation of Efimov quantum states has remained an elusive goal. Here we report the observation of an Efimov resonance in an ultracold gas of cesium atoms. The resonance occurs in the range of large negative two-body scattering lengths, arising from the coupling of three free atoms to an Efimov trimer. Experimentally, we observe its signature as a giant three-body recombination loss when the strength of the two-body interaction is varied. We also detect a minimum in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point with which to explore the universal properties of resonantly interacting few-body systems. While Feshbach resonances have provided the key to control quantum-mechanical interactions on the two-body level, Efimov resonances connect ultracold matter to the world of few-body quantum phenomena.