Observation of the Efimov state of the helium trimer

TL;DR

This paper reports the first experimental observation of the Efimov state in a helium trimer, confirming long-standing theoretical predictions about three-body quantum states with large spatial extent.

Contribution

The study provides direct experimental evidence of the Efimov state in helium trimers using Coulomb explosion imaging, a significant advancement in quantum few-body physics.

Findings

First direct imaging of an Efimov state in helium trimers

Confirmation of the predicted size and structure of the Efimov state

Observation of a three-body bound state without external tuning

Abstract

Quantum theory dictates that upon weakening the two-body interaction in a three-body system, an infinite number of three-body bound states of a huge spatial extent emerge just before these three-body states become unbound. Three helium atoms have been predicted to form a molecular system that manifests this peculiarity under natural conditions without artificial tuning of the attraction between particles by an external field. Here we report experimental observation of this long predicted but experimentally elusive Efimov state of $^{4}$He$_{3}$ by means of Coulomb explosion imaging. We show spatial images of an Efimov state, confirming the predicted size and a typical structure where two atoms are close to each other while the third is far away.