Impurity in a Bose-Einstein condensate and the Efimov effect

TL;DR

This paper explores how three-body Efimov physics influences an impurity in a Bose-Einstein condensate, revealing a smooth atom-to-trimer crossover and suggesting experimental observability of Efimov effects in many-body systems.

Contribution

It introduces a variational approach including two Bogoliubov excitations to capture Efimov physics in a BEC impurity system, showing significant effects even at weak interactions.

Findings

Energy and quasiparticle residue are lowered by three-body correlations.

Smooth crossover from atom to Efimov trimer with increasing attraction.

Three-body loss does not prevent experimental observation.

Abstract

We investigate the zero-temperature properties of an impurity particle interacting with a Bose-Einstein condensate (BEC), using a variational wavefunction that includes up to two Bogoliubov excitations of the BEC. This allows one to capture three-body Efimov physics, as well as to recover the first non-trivial terms in the weak-coupling expansion. We show that the energy and quasiparticle residue of the dressed impurity (polaron) are significantly lowered by three-body correlations, even for weak interactions where there is no Efimov trimer state in a vacuum. For increasing attraction between the impurity and the BEC, we observe a smooth crossover from atom to Efimov trimer, with a superposition of states near the Efimov resonance. We furthermore demonstrate that three-body loss does not prohibit the experimental observation of these effects. Our results thus suggest a route to realizing Efimov physics in a stable quantum many-body system for the first time.