Observation of a Halo Trimer in an Ultracold Bose-Fermi Mixture

TL;DR

This paper reports the discovery of a new halo trimer state in an ultracold mixture of sodium and potassium atoms, revealing universal three-body phenomena and providing insights into many-body physics and molecule formation.

Contribution

It presents the first observation of a halo trimer involving two bosons and one fermion in an ultracold mixture, expanding understanding of universal three-body states.

Findings

Halo trimer closely follows dimer resonance across interaction strengths.

The trimer's structure is a Feshbach dimer weakly bound to an additional boson.

Theoretical analysis reproduces experimental observations.

Abstract

The quantum mechanics of three interacting particles gives rise to interesting universal phenomena, such as the staircase of Efimov trimers predicted in the context of nuclear physics and observed in ultracold gases. Here, we observe a novel type of halo trimer using radiofrequency spectroscopy in an ultracold mixture of $^{23}$Na and $^{40}$K atoms. The trimers consist of two light bosons and one heavy fermion, and have the structure of a Feshbach dimer weakly bound to one additional boson. We find that the trimer peak closely follows the dimer resonance over the entire range of explored interaction strengths across an order of magnitude variation of the dimer energy, as reproduced by our theoretical analysis. The presence of this halo trimer is of direct relevance for many-body physics in ultracold mixtures and the association of ultracold molecules.