Observation of Feshbach resonances between alkali and closed-shell atoms

TL;DR

This paper reports the first observation of magnetic Feshbach resonances between alkali and closed-shell atoms, enabling new control over ultracold molecules and advancing quantum many-body research.

Contribution

It provides the first experimental evidence of narrow Feshbach resonances in alkali-closed-shell atom systems, specifically Rb and Sr, which were previously predicted but not observed.

Findings

First observation of Feshbach resonances in Rb-Sr system

Resonances enable creation of ultracold polar molecules

Paves the way for new quantum many-body experiments

Abstract

Magnetic Feshbach resonances are an invaluable tool for controlling ultracold atoms and molecules. They can be used to tune atomic interactions and have been used extensively to explore few- and many-body phenomena. They can also be used for magnetoassociation, in which pairs of atoms are converted into molecules by ramping an applied magnetic field across a resonance. Pairs of open-shell atoms, such as the alkalis, chromium, and some lanthanides, exhibit broad resonances because the corresponding molecule has multiple electronic states. However, molecules formed between alkali and closed-shell atoms have only one electronic state and no broad resonances. Narrow resonances have been predicted in such systems, but until now have eluded observation. Here we present the first observation of magnetic Feshbach resonances in a system containing a closed-shell atom, Sr, interacting with an alkali atom, Rb. These resonances pave the way to creating an ultracold gas of strongly polar, open-shell molecules, which will open up new possibilities for designing quantum many-body systems and for tests of fundamental symmetries.