New opportunites for interactions and control with ultracold lanthanides

TL;DR

This paper reviews how the unique electronic structure of lanthanide atoms enables advanced control and novel quantum phenomena in ultracold atomic systems, highlighting recent experimental progress.

Contribution

It provides a comprehensive overview of the properties of lanthanide atoms and their applications in ultracold physics, emphasizing recent experimental developments.

Findings

Lanthanide atoms exhibit large numbers of optical transitions.

Anisotropic interactions enable new control methods.

Experimental progress includes realization of quantum droplets and supersolids.

Abstract

Lanthanide atoms have an unusual electron configuration, with a partially filled shell of $f$ orbitals. This leads to a set of characteristic properties that enable enhanced control over ultracold atoms and their interactions: large numbers of optical transitions with widely varying wavelengths and transition strengths, anisotropic interaction properties between atoms and with light, and a large magnetic moment and spin space present in the ground state. These features in turn enable applications ranging from narrow-line laser cooling and spin manipulation to evaporative cooling through universal dipolar scattering, to the observation of a rotonic dispersion relation, self-bound liquid-like droplets stabilized by quantum fluctuations, and supersolid states. In this short review, we describe how the unusual level structure of lanthanide atoms leads to these key features, and provide a brief and necessarily partial overview of experimental progress in this rapidly developing field.