Developments in atomic control using ultracold magnetic lanthanides

The detailed structure of each atomic species determines what physics can be achieved with ultracold gases. This review discusses the exciting applications that follow from lanthanides' complex electronic structure. Lanthanide atoms have an unusual electron configuration, with a partially filled shell of f orbitals. This leads to a set of characteristic properties, including 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, that enable enhanced control over ultracold atoms and their interactions. These features, in turn, enable new forms of control as well as novel many-body phenomena. Microkelvin temperatures can be reached by narrow-line laser cooling and evaporative cooling through universal dipolar scattering. The properties and tunability of the interatomic interactions have enabled observations of a rotonic dispersion relation, self-bound liquid-like droplets stabilized by quantum fluctuations and supersolid states. Here 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.

Automated summary

The complex electronic structure of lanthanide atoms leads to multiple characteristic properties, such as a large number of optical transitions, anisotropic interaction properties, and a large magnetic moment and spin space in the ground state. These features enable enhanced control over ultracold atoms and their interactions, leading to new forms of control and novel many-body phenomena.