Ultralong-range Rydberg molecules in cold atom gases

Rydberg molecules, formed by one or more Rydberg atoms, exhibit remarkable properties, including an exceptionally large spatial extent, rich rovibrational level structures, permanent electric dipole moments, and a pronounced sensitivity to external fields. Based on the underlying binding mechanisms, Rydberg molecules can be divided into three categories: the ground-Rydberg molecules that are bound via a low-energy electron-atom scattering interaction between a ground atom and a Rydberg electron, the Rydberg-Rydberg molecules that are bound via a long-range electrostatic interaction between Rydberg atoms, and the ion-Rydberg molecules that are bound via single- or multi-polar interactions between a Rydberg atom and an ion. This review focuses on recent theoretical and experimental advances in diatomic Rydberg molecules, covering their formation and binding mechanisms, potential energy curves, experimental observations, and spectroscopic properties, with the aim of providing a comprehensive overview of the current state and future prospects of this rapidly developing field.