Recent advances in Ultralong-range Rydberg molecules

Abstract

Rydberg molecule, formed by one or more Rydberg atoms, exhibits 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 molecule that is bound via a low-energy electron-atom scattering interaction between ground atom and Rydberg electron, the Rydberg-Rydberg molecule that is bound via a long-range electrostatic interaction between Rydberg atoms, and the ion-Rydberg molecule that is bound via single- or multi-polar interactions between Rydberg atom and 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.

Figures (17)

• Figure 1: Different molecule types. Molecules in nature are mainly bound by ionic bonds, covalent bonds and metallic bonds. The new type of long-range Rydberg molecules can be divided into three categories, ground-Rydberg molecules, Rydberg macrodimer, and ion-Rydberg molecules.
• Figure 2: Model of a ground-Rydberg molecule formed by two Cs atoms in the ground-state and Rydberg state.
• Figure 3: Potential energy curves of the Cs molecule near $n = 19$. The inset shows the "trilobite-type" ("butterfly-type") molecular electron probability density that is formed in the potential wells at the purple (orange) origin markers I (II) BaisyPhD2021.
• Figure 4: (a) Measured spectra of $35S, 36S$ and $37S$ Rb ground-Rydberg molecules. The right overview is centered on the atomic Rydberg transition. The left side shows the higher resolution molecular lines for $\nu=0,1$ bound state. Diamonds mark the peaks that have not yet been assigned. (b) Stark map of the atomic $35S$ state and the molecular $^3\Sigma(5S–35S)~(\nu=0)$ state, showing an obvious quadratic Stark effect (white lines) Bendkowsky2009. (Reproduced with permission and adapted from Ref. Bendkowsky2009, licensed under a Creative Commons Attribution 4.0 International license.)
• Figure 5: (a) Level diagram for the two-photon excitation scheme. (b) Comparison between the calculated PEC and measured photo-association spectroscopy of Cs ground-Rydberg molecules. Different vibrational levels marked by the dashed lines are clearly distinguishable, and even-parity $(\nu= 0, 2, ..)$ vibrational levels have stronger signals. (c) Linewidth as a function of electric field for the red wavefunction-marked vibrational states in (b), yielding a permanent dipole moment of 2,330(400) Debye booth2015. (Reproduced with permission and adapted from Ref. booth2015, licensed under a Creative Commons Attribution 4.0 International license.)