Long-range Rydberg molecules, Rydberg macrodimers and Rydberg aggregates in an ultracold Cs gas

TL;DR

This paper reviews recent studies on long-range interactions in ultracold Cs Rydberg gases, focusing on molecular resonances, interaction modeling, and excitation phenomena, revealing new insights into Rydberg molecule formation and dynamics.

Contribution

It introduces detailed experimental and theoretical analysis of two types of long-range Rydberg molecular resonances in ultracold Cs gases, including a novel autocatalytic antiblockade effect.

Findings

Identification of two types of molecular resonances.

Modeling of interaction potentials using multipole expansion and Fermi-contact pseudo-potential.

Observation of a saturable autocatalytic antiblockade phenomenon.

Abstract

We present an overview of our recent investigations of long-range interactions in an ultracold Cs Rydberg gas. These interactions are studied by high-resolution photoassociation spectroscopy, using excitation close to one-photon transitions into $n$p$_{3/2}$ Rydberg states with pulsed and continuous-wave ultraviolet laser radiation, and lead to the formation of long-range Cs$_2$ molecules. We observe two types of molecular resonances. The first type originates from the correlated excitation of two atoms into Rydberg-atom-pair states interacting at long range via multipole-multipole interactions. The second type results from the interaction of one atom excited to a Rydberg state with one atom in the electronic ground state. Which type of resonances is observed in the experiments depends on the laser intensity and frequency and on the pulse sequences used to prepare the Rydberg states. We obtain insights into both types of molecular resonances by modelling the interaction potentials, using a multipole expansion of the long-range interaction for the first type of resonances and a Fermi-contact pseudo-potential for the second type of resonances. We analyse the relation of these long-range molecular resonances to molecular Rydberg states and ion-pair states, and discuss their decay channels into atomic and molecular ions. In experiments carried out with a two-colour two-photon excitation scheme, we observe a large enhancement of Rydberg-excitation probability, which we interpret as a saturable autocatalytic antiblockade phenomenon.