Dissipative dynamics of atomic and molecular Rydberg gases: Avalanche to ultracold plasma states of strong coupling

TL;DR

This paper reviews the formation and evolution of ultracold plasmas from Rydberg gases, highlighting novel long-lived molecular plasma states with unusual properties that challenge traditional plasma physics understanding.

Contribution

It provides a comprehensive overview of experimental observations of atomic and molecular Rydberg gases evolving into ultracold plasmas, emphasizing unique long-lived molecular plasma phenomena.

Findings

Long-lived molecular ultracold plasma states observed

Anomalously low electron temperatures in molecular plasma

Evidence of phenomena beyond conventional plasma physics

Abstract

Not long after metastable xenon was photoionized in a magneto-optical trap, groups in Europe and North America found that similar states of ionized gas evolved spontaneously from state-selected, high principal quantum number Rydberg gases. Studies of atomic xenon and molecular nitric oxide entrained in a supersonically cooled molecular beam subsequently showed much the same final state evolved from a sequence of prompt Penning ionization and electron-impact avalanche to plasma, well-described by coupled rate-equation simulations. But, measured over longer times, the molecular ultracold plasma was found to exhibit an anomalous combination of very long lifetime and very low apparent electron temperature. This review summarizes early developments in the study of ultracold plasmas formed by atomic and molecular Rydberg gases, and then details observations as they combine to characterize properties of the nitric oxide molecular ultracold plasma that appear to call for an explanation beyond the realm of conventional plasma physics.