Spin-orbit-dependent lifetimes of long-range Rydberg molecules

TL;DR

This study combines theory and experiment to analyze spin-orbit effects on the lifetimes of long-range Rydberg molecules in cesium, revealing how spin-orbit interactions influence decay channels and molecular stability.

Contribution

It introduces a relativistic model including spin-orbit coupling and hyperfine structure, and experimentally measures lifetimes of inner and outer well Rydberg molecules, linking spin-orbit effects to molecular decay.

Findings

Inner-well lifetimes increase with detuning and match calculations.

Autoionisation is confirmed as the main decay channel.

Spin-orbit interactions significantly reduce molecular lifetimes.

Abstract

Long-range Rydberg molecules (LRMs) form when a highly excited Rydberg electron scatters from ground-state atoms inside its orbit, creating oscillatory, long-range potentials. We present a combined theoretical and experimental study of caesium dimers correlated to 402P3/2 Rydberg states, with an emphasis on decay via autoionisation (associative ionisation). Our model includes a relativistic treatment of electron-atom scattering with spin-orbit coupling, the perturber's hyperfine structure, and coupling of vibrational levels to a continuum of short-range decay channels. Calculated potential-energy curves predict two families of wells: outer wells near the classical outer turning point supporting long-lived states, and inner wells at shorter range whose lifetimes are limited by tunneling and subsequent vibronic decay. Using photoassociation in an ultracold Cs gas and an analysis of pulsed-field-ionisation signals which are highly selective for the detection of molecules, we assign resonances by binding energy and measure lifetimes. The measured lifetimes of inner-well states increase systematically with increasing detuning and agree with calculated lifetimes; detection of Cs2+ product ions supports autoionisation as a dominant channel. We show that the lifetimes are strongly reduced by spin-orbit interactions in the transient Cs-collision complex, which lift the near-degeneracy in Omega observed for states in the outer well and control the inner-well binding. The identified states also provide promising pathways to create ultracold molecules in ion-pair states.