Non-adiabatic couplings as a stabilization mechanism in long-range Rydberg molecules

TL;DR

This paper investigates how non-adiabatic couplings can stabilize long-range Rydberg molecules by creating additional barriers, potentially dominating binding and extending molecular lifetimes beyond traditional quantum reflection mechanisms.

Contribution

It demonstrates that non-adiabatic couplings significantly influence vibrational stability and lifetimes in Rydberg molecules, a factor often overlooked in previous models.

Findings

Non-adiabatic couplings can stabilize vibrational states against predissociation.

These couplings can dominate binding, extending molecular lifetimes.

Molecular lifetimes can reach the atomic Rydberg lifetime due to non-adiabatic effects.

Abstract

Long-range Rydberg molecules are typically bound in wells formed in their oscillatory potential energy curves. In alkaline Rydberg molecules, bound vibrational states exist even when these potential wells are disrupted by level repulsion from the steep butterfly potential energy curve induced by a scattering shape resonance. The binding in this case is attributed to quantum reflection. However, the rapidly varying regions of the potential energy landscape where quantum reflection occurs often coincide with regions where non-adiabatic coupling becomes significant. By comparing the molecular states calculated within the Born-Oppenheimer approximation, where quantum reflection is the only binding mechanism, with those obtained from the full set of coupled channel equations, we can assess the effects of non-adiabatic coupling on vibrational energies and lifetimes. Our findings show that these couplings can stabilize the molecule by providing an additional barrier which protects the vibrational states from predissociation and non-radiative transitions. There can also be extreme cases where non-adiabatic coupling completely dominates the binding and the molecular lifetimes saturate at the atomic Rydberg lifetime.