Universal properties in ultracold ion-atom interactions

TL;DR

This paper develops a quantum-defect theory for ion-atom interactions with long-range $-1/r^4$ potentials, revealing universal bound and resonance spectra, and proposing new methods for spectroscopic measurements and molecular predictions.

Contribution

It introduces a novel quantum-defect framework for universal properties in ion-atom interactions, including bound states, resonances, and molecular formations.

Findings

Universal bound spectrum analogous to Rydberg formula

Universal resonance spectrum for ion-atom scattering

Method for precise atomic polarizability measurement

Abstract

We present some of the universal properties in ion-atom interaction derived from a newly formulated quantum-defect theory for $-1/r^4$ type of long-range interactions. For bound states, we present the universal bound spectrum, namely the equivalent of the Rydberg formula, for ion-atom systems. For scattering, we introduce the concept of universal resonance spectrum to give a systematic understanding of many resonances present in ion-atom scattering. The theory further provides a method for an accurate spectroscopic determination of the atomic polarizability. It also suggests the existence of atom-like molecules, in which multiple atoms orbit around a heavy ion.