Characterizing quasibound states and scattering resonances

TL;DR

This paper introduces an automated method for identifying and characterizing quasibound states and scattering resonances in quantum scattering calculations, improving efficiency and accuracy over manual techniques.

Contribution

The authors develop a reliable, automated procedure based on phase shifts and S-matrix eigenphase sums for extracting quasibound state properties in both single- and multichannel scattering.

Findings

Successfully applied to narrow Van der Waals complex Ar--H$_2$

Analyzed near-threshold states of $^{85}$Rb$_2$ with variable lifetimes

Provides energy, width, phase shift, and partial decay widths of resonances

Abstract

Characterizing quasibound states from coupled-channel scattering calculations can be a laborious task, involving extensive manual iteration and fitting. We present an automated procedure, based on the phase shift or S-matrix eigenphase sum, that reliably converges on a quasibound state (or scattering resonance) from some distance away. It may be used for both single-channel and multichannel scattering. It produces the energy and width of the state and the phase shift of the background scattering, and hence the lifetime of the state. It also allows extraction of partial widths for decay to individual open channels. We demonstrate the method on a very narrow state in the Van der Waals complex Ar--H$_2$, which decays only by vibrational predissociation, and on near-threshold states of $^{85}$Rb$_2$, whose lifetime varies over 4 orders of magnitude as a function of magnetic field.