Berry Phase of a Resonant State

TL;DR

This paper derives analytical formulas for the complex Berry phase in open quantum systems with resonant states, revealing unique degeneracy geometries and topological features distinct from bound states.

Contribution

It introduces new analytical expressions for the Berry phase in resonant states and explores their geometric and topological implications in open quantum systems.

Findings

Resonant state degeneracies form continuous lines of singularities.

The geometric phase exhibits topologically distinct classes of closed paths.

Resonant states show dilation effects linked to the imaginary part of the Berry phase.

Abstract

We derive closed analytical expressions for the complex Berry phase of an open quantum system in a state which is a superposition of resonant states and evolves irreversibly due to the spontaneous decay of the metastable states. The codimension of an accidental degeneracy of resonances and the geometry of the energy hypersurfaces close to a crossing of resonances differ significantly from those of bound states. We discuss some of the consequences of these differences for the geometric phase factors, such as: Instead of a diabolical point singularity there is a continuous closed line of singularities formally equivalent to a continuous distribution of `magnetic' charge on a diabolical circle; different classes of topologically inequivalent non-trivial closed paths in parameter space, the topological invariant associated to the sum of the geometric phases, dilations of the wave function due to the imaginary part of the Berry phase and others.