Quantum anomaly, non-Hermitian skin effects, and entanglement entropy in open systems

TL;DR

This paper explores the interplay of non-Hermitian topology, spectral properties, and entanglement in open quantum systems, revealing how topological defects influence skin effects and steady states with potential applications in quantum transport.

Contribution

It provides a unified understanding of non-Hermitian topology's role in spectral and entanglement properties, linking topological defects to skin effects and steady states in open systems.

Findings

Higher-dimensional skin effects require topological defects.

Steady states relate to Majorana modes and chiral edge states.

Entanglement entropy reveals nonreciprocal currents and skin-effect voltages.

Abstract

We investigate the roles of non-Hermitian topology in spectral properties and entanglement structures of open systems. In terms of spectral theory, we give a unified understanding of two interpretations of non-Hermitian topology: quantum anomaly and non-Hermitian skin effects, in which the bulk spectra extremely depend on the boundary conditions. In this context, the fact that the intrinsic higher-dimensional skin effects under the full open boundary condition need the presence of the topological defects is understood in terms of the anomalous fermion production such as the Rubakov-Callan effect in the presence of the magnetic monopole. In terms of the entanglement structure, we investigate steady states of fermionic open systems whose Liouvillian (rapidity) spectra host non-Hermitian topology. We analyze dissipation-driven Majorana steady states in zero-dimensional open systems and relate them to the Majorana edge modes of topological superconductors by using the entanglement entropy. We also analyze a steady state of a one-dimensional open Fermi system with a non-Hermitian topological spectrum and relate it to the chiral edge states of the Chern insulator on the basis of the trace index defined from the entanglement spectrum. These correspondences indicate that the entanglement generates circular nonreciprocal currents under the periodic boundary condition and the skin-effect voltage with fermion accumulation under the open boundary condition. Finally, we discuss several related topics such as pseudospectral behaviors of Liouvillian dynamics and skin effects in interacting systems.