Equilibrium states in open quantum systems

TL;DR

This paper investigates the existence and nature of equilibrium states in open quantum systems described by non-Hermitian Hamiltonians, highlighting the effects of exceptional points and external mixing.

Contribution

It demonstrates that equilibrium states can exist in open quantum systems with non-Hermitian Hamiltonians, differing from closed systems, and characterizes their properties.

Findings

Equilibrium states exist in open quantum systems far from exceptional points.

These states have orthogonal wavefunctions despite the non-Hermitian Hamiltonian.

External mixing influences the properties of equilibrium states.

Abstract

The aim of the paper is to study the question whether or not equilibrium states exist in open quantum systems that are embedded in at least two environments and are described by a non-Hermitian Hamilton operator $\cal H$. The eigenfunctions of $\cal H$ contain the influence of exceptional points (EPs) as well as that of external mixing (EM) of the states via the environment. As a result, equilibrium states exist (far from EPs). They are different from those of the corresponding closed system. Their wavefunctions are orthogonal although the Hamiltonian is non-Hermitian.