Existence of the thermodynamic limit and asymptotic behavior of some irreversible quantum dynamical systems

TL;DR

This paper investigates the properties of irreversible quantum dynamics in open systems, establishing Lieb-Robinson bounds, thermodynamic limits, and analyzing the asymptotic behavior of photon numbers in cavity QED systems.

Contribution

It proves the existence of the thermodynamic limit for quantum lattice systems with Lindblad generators and analyzes the asymptotic photon behavior in cavity QED models with both ideal and leaky cavities.

Findings

Lieb-Robinson bounds hold for finite and infinite lattice systems.

Photon number diverges in ideal cavities, stabilizes in leaky cavities.

The limiting state in leaky cavities is independent of initial conditions.

Abstract

We discuss the properties of two open quantum systems with a general class of irreversible quantum dynamics. First we study Lieb-Robinson bounds in a quantum lattice systems. The time-dependent generator of the dynamics of the system is of the Lindblad-Kossakowski type. This generator satisfies some suitable decay condition in space. We show that the dynamics with a such generator on a finite system is a well-defined quantum dynamics in a sense of a norm-continuous cocycle of unit preserving completely positive maps. After proving Lieb-Robinson bounds for a finite lattice systems we also show the existence of the thermodynamic limit of the dynamics. We show that in a strong limit there exits a strongly continuous cocycle of unit preserving completely positive maps. Which means that the dynamics exists in an infinite system, where Lieb-Robinson bounds also holds. In the second part of the paper we consider a system that consists of a beam of two-level atoms that pass one by one through the microwave cavity. The atoms are randomly excited and there is exactly one atom present in the cavity at any given moment. We consider both the ideal and leaky cavity and study the time asymptotic behavior of the state of the cavity. We show that the number of photons increases indefinitely in the case of the ideal cavity. In case of leaky cavity we prove that the mean photon number in the cavity stabilizes in time. The limiting state of the cavity in this case exists and it is independent of the initial state. We calculate the characteristic functional of this non-quasi-free non-equilibrium state. We also calculate the energy flux in both the ideal and leaky and the entropy production for the ideal cavity.