Keldysh Field Theory for Driven Open Quantum Systems

TL;DR

This paper reviews recent advances in the theoretical understanding of driven open quantum systems, emphasizing the Keldysh field theory approach to analyze their non-equilibrium dynamics and emergent phenomena.

Contribution

It introduces the open system Keldysh functional integral method, merging quantum optics and many-body physics for driven dissipative systems.

Findings

Identification of universal non-equilibrium phenomena

Development of the Keldysh functional integral framework

Insights into non-thermal steady states

Abstract

Recent experimental developments in diverse areas - ranging from cold atomic gases over light-driven semiconductors to microcavity arrays - move systems into the focus, which are located on the interface of quantum optics, many-body physics and statistical mechanics. They share in common that coherent and driven-dissipative quantum dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in condensed matter. This concerns both their non-thermal flux equilibrium states, as well as their many-body time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and many-body physics, and leverages the power of modern quantum field theory to driven open quantum systems.