Quantum dynamics in strong fluctuating fields

TL;DR

This paper reviews a theoretical framework for analyzing quantum transport in systems exposed to strong, fluctuating, and nonequilibrium external fields, highlighting nonlinear phenomena and the breakdown of thermal detailed balance.

Contribution

It introduces a projector operator-based approach to derive quantum master equations for systems under strong external fields, enabling unified analysis of nonequilibrium fluctuations and quantum transport.

Findings

Strong fluctuating fields induce nonlinear quantum phenomena.

Nonequilibrium conditions break thermal detailed balance.

The framework allows studying quantum dynamics beyond equilibrium.

Abstract

A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. Herein, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis the influence of nonequilibrium fluctuations and periodic electrical fields on quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.