Transient fluctuation relations for time-dependent particle transport

TL;DR

This paper develops a stochastic path integral framework to derive fluctuation relations for time-dependent particle transport, bridging classical and quantum descriptions, and applies it to mesoscopic systems.

Contribution

It introduces a novel stochastic path integral approach to derive fluctuation relations in time-dependent particle transport, incorporating quantum effects in a classical limit.

Findings

Derived general functional fluctuation relations for current flow.

Showed that measurement processes do not invalidate quantum fluctuation relations.

Applied reduced relations to mesoscopic transport examples.

Abstract

We consider particle transport under the influence of time-varying driving forces, where fluctuation relations connect the statistics of pairs of time reversed evolutions of physical observables. In many "mesoscopic" transport processes, the effective many-particle dynamics is dominantly classical, while the microscopic rates governing particle motion are of quantum-mechanical origin. We here employ the stochastic path integral approach as an optimal tool to probe the fluctuation statistics in such applications. Describing the classical limit of the Keldysh quantum nonequilibrium field theory, the stochastic path integral encapsulates the quantum origin of microscopic particle exchange rates. Dynamically, it is equivalent to a transport master equation which is a formalism general enough to describe many applications of practical interest. We apply the stochastic path integral to derive general functional fluctuation relations for current flow induced by time-varying forces. We show that the successive measurement processes implied by this setup do not put the derivation of quantum fluctuation relations in jeopardy. While in many cases the fluctuation relation for a full time-dependent current profile may contain excessive information, we formulate a number of reduced relations, and demonstrate their application to mesoscopic transport. Examples include the distribution of transmitted charge, where we show that the derivation of a fluctuation relation requires the combined monitoring of the statistics of charge and work.