Local approach to entropy production in the nonequilibrium dynamics of open quantum systems

TL;DR

This paper investigates the local entropy production rate in open quantum systems, linking its positivity to Markovianity and spectral properties of the dynamics, and clarifies its relation to non-Markovian behavior.

Contribution

It establishes a connection between entropy production positivity, spectral properties, and Markovianity, and provides counterexamples to previous assumptions about non-Markovian dynamics.

Findings

Positivity of entropy production implies negative real parts of eigenvalues.

Markovian dynamics ensure positive entropy production rate.

Non-Markovian dynamics can still have positive entropy production.

Abstract

We discuss fundamental features of the local expression for the entropy production rate of the nonequilibrium quantum dynamics of open systems and its relations to memory effects and the spectrum of the generator of the dynamics. Defining the entropy production rate as negative rate of change of the relative entropy with respect to an instantaneous fixed point, it is shown that positivity of the entropy production rate for all possible initial states implies that the real parts of the eigenvalues of the time-local generator for the quantum master equation are always negative. It is further demonstrated that Markovian dynamics, identified as P-divisibility of the quantum dynamical map, implies positivity of entropy production rate, thus providing a kind of generalized second law in the nonequilibrium regime. We also prove by means of the counterexample of a phase covariant quantum master equation that the converse of this statement is not true, i.e., there are non-Markovian dynamics for which the entropy production rate is always positive. Thus, we conclude that the emergence of negative entropy production rates is a sufficient but not necessary condition for non-Markovianity of the quantum dynamics. Finally, we also consider a recently introduced map-based notion of entropy production and show the equivalence between its positivity and Markovianity for general finite-dimensional systems.