Fermionic reaction coordinates and their application to an autonomous Maxwell demon in the strong coupling regime

TL;DR

This paper introduces a fermionic reaction coordinate method that surpasses weak coupling and Markovian limits, enabling analysis of strongly coupled quantum impurity systems and their role in autonomous Maxwell demons.

Contribution

It develops a novel fermionic reaction coordinate mapping that accurately models strong system-bath coupling and non-Markovian effects in quantum impurity systems.

Findings

The method works beyond weak coupling and Markovian approximations.

Maxwell demon behavior diminishes in strong coupling and non-Markovian regimes.

Narrow parameter regimes allow the Maxwell demon to operate effectively.

Abstract

We establish a theoretical method which goes beyond the weak coupling and Markovian approximations while remaining intuitive, using a quantum master equation in a larger Hilbert space. The method is applicable to all impurity Hamiltonians tunnel-coupled to one (or multiple) baths of free fermions. The accuracy of the method is in principle not limited by the system-bath coupling strength, but rather by the shape of the spectral density and it is especially suited to study situations far away from the wide-band limit. In analogy to the bosonic case, we call it the fermionic reaction coordinate mapping. As an application we consider a thermoelectric device made of two Coulomb-coupled quantum dots. We pay particular attention to the regime where this device operates as an autonomous Maxwell demon shoveling electrons against the voltage bias thanks to information. Contrary to previous studies we do not rely on a Markovian weak coupling description. Our numerical findings reveal that in the regime of strong coupling and non-Markovianity, the Maxwell demon is often doomed to disappear except in a narrow parameter regime of small power output.