Electronic phase coherence versus dissipation in solid-state quantum devices: Two approximations are better than one

TL;DR

This paper compares non-Markovian and Markovian density-matrix approaches in modeling quantum nanodevices, highlighting that combining approximations yields more physically accurate results, especially in zero-dimensional systems with phonon interactions.

Contribution

It demonstrates that combining adiabatic and mean-field approximations improves the physical reliability of quantum device simulations.

Findings

Non-Markovian mean-field can produce unphysical results.

Markovian approach with combined approximations ensures physical solutions.

Two approximations together outperform single methods.

Abstract

In the microscopic modeling of new-generation electronic quantum nanodevices a variety of simulation strategies have been proposed and employed. Aim of this Letter is to point out virtues versus intrinsic limitations of non-Markovian density-matrix approaches; we shall show that the usual mean-field treatment may lead to highly unphysical results, like negative distribution probabilities and non-dissipative behaviours, which are particularly severe in zero-dimensional electronic systems coupled to dispersionless phonon modes. This is in striking contrast with Markovian treatments, where a proper combination of adiabatic limit and mean-field schemes guarantees a physically acceptable solution; as a result, the unusual conclusion is that two approximations are better than one.