Molecular Heat Engines: Quantum Coherence Effects

TL;DR

This paper investigates how quantum coherence influences the efficiency of molecular heat engines, revealing that coherence can enhance performance but is sensitive to dephasing and dissipation effects.

Contribution

It introduces a nonequilibrium Green function approach to analyze quantum coherence effects in molecular thermoelectric devices, surpassing traditional rate equation models.

Findings

Quantum coherence can boost thermoelectric efficiency.

Dephasing and dissipation negate coherence benefits.

Green function method captures quantum effects accurately.

Abstract

Recent developments in nanoscale experimental techniques made it possible to utilize single molecule junctions as devices for electronics and energy transfer with quantum coherence playing an important role in their thermoelectric characteristics. Theoretical studies on the efficiency of nanoscale devices usually employ rate (Pauli) equations, which do not account for quantum coherence. Therefore, the question whether quantum coherence could improve the efficiency of a molecular device cannot be fully addressed within such considerations. Here, we employ a nonequilibrium Green function approach to study the effects of quantum coherence and dephasing on the thermoelectric performance of molecular heat engines. Within a generic bichromophoric donor-bridge-acceptor junction model, we show that quantum coherence may increase efficiency compared to quasi-classical (rate equation) predictions and that pure dephasing and dissipation destroy this effect.