Effects of system-bath entanglement on the performance of light-harvesting systems: A quantum heat engine perspective

TL;DR

This paper models a three-level quantum system as a heat engine to analyze how system-bath entanglement influences energy transfer efficiency in light-harvesting, revealing that phonon bath coupling can enhance coherence and efficiency.

Contribution

It introduces a polaron-transformed master equation approach to study non-equilibrium quantum energy transfer, highlighting the role of system-bath entanglement in optimizing efficiency.

Findings

Phonon bath coupling induces steady state coherence.

Steady state coherence enhances energy transfer flux.

Efficiency approaches classical heat engine limit at strong coupling.

Abstract

We explore energy transfer in a generic three-level system, which is coupled to three non-equilibrium baths. Built on the concept of quantum heat engine, our three-level model describes non-equilibrium quantum processes including light-harvesting energy transfer, nano-scale heat transfer, photo-induced isomerization, and photovoltaics in double quantum-dots. In the context of light-harvesting, the excitation energy is first pumped up by sunlight, then is transferred via two excited states which are coupled to a phonon bath, and finally decays to the ground state. The efficiency of this process is evaluated by steady state analysis via a polaron-transformed master equation; thus a wide range of the system-phonon coupling strength can be covered. We show that the coupling with the phonon bath not only modifies the steady state, resulting in population inversion, but also introduces a finite steady state coherence which optimizes the energy transfer flux and efficiency. In the strong coupling limit, the steady state coherence disappears and the efficiency approaches the heat engine limit given by Scovil and Schultz-Dubois in Phys. Rew. Lett. 2, 262 (1959).