Environment-Assisted Quantum Walks in Photosynthetic Energy Transfer

TL;DR

This paper develops a theoretical framework to study quantum interference effects in photosynthetic energy transfer, showing that environmental interactions can significantly enhance transfer efficiency.

Contribution

It generalizes quantum walks to non-unitary, temperature-dependent dynamics, revealing how environment-assisted quantum effects improve energy transfer in photosynthesis.

Findings

Quantum coherence enhances energy transfer efficiency.

Environmental fluctuations increase efficiency from 70% to 99%.

Theoretical model matches experimental observations.

Abstract

Energy transfer within photosynthetic systems can display quantum effects such as delocalized excitonic transport. Recently, direct evidence of long-lived coherence has been experimentally demonstrated for the dynamics of the Fenna-Matthews-Olson (FMO) protein complex [Engel et al., Nature 446, 782 (2007)]. However, the relevance of quantum dynamical processes to the exciton transfer efficiency is to a large extent unknown. Here, we develop a theoretical framework for studying the role of quantum interference effects in energy transfer dynamics of molecular arrays interacting with a thermal bath within the Lindblad formalism. To this end, we generalize continuous-time quantum walks to non-unitary and temperature-dependent dynamics in Liouville space derived from a microscopic Hamiltonian. Different physical effects of coherence and decoherence processes are explored via a universal measure for the energy transfer efficiency and its susceptibility. In particular, we demonstrate that for the FMO complex an effective interplay between free Hamiltonian and thermal fluctuations in the environment leads to a substantial increase in energy transfer efficiency from about 70% to 99%.