Scale-estimation of quantum coherent energy transport in multiple-minima systems

TL;DR

This paper presents a quantum mechanical model demonstrating how resonance with vibrational modes can significantly enhance energy transfer efficiency in multi-minima systems, akin to biological light-harvesting complexes.

Contribution

It introduces a generic model for coherent energy transport in multi-minima systems coupled to a quantum bath, extending to complex systems like the FMO complex.

Findings

Resonance with vibrational modes can arbitrarily increase transfer efficiency.

Quantum coherence explains high efficiency in biological energy transfer.

Model applies to complex multi-site systems like FMO.

Abstract

A generic and intuitive model for coherent energy transport in multiple minima systems coupled to a quantum mechanical bath is shown. Using a simple spin-boson system, we illustrate how a generic donor-acceptor system can be brought into resonance using a narrow band of vibrational modes, such that the transfer efficiency of an electron-hole pair (exciton) is made arbitrarily high. Coherent transport phenomena in nature are of renewed interest since the discovery that a photon captured by the light-harvesting complex (LHC) in photosynthetic organisms can be conveyed to a chemical reaction centre with near-perfect efficiency. Classical explanations of the transfer use stochastic diffusion to model the hopping motion of a photo-excited exciton. This accounts inadequately for the speed and efficiency of the energy transfer measured in a series of recent landmark experiments. Taking a quantum mechanical perspective can help capture the salient features of the efficient part of that transfer. To show the versatility of the model, we extend it to a multiple minima system comprising seven-sites, reminiscent of the widely studied Fenna-Matthews-Olson (FMO) light-harvesting complex. We show that an idealised transport model for multiple minima coupled to a narrow-band phonon can transport energy with arbitrarily high efficiency.