  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.
