We provide physically intuitive mechanisms for the effect of noise
on excitation energy transfer (EET) in networks. Using these mechanisms of
dephasing-assisted transport (DAT) in a hybrid basis of both excitons and
sites, we develop a detailed picture of how noise enables energy transfer with
efficiencies well above 90% across the Fenna–Matthew–Olson (FMO) complex,
a type of light-harvesting molecule. We demonstrate explicitly how noise alters
the pathways of energy transfer across the complex, suppressing ineffective
pathways and facilitating direct ones to the reaction centre. We explain that
the fundamental mechanisms underpinning DAT are expected to be robust with
respect to the considered noise model but show that the specific details of
the exciton–phonon coupling, which remain largely unknown in these type
of complexes, and in particular the impact of non-Markovian effects, result
in variations of dynamical features that should be amenable to experimental
verification with current or planned technology. A detailed understanding of DAT
in natural compounds could open up a new paradigm of ‘noise-engineering’ by
which EET can be optimized in artificial light-harvesting structures.