  An important challenge in quantum science is to fully understand the
efficiency of energy flow in networks. Here we present a simple and intuitive
explanation for the intriguing observation that optimally efficient networks
are not purely quantum, but are assisted by some interaction with a `noisy'
classical environment. By considering the system's dynamics in both the
site-basis and the momentum-basis, we show that the effect of classical noise
is to sustain a broad momentum distribution, countering the depletion of high
mobility terms which occurs as energy exits from the network. This picture
predicts that the optimal level of classical noise is reciprocally related to
the linear dimension of the lattice; our numerical simulations verify this
prediction to high accuracy for regular 1D and 2D networks over a range of
sizes up to thousands of sites. This insight leads to the discovery that
dramatic further improvements in performance occur when a driving field targets
noise at the low mobility components.
