  The influence of fast vibrations on energy transfer and conversion in natural
molecular aggregates is an issue of central interest. This article shows the
important role of high-energy quantized vibrations and their non-equilibrium
dynamics for energy transfer in photosynthetic systems with highly localized
excitonic states. We consider the cryptophyte antennae protein phycoerythrin
545 and show that coupling to quantized vibrations which are quasi-resonant
with excitonic transitions is fundamental for biological function as it
generates non-cascaded transport with rapid and wider spatial distribution of
excitation energy. Our work also indicates that the non-equilibrium dynamics of
such vibrations can manifest itself in ultrafast beating of both excitonic
populations and coherences at room temperature, with time scales in agreement
with those reported in experiments. Moreover, we show that mechanisms
supporting coherent excitonic dynamics assist coupling to selected modes that
channel energy to preferential sites in the complex. We therefore argue that,
in the presence of strong coupling between electronic excitations and quantized
vibrations, a concrete and important advantage of quantum coherent dynamics is
precisely to tune resonances that promote fast and effective energy
distribution.
