  This paper investigates the dynamics of excitonic transport in photocomplex
LHCII, the primary component of the photosynthetic apparatus in green plants.
The dynamics exhibits a strong interplay between coherent processes mediated by
the excitonic Hamiltonian, and incoherent processes due to interactions with
the environment. The spreading of the exciton over a single monomer is well
described by a proper measure of delocalization that allows one to identify two
relevant time scales. An exciton initially localized in one chromophore first
spreads coherently to neighboring chromophores. During this initial coherent
spreading, quantum effects such as entanglement play a role. As the effects of
a decohering environment come into play, coherence and decoherence interact to
give rise to efficient and robust excitonic transport, reaching a maximum
efficiency at the levels of decoherence found in physiological conditions. We
analyze the efficiency for different possible topologies (monomer, dimer,
trimer, tetramer) and show how the trimer has a particular role both in the
antenna and the wire configuration.
