  Exciton transfer along a polymer is essential for many biological processes,
for instance light harvesting in photosynthetic biosystems. Here we apply a new
witness of non-classicality to this phenomenon, to conclude that, if an exciton
can mediate the coherent quantum evolution of a photon, then the exciton is
non-classical. We then propose a general qubit model for the quantum transfer
of an exciton along a polymer chain, also discussing the effects of
environmental decoherence. The generality of our results makes them ideal
candidates to design new tests of quantum features in complex bio-molecules.
