  We show that quantum coherence of biomolecular excitons is maintained over
exceedingly long times due to the constructive role of their non-Markovian
protein-solvent environment. Using a numerically exact approach, we demonstrate
that a slow quantum bath helps to sustain quantum entanglement of two pairs of
Forster coupled excitons, in contrast to a Markovian environment. We consider
the crossover from a fast to a slow bath and from weak to strong dissipation
and show that a slow bath can generate robust entanglement. This persists to
surprisingly high temperatures, even higher than the excitonic gap and is
absent for a Markovian bath.
