  Photosynthesis is a highly efficient process, nearly 100 percent of the red
photons falling on the surface of leaves reach the reaction center and get
transformed into energy. Most theoretical studies on photosynthetic complexes
focus mainly on the Fenna-Matthews-Olson complex obtained from green-sulfur
bacteria. Quantum coherence was speculated to play a significant role in this
very efficient transport process. However, recent reports indicate quantum
coherence via exciton transport may not be as relevant as coherence originating
via vibronic processes to Photosynthesis. Regardless of the origin, there has
been a debate on whether quantum coherence results in any speedup of the
exciton transport process. To address this we model exciton transport in FMO
using a quantum stochastic walk (QSW) with only incoherence, pure dephasing,
and with both dephasing and incoherence. We find that the QSW model with pure
dephasing leads to a substantial speedup in exciton transport as compared to a
QSW model which includes both dephasing and incoherence and one which includes
only incoherence, both of which experience slowdowns.
