Explaining the Efficiency of Photosynthesis: Quantum Uncertainty or Classical Vibrations?

Photosynthetic organisms
are known to use a mechanism of vibrationally
assisted exciton energy transfer to efficiently harvest energy from
light. The importance of quantum effects in this mechanism is a long-standing
topic of debate, which has traditionally focused on the role of excitonic
coherences. Here, we address another recent claim: that the efficient
energy transfer in the Fenna–Matthews–Olson complex
relies on nuclear quantum uncertainty and would not function if the
vibrations were classical. We present a counter-example to this claim,
showing by trajectory-based simulations that a description in terms
of quantum electrons and classical nuclei is indeed sufficient to
describe the funneling of energy to the reaction center. We analyze
and compare these findings to previous classical-nuclear approximations
that predicted the absence of an energy funnel and conclude that the
key difference and the reason for the discrepancy is the ability of
the trajectories to properly account for Newton’s third law.