A prominent goal of quantum information and computing is to be able to exploit quantum entanglement in qualitatively new devices, such as massively parallel computers. Has biological evolution already harnessed entanglement for its own purposes? Recent studies have indeed suggested that electronic excitation transfer (EET) in photosynthesis benefits from quantum entanglement. Now, a paper appearing in Physical Review E is likely to stimulate further investigation and controversy on this question. Based on calculations, John Briggs and Alexander Eisfeld, of the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, assert that under the conditions prevailing in photosynthesis (in particular, in the so-called Fenna-Matthews-Olson complex that lies at the heart of the process), energy transfer in a classical system is just as efficient as in its quantum counterpart.
To model the photosynthesis that occurs in plants, Briggs and Eisfeld study a collection of monomers, each possessing a single electronic state and coupled to its neighboring units by a dipolar interaction. The authors find that for dipolar interactions similar to those found in real molecular aggregates, the coherences in quantum transport (from the Schrödinger equation) are identical to those occurring in classical transport according to Newton’s equation. Although their analysis neglects the influence of the environment, the authors report that calculations including dephasing processes in the quantum and classical equations lead to the same conclusion. – Ron Dickman