Quantum entanglement in photosynthesis?

Nanotechnology is, ultimately, a mechanization of the molecular processes of life. One of the most important of those processes is photosynthesis. If we really understood photosynthesis as deeply as we do, say, gear trains, and had the machinery to build whatever molecular machines we designed, we could build trees that produced gasoline from sunlight and the CO2 in the air.

(just for fun: a gasoline tree with an effective area of 100 m2 would produce about 3 gallons per hour of direct sunlight.)

Quantum entanglement is primarily a laboratory curiosity at the macroscopic scale (at the atomic scale nothing works without quantum mechanics, of course). The major uses that anyone is working on are quantum computing and cryptography. It’s generally thought that quantum effects vanish in systems as large and warm as living cells.

Now a paper from a group at Berkeley claims that quantum entanglement seems to be occurring in photosynthesis:

Light harvesting components of photosynthetic organisms are complex, coupled, many-body quantum systems, in which electronic coherence has recently been shown to survive for relatively long time scales despite the decohering effects of their environments. Within this context, we critically analyze entanglement in multi-chromophoric light harvesting complexes; we clarify the connection between coherence and entanglement in these systems, and establish methods for quantification of entanglement by presenting necessary and sufficient conditions for entanglement and by deriving a measure of global entanglement. These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to extract the initial state and temperature dependencies of entanglement in this complex. We show that while FMO in natural conditions largely contains bipartite entanglement between dimerized chromophores, a small amount of long-range and multipartite entanglement exists even at physiological temperatures. This constitutes the first rigorous quantification of entanglement in a biological system. Finally, we discuss the practical utilization of entanglement in densely packed molecular aggregates such as light harvesting complexes.

The observed entanglement only lasts for picosecond timescales, but that’s enough to affect a chemical reaction.

From later in the paper (LHC = Light Harvesting Complex):

… while entanglement in these systems is a by-product of this quantum coherence – since as discussed in this work, in the presence of coherence entanglement naturally exists for states in the single excitation subspace – it is however not clear whether it has a significant role in the functioning of light harvesting complexes. The non-local correlations of chromophoric electronic states that entanglement embodies are unlikely to impact excitation transport, the main function of LHCs. It is more plausible that entanglement exists merely as a consequence of the critical electronic coherence and the resulting excitation delocalization.
Even if it does not play a significant role in the light harvesting functioning of LHCs, the existence of entanglement in these systems has important practical implications due to the technological applications of entangled states. For example, the presence of entanglement in LHCs sets the stage for investigating the applicability of entanglement-enhanced precision measurement [41] in biological systems. …
In addition to precision metrology, densely packed molecular aggregates such as LHCs have potential for constructing naturally robust quantum devices. …

(H/T Technology Review)

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