Physicists have found the strongest evidence yet of quantum effects fueling photosynthesis.
Multiple experiments in recent years have suggested as much, but it's been hard to be sure. Quantum effects were clearly present in the light-harvesting antenna proteins of plant cells, but their precise role in processing incoming photons remained unclear.
In an experiment published Dec. 6 in Proceedings of the National Academy of Sciences, a connection between coherence—far-flung molecules interacting as one, separated by space but not time—and energy flow is established.
"There was a smoking gun before," said study co-author Greg Engel of the University of Chicago. "Here we can watch the relationship between coherence and energy transfer. This is the first paper showing that coherence affects the probability of transport. It really does change the chemical dynamics."
The new findings are the latest in a series that have, piece by piece, promised to expand scientific understanding of photosynthesis, one of life's fundamental processes. Until a few years ago, it seemed a straightforward piece of chemistry.
Then came observations of coherence in antenna-protein chlorophylls from green sulfur bacteria. They lasted far longer than anyone expected, long enough to hint at a functional role. Those observations were, however, made at unrealistically ultracold temperatures; then they were made at room temperatures, and in antenna proteins found in plants everywhere.
Confronted with this unexpected coherence, researchers hypothesized a role in enabling ultra-efficient energy transfer. Energy from incoming photons could simultaneously explore every possible chlorophyll route from a protein's surface to the reaction center at its core, then settle on the shortest path.
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Generalizing to the 'quantum mind' program seems hazardous, at best, as we would need to establish that our brains are at least as complex as vegetable matter, for example.
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