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Leafy Green Coherence: Quantum Physics Fuels Photosynthesis
Wired
July 7, 2010
Not so long ago, quantum physics at room temperature was found mostly in classroom discussions or over science-geek cocktails. But the mind-bending mechanics seems to be present in many everyday phenomena - including photosynthesis, the driving force behind life's harvest of solar energy.
A process called coherence allows photon energy to find the shortest path through a leaf's surface by taking all possible paths simultaneously, then "picking" the best one. The resulting energy transfer is almost perfectly efficient.
"Coherence is well-known in energy transfer in nonbiological systems," said Elad Harel, a University of Chicago physicist. "The question was whether biological systems take advantage of this as well."
In a paper published July 6 in the Proceedings of the National Academy of Sciences, physicists led by the University of Chicago's Greg Engels describe coherence in the FMO protein complex. A wildly complicated tangle of molecules, the FMO complex directs energy from photon-sensitive "antenna" proteins on a photosynthetic bacterium's surface to internal, charge-converting proteins.
To measure coherence, the researchers charged antennae with brief laser pulses, then measured fluctuations in another laser beam that shone through the FMO complex. Fluctuations corresponded to energy passing from the antennae through the complex's molecules.
Distant molecules quivered in tandem - a phenomenon possible only through coherence, in which energy exists in multiple, linked states simultaneously. Once energy has explored the possible routes through the FMO complex and found the most efficient one, it collapses back into a single state.
The findings dovetail with research by University of Toronto biophysicist Greg Scholes, who found coherence in the photosynthesis of a common marine algae. Scholes showed indisputably that coherence - previously observed only in ultracold temperatures in nonbiological systems - could happen in biology, at room temperature. Because the FMO complex is used as a model system for plant photosynthesis, Engels' findings suggest that coherence is everywhere in the leafy green world.
Researchers hope these findings will guide the design of solar panels that are as efficient as nature's, said Harel. In the meantime, scientists will continue looking for more evidence of quantum biology, which has been also been posited in the structure of DNA and operations of the mind.
"I'd be surprised" if quantum effects are not ubiquitous in biology, said Harel. "To have a tool at your disposal, and not use it, is not a law of biology."
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