Everywhere in a Flash: The Quantum Physics of Photosynthesis

By | February 5, 2010

leafveinsBy hitting single molecules with quadrillionth-of-a-second laser pulses, scientists have revealed the quantum physics underlying photosynthesis, the process used by plants and bacteria to capture light’s energy at efficiencies unapproached by human engineers.

The quantum wizardry appears to occur in each of a photosynthetic cell’s millions of antenna proteins. These route energy from electrons spinning in photon-sensitive molecules to nearby reaction-center proteins, which convert it to cell-driving charges.

Almost no energy is lost in between. That’s because it exists in multiple places at once, and always finds the shortest path.

“The analogy I like is if you have three ways of driving home through rush hour traffic. On any given day, you take only one. You don’t know if the other routes would be quicker or slower. But in quantum mechanics, you can take all three of these routes simultaneously. You don’t specify where you are until you arrive, so you always choose the quickest route,” said Greg Scholes, a University of Toronto biophysicist.

Scholes’ findings, published Wednesday in Nature, are the strongest evidence yet for coherence — the technical name for multiple-state existence — in photosynthesis.

Two years ago, researchers led by then-University of California at Berkeley chemist Greg Engel found coherence in the antenna proteins of green sulfur bacteria. But their observations were made at temperatures below minus 300 degrees Fahrenheit, useful for slowing ultrafast quantum activities but leaving open the question of whether coherence operates in everyday conditions.

The Nature findings, made at room temperature in common marine algae, show that it does. Moreover, similar results from an experiment on another, simpler light-harvesting structure, announced by Engel’s group last Thursday on the pre-publication online arXiv, suggest that photosynthetic coherence is routine.

The findings are wondrous in themselves, adding a new dimension to something taught — incompletely, it now seems — to every high school biology student. They also have important implications for designers of solar cells and computers, who could benefit from quantum physics conducted in nonfrigid conditions.

“There’s every reason to believe this is a general phenomenon,” said Engel, now at the University of Chicago. He called Scholes’ finding “an extraordinary result” that “shows us a new way to use quantum effects at high temperatures.”

Scholes’ team experimented on an antenna protein called PC645, already imaged at the atomic scale in earlier studies. That precise characterization allowed them to target molecules with laser pulses lasting for one-quadrillionth of a second, or just long enough to set single electrons spinning.

via Everywhere in a Flash: The Quantum Physics of Photosynthesis | Wired Science | Wired.com.

If quantum effects make photosynthesis possible, I think we will find eventually also find that consciousness is enabled by quantum processing in the brain.

The quantum mind hypothesis proposes that classical mechanics cannot fully explain consciousness, and suggests that quantum mechanical phenomena such as quantum entanglement and superposition may play an important part in the brain’s function and could form the basis of an explanation of consciousness. …

The main argument against the quantum mind proposition is that quantum states would decohere too quickly to be relevant to neural processing. Possibly the scientist most often quoted in relation to this criticism is Max Tegmark. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function.

Proponents of the various quantum consciousness theories have sought to defend them against Tegmark’s criticism. In respect of QBD, Vitiello has argued that Tegmark’s work applies to theories based on quantum mechanics but not to those such as QBD that are based on quantum field theory. In respect of Penrose and Hameroff’s Orch OR theory, Hameroff along with Hagan and Tuszynski replied to Tegmark.[34] They claimed that Tegmark based his calculations on a model that was different from Orch OR. It is argued that in the Orch OR model, the microtubules are shielded from decoherence by ordered water. Energy pumping as a result of thermal disequilibrium, Debye layer screening and quantum error correction, deriving from the geometry of the microtubule lattice are also proposed as possible sources of shielding. Similarly, in his extension of Bohm’s ideas, Bernroider has claimed that the binding pockets in the ion selection filters could protect against decoherence[4].

So far, however, there has been no experimental confirmation of the ability of the features mentioned above to protect against decoherence, although a paper in Nature by Gregory Engel (April, 2007) on quantum coherent energy transfer in photosynthetic protein relates to quantum coherence and ‘quantum computing’ in living matter. …. – wiki

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