量子效应有助细胞捕捉阳光

Sophisticated recent experiments with ultrashort laser pulses support the idea that intuition-defying quantum interactions between molecules¹ help plants, algae²（藻类）, and some bacteria efficiently³ gather light to fuel their growth. But key details of nature's vital light-harvesting mechanisms⁴ remain obscure, and the exact role that quantum physics may play in understanding them is more subtle than was once thought, according to an Overview⁵ Article in the January issue of BioScience. The article, by Jessica M. Anna and Gregory D. Scholes of the University of Toronto and Rienk van Grondelle of Vrije Universiteit in Amsterdam, describes experiments that employ a technique called 2-D electronic spectroscopy. Researchers flash laser pulses at the light-harvesting protein molecules of bacteria and algae, timed to within a billionth of a billionth of a second, then observe how the energized⁶ molecules re-emit light of different colors in the ensuing（接着发生的） instants. This allows investigators⁷ to deduce how energy is stored by and moves among the molecules. But the results would be impossible to explain if captured light energy were conveyed by discrete⁸（离散的） entities⁹ moving randomly¹⁰ between molecules. Rather, the insights of quantum mechanics are needed.

 

Quantum mechanics envisages¹¹ particles as being smeared¹² over regions of space, rather than being pointlike, and as interfering¹³ with each other like waves. The smearing¹⁴ is undetectable in everyday life, but the experimental results indicate that, within arrays of light-harvesting molecules that serve as light "antennas¹⁵" inside cells, such "coherence¹⁶" eases ultrafast energy transfers that help organisms use solar energy. It thus allows life to pervade¹⁷ the planet, using the process known as photosynthesis¹⁸（光合作用） to extract carbon dioxide from the air.

 

Yet Anna and her colleagues point out that the molecular¹⁹ details of the light-gathering²⁰ apparatus²¹ have evolved very differently in different species, so there is nothing simple about how organisms exploit quantum coherence. Indeed, coherence, contrary to what some researchers have speculated, does not seem to dominate light gathering by providing an express route for conveying energy from where it is first captured to the chemical reaction center where it is used. Instead, Anna and her colleagues write, researchers should "inquire how coherence on short length and time scales might seed some kind of property or function" in light-gathering systems. Such understanding might help scientists devise environmentally friendly solar technologies that could regulate their rate of energy input²² and redistribute and repair their components²³ when the need arises, as living cells do.

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