Bacterial quantum tricks could help solar power

The ocean-dwelling Green Sulphur Bacteria should be interesting without outside help: it can, after all, live at depth of 2,000 meters and still harvest enough energy from light to survive and reproduce.

Now, researchers at Cambridge University have found that the little microbe has another interesting characteristic: its photosynthesis uses quantum physics to get the very most out of whatever light it finds.

Photosynthesis is already a quantum phenomenon, the University explains. The energy that a pigment like chlorophyll absorbs from photons is turned into an exciton and carried as a quantum wave to what they call the “reaction centre” of a pigment-protein complex (PPC), where the energy releases electrons necessary for the chemistry of photosynthesis.

Unlike a sun-drenched plant on the surface, the Green Sulphur Bacteria can’t afford to waste any of the energy it receives, so it has to prevent the excitons from dissipating. That’s what’s got the Cambridge scientists excited.

They’ve found a mechanism in the bacteria that captures some of the energy that might otherwise dissipate, by “reenergising it back to exciton level through molecular vibrations”. Its PPCs “ensure that every photon absorbed makes it to the structure’s reaction centre”.

The bacteria’s structure is able to preserve quantum coherence as the energy is transported, much more efficiently than happens in other systems. This, according to the University’s Dr Alex Chin, has important implications in solar cells, since their efficiency depends on their ability to capture energy from incoming photons.

“These biological systems can direct a quantum process, in this case energy transport, in astoundingly subtle and controlled ways – showing remarkable resistance to the aggressive, random background noise of biology and extreme environments,” he said.

“This new understanding of how to maintain coherence in excitons, and even regenerate it through molecular vibrations, provides a fascinating glimpse into the intricate design solutions – seemingly including quantum engineering – that nature has produced through evolution, and which could provide the inspiration for new types of room temperature quantum devices.”

The research is published in Nature, abstract here. ®