A dash of sunlight, a sprinkle of light-harvesting proteins and a healthy dollop of carbon dioxide is about all it takes to whip up a batch of tasty plant food — but you might want some quantum physics to stir the pot. Scientists have caught photosynthetic lake-dwelling algae performing long-lasting quantum tricks at room temperature. The results, published February 4 in Nature, suggest that quantum mechanics may be at the heart of sunlight-to-energy conversion in living organisms.
“This is quantum mechanics in a biological system,” says study coauthor Gregory Scholes, a physical chemist at the University of Toronto.
Photosynthesis relies on special proteins that absorb incoming photons, or particles of light. These photons excite electrons in the protein, touching off a series of electron transfers that ultimately ferry the energy-laden electrons to centralized collection stations (called photosystems) where the conversion of energy to carbohydrates begins.
Under normal, everyday rules, electrons would make their way to their destinations with quick random hops. But recent studies of photosynthetic bacteria and plants suggest that the electrons might act more like correlated waves instead of hopping particles, a behavior predicted by quantum mechanics (SN: 5/9/09, p. 26). These studies have mainly seen such quantum effects at very low temperatures, where the system is held very still. Scholes and colleagues devised an experiment to see whether these quantum-mechanical wavelike properties were also present at normal temperatures.
The researchers purified the light-catching proteins from two types of photosynthetic algae called cryptophytes. At room temperature, the team shone a laser onto the proteins to excite them and used a second laser pulse to see where the excited electrons traveled. Patterns of long-lasting electron waves — a property called quantum coherence — indicated that quantum weirdness was at work.