New research from the University of New South Wales has pinpointed a specific gene in algae that is capable of switching quantum coherence on and off. Some experimental findings suggest that algae and other organisms can utilize quantum coherence to make the harvesting of light for photosynthesis more efficient. But to date this and other phenomena in the field of quantum biology remain quite mysterious. Experts speculate that a better understanding of the principles behind quantum coherence and other quantum events in biology may one day serve to help in the optimization of technologies such as solar cells and quantum-based electronics.
The study of quantum mechanics is traditionally most closely associated with the fields of mathematics and physics. But because quantum mechanics deals specifically with the behavior of matter, by extension the world it describes also can be related to chemistry. Beyond even that, matters of chemistry are essential to understanding biology. While many find it near impossible imagine the abstract and probability-based world of quantum mechanics intersecting with the world of familiar living systems, starting in the early 2010s scientists began exploring this notion in what has since been named “quantum biology.”
One of the more intriguing questions quantum biologists are exploring is the phenomenon of quantum coherence during photosynthesis. Plants and other photosynthesizing organisms are equipped with a complex set of machinery that helps them capture light and turn it into chemical energy. Some of the more important features in this system are the “antennae” that capture incoming photons (particles of light). Photons that hit these antennae bounce in all directions, therefore one might expect that capturing this energy and efficiently channeling it would be difficult. But instead, algae and other organisms are capable of smoothly channeling this energy into the photoreaction systems with up to 99 percent efficiency. To explain this strange phenomenon, researchers have proposed that forces more familiar to the world of quantum mechanics are at play.
Plant physiologists understand that light that hits a plant is absorbed and transferred to reaction centers along chains of pigment-protein complexes (PPCs). As energy moves down the molecular links in a PPC chain, they raise the energy of those individual molecules and create “excitons.” At this point, proponents of the idea of quantum coherence suggest that these excitons are capable of existing simultaneously in different quantum superpositions with varying degrees of probability. The ability to exist in multiple states at the same time would allow excitons to “explore” different pathways in which energy is transferred. Ultimately if plants construct their PPCs to favor the smooth transfer of energy to a reaction center, this “easier” route will be statistically more favorable and lead to the smooth and efficient channeling of solar energy.
Scientists have found both direct and indirect evidence of quantum coherence playing a role in optimizing energy transfer during photosynthesis. In 2013 researchers from the Institute of Photonic Sciences and the University of Glasgow published a report in which they announced that they had been able to photograph the transfer of energy down PPCs. The images that they captured using ultra-fast photospectroscopy were indicative of quantum coherence at work.
In one of the latest studies on the subject, senior author Professor Paul Curmi and his team searched for a genetic basis of quantum coherence. Curmi’s team examined cryptophytes—a particularly hearty variety of algae that have adapted to live in specific niches where little light penetrates. They can be found under thick layers of ice or at the bottom of pools of water. Professor Curmi and his team identified a particular sub population of cryptophytes that did not display quantum coherence. Genetic analysis revealed that this was due to a single insertion mutation at a specific genetic locus. Using x-ray crystallography, it became apparent that this mutation caused a mis-shaping of the light harvesting proteins that the cryptophytes use for photosynthesis.
Though it is still in its infancy, the field of quantum biology has the potential to help develop more efficient technologies. In particular photocell technology, which at its best currently runs at only about 20 percent efficiency, could stand to be greatly improved by mimicking how plants use quantum coherence to achieve such stellar efficiency levels. In addition, quantum biology may yet reveal some extraordinary insights into the forces that shaped the evolutionary history of life on Earth.
By Sarah Takushi