Quantum behaviour has been discovered in algae
Image: CSIRO

Researchers have discovered that algae in low-light conditions are able to switch a quantum behaviour off and on during photosynthesis.

The team led by scientists from the University of New South Wales in Australia suspect this could help the algae harvest energy from the Sun more efficiently.

The phenomenon is quantum coherence. A system that is coherent - with all quantum waves in step with each other - can exist in many different states at once, an effect known as superposition.

Usually scientists only see this behaviour occurring the lab, but the scientists were surprised to find that the transfer of energy between molecules in the light harvesting systems of two different algae was coherent.

The work was done on cryptophytes, single-celled organisms that live at the bottom of pools of water or under thick ice, in very low levels or light.

Learning more about why these algae switch quantum coherence on and off could lead to technological advances, such as better organic solar cells and quantum-based electronic devices. The research is published in the journal Proceedings of the National Academy of Sciences.

“Most cryptophytes have a light-harvesting system where quantum coherence is present. But we have found a class of cryptophytes where it is switched off because of a genetic mutation that alters the shape of a light-harvesting protein,” senior author, Professor Paul Curmi, of the UNSW School of Physics, explained in a press release.

“This is a very exciting find. It means we will be able to uncover the role of quantum coherence in photosynthesis by comparing organisms with the two different types of proteins.”

Quantum coherence has also been found in green sulphur bacteria that also survive in very low light levels. “The assumption is that this could increase the efficiency of photosynthesis, allowing the algae and bacteria to exist on almost no light,” said Professor Curmi.

“Once a light-harvesting protein has captured sunlight, it needs to get that trapped energy to the reaction centre in the cell as quickly as possible, where the energy is converted into chemical energy for the organism. It was assumed the energy gets to the reaction centre in a random fashion, like a drunk staggering home. But quantum coherence would allow the energy to test every possible pathway simultaneously before travelling via the quickest route.”

The researchers used X-ray crystallography to look at the structure of these light-harvesting systems from three different cryptophyte species. They found that the two species that could turn the coherence off had a genetic mutation that led to the insertion of an extra amino acid in the protein complex.

The next step is to work out whether these species live in different environmental niches, to better understand whether the quantum coherence is helping them survive.

The research is part of an emerging field called quantum biology, which is studying quantum phenomena outside the lab. It's becoming increasingly clear that these behaviours are present in nature - in fact they might even account for how birds navigate using the Earth’s magnetic field.