Skip to ContentSkip to Navigation
Part of University of Groningen
Science LinXScience Linx News

Quantum effects observed in photosynthesis

22 May 2018

Molecules that are involved in photosynthesis exhibit the same quantum effects as non-living matter, concludes an international team of scientists including University of Groningen theoretical physicist Thomas la Cour Jansen. Quantum mechanical behavior was found at a temperature of 77 Kelvin, much too low to play a biological role. The interpretation of these quantum effects in photosynthetic systems may help in the development of nature-inspired light-harvesting devices and the present research may help identify quantum effect is other systems. The results were published in Nature Chemistry on 21 May.

For several years now, there has been a debate about quantum effects in biological systems. The basic idea is that electrons in can be in two states at once, until they are observed. This may be compared to the thought experiment known as ‘Schrödinger's Cat’. The cat is locked in a box with a vial of a toxic substance. If the cap of the vial is locked with a quantum system, it may simultaneously be open or closed, so the cat is in a mixture of the states "dead" and "alive", until we open the box and observe the system. This is precisely the apparent behavior of electrons.

Thomas la Cour Jansen | Photo ZIAM/University of Groningen
Thomas la Cour Jansen | Photo ZIAM/University of Groningen

Vibrations

In earlier research, scientists had already found signals suggesting that light-harvesting molecules in bacteria may be excited into two states simultaneously. In itself this proved the involvement of quantum mechanical effects, however in those experiments, that excited state supposedly lasted more than 1 picosecond (0.000 000 000 001 second). This is much longer than one would expect on the basis of quantum mechanical theory.

Jansen and his colleagues show in their publication that this earlier observation is wrong. "We have shown that the quantum effects they reported were simply regular vibrations of the molecules." Therefore, the team continued the search. "We wondered if we might be able to observe that Schrödinger cat situation."

Superposition

They used different polarizations of light to perform measurements in light-harvesting green sulfur bacteria. The bacteria have a photosynthetic complex, made up of seven light sensitive molecules. A photon will excite two of those molecules, but the energy is superimposed on both. So just like the cat is dead or alive, one or the other molecule is excited by the photon.
The figure shows the photosynthetic complex of light-harvesting green sulfur bacteria the green and yellow circles highlight the two molecules simultaneously excited. | Illustration Thomas la Cour Jansen/University of Groningen
The figure shows the photosynthetic complex of light-harvesting green sulfur bacteria the green and yellow circles highlight the two molecules simultaneously excited. | Illustration Thomas la Cour Jansen/University of Groningen

"In the case of such a superposition, spectroscopy should show a specific oscillating signal", explains Jansen. "And that is indeed what we saw. Furthermore, we found quantum effects that lasted precisely as long as one would expect based on theory and proved that these belong to energy superimposed on two molecules simultaneously." Jansen concludes that biological systems exhibit the same quantum effects as non-biological systems. But at the normal operating temperatures for biological systems, like bacteria, the effects are too weak to determine the efficiency in the photosynthetic systems, which others have suggested.

The observation techniques developed for this research project may be applied to different systems, both biological and non-biological. Jansen is happy with the results. "This is an interesting observation for anyone who is interested in the fascinating world of quantum mechanics. Moreover, the results may play a role in the development of new systems, such as the storage of solar energy or the development of quantum computers."

Reference: Erling Thyrhaug, Roel Tempelaar, Marcelo J. P. Alcocer, Karel ?ídek, David Bína, Jasper Knoester, Thomas L. C. Jansen and Donatas Zigmantas: Identification and characterization of diverse coherences in the Fenna-Matthews-Olson complex. Nature Chemistry 21 May 2018.

Text: Christine Dirkse

Last modified:31 May 2018 2.22 p.m.
printView this page in: Nederlands

More news

  • 23 August 2019

    Opening of the Academic Year 2019-2020

    Programme


    4 to 5.30 p.m.

    • Opening speech by Prof.dr. Cisca Wijmenga, Rector Magnificus
    • Musical interlude
    • Award Ceremony Ubbo Emmius Penning (Scientific)
    • Award Ceremony Alumnus of the Year 2018 Christiaan Triebert, MA
    • Musical interlude
    • Academic speech...
  • 13 August 2019

    Eat, sleep, recycle

    The 51st edition of KEI week is devoted to the theme of sustainability. On Monday 12 August, around 6,000 KEI participants and KEI leaders were handed cloth bags instead of plastic ones and a KEI wristband with a chip enabling digital payments. A vegetarian...

  • 12 August 2019

    Cold winters not caused by Arctic climate change

    Recent studies into the relationship between decreases in sea ice in the Arctic and ice-cold winters in the mid-latitudes, like the Polar Vortex cold waves in North America, seem to suggest that such a connection does indeed exist. However, the mechanisms...