QUANTUM SECRET: Marine algae, like the Chroomonas pictured here, employ quantum coherence to boost the efficiency of photosynthesis.
Image: Courtesy of Provasoli-Guillard National Center for Culture of Marine Phytoplankton
In less than one billionth of a second, plants from algae to redwoods transform 95 percent of the sunlight that falls on them—1017 joules per second bathe the planet—into energy stored chemically as carbohydrates. The quantum key to doing that lies in a phenomenon known to physicists as quantum coherence, according to new research published in Nature on February 4. (Scientific American is part of Nature Publishing Group.)
Quantum coherence describes how more than one molecule interacts with the same energy from one incoming photon at the same time. In essence, rather than the energy from a particular photon choosing one route to pass through the photosynthetic system, it travels through multiple channels simultaneously, allowing it to pick the quickest route. "The energy of the absorbed light is finding more than one pathway to move along at any one time," explains physical chemist Greg Scholes of the University of Toronto, leader of the research group that highlighted the effect. "We can't pinpoint the energy of that light. It's shared in a very special way."
Scholes and his colleagues isolated the "antenna" (a protein chain that propagates the incoming energy) of photosynthetic organisms known as cryptophytes, specifically marine algae Rhodomonas CS24 and Chroomonas CCMP270. Cryptophytes are special because they do not all employ the same protein to harvest the energy in sunlight, like the chlorophyll ubiquitous in green plants. "These guys customize their antenna protein," Scholes says, noting that the algae also have flagella that permit them to move around. "They're quite different colors."
The algae's different antenna colors allowed the chemists to pulse the specific proteins with femtosecond (one quadrillionth of a second) bursts of laser light. Based on atomic scale maps provided by previous X-ray crystallography, the researchers tracked the energy as it entered the photosynthetic system and progressed through it to so-called reaction centers, where the energy storage occurs. The pulses revealed that within single protein molecules the energy traveled down multiple pathways simultaneously. Thus, the protein antennae's efficiency relies on quantum coherence, such that molecules within a protein separated by vast distances (at the atomic scale) acted in a similar fashion at the same time for a relatively long period of time—more than 400 femtoseconds.
Whereas previous research had shown that purple bacteria used quantum methods to efficiently harness light—and prior experiments had shown similar quantum effects in green sulfur bacterium that had been cooled to 77 kelvins (–196 degrees Celsius)—this experiment was the first conducted at room temperature, 294 K, to replicate such effects. Basically, according to this research, an incoming photon created a series of ripples, like a stone thrown into a pond, that interfere with each other to allow the energy wave to explore all potential pathways through a given protein molecule at the same time, allowing no energy to be lost to any wrong paths. It is as if you could drive to work via three different routes at the same time, losing no time or energy to traffic delays on any of the given routes, Scholes says. That allows the photon to travel to the reaction center almost instantaneously.
"In the systems we studied, even at room temperature, you can have these quantum effects and they're rather significant," Scholes notes, adding that means the effects are "biologically relevant" (used by the cryptophytes in their daily existence.). "The short laser pulse is used to expose the phenomenon, not to create it."
Chemist Graham Fleming at the University of California, Berkeley, has shown that such effects are visible in chlorophyll systems at low temperature. And biophysicist Gregory Engel of the University of Chicago, who was not involved in this research, argues that such effects are therefore likely to be used in all photosynthetic systems, allowing plants to efficiently transfer energy over long atomic distances. "That this effect appears in cryptophytes speaks to the generality of the process," Engel says. "This work will open the floodgates to new techniques to move and concentrate energy efficiently. It is extremely important for semiconductor devices [and] solar light harvesting."
In fact, such insights might help inform how to efficiently transfer energy over long atomic distances quickly in human-made systems to harvest sunlight—benefiting from nature's 2.7-billion-year head start in optimizing such systems. "Can it help you make a huge jump through space? It does precisely that," Scholes says. "It would be really nice to learn some tricks or what you need to think about if you want to design something that would move energy a long distance quickly."
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27 Comments
Add Comment"In less than one billionth of a second, plants from algae to redwoods transform 95 percent of the sunlight that falls on them1017 joules per second bathe the planetinto energy stored chemically as carbohydrates." - Article
Reply | Report Abuse | Link to thisThis is incorrect. Photosynthesis has an efficiency of only around 7%
the 95% transformation rate of the photons doesn't have anything to do with the efficiency of photosynthesis as a process. It's similar to your car being able to convert nearly 100% of it's gasoline fuel into energy but the car only being 50% (example number) efficient as a transportation process with much of the transformed energy being loss as heat, rolling friction, and wind resistance.
Reply | Report Abuse | Link to thisYou have a good point vendicar9. The writer should have made it clear that 95% efficiency is for light that is actually captured -- not for all the light that falls on plants or algae. Much of the total light energy falling on a plant is not captured. For example, light that does not have a wavelength within the 400-700nm range is can't be used at all.
Reply | Report Abuse | Link to thisIt is nice, but most likely has nothing to do with quantum coherence. Proteins can resonate this fast with "instantaneous" conformational changes that spread whitin a single protein or even to surrounding proteins.
Reply | Report Abuse | Link to thisthe 95% transformation rate of the photons doesn't have anything to do with the efficiency of photosynthesis as a process." - alanrp
Reply | Report Abuse | Link to thisI fully realize that the article's wording confused photosynthetic efficiency with photocurrent conversion efficiency.
Hence my correction.
Great comments. These answered my questions EXACTLY. Occasionally, useful stuff breaks through the noise of the Internet. Thank you both!
Reply | Report Abuse | Link to thisReally? Where's your data? We have physicists performing proper experiments and research with a repeatable experiment using all kinds of nifty equipment, complex math and big words...and then we have an anonymous schlub on the Internet. Hmmm...I wonder which one I should pay attention to?
Reply | Report Abuse | Link to thisHere is an explanation of photosynthetic efficiency from Wikipedia:
Reply | Report Abuse | Link to thisThe value of the photosynthetic efficiency is dependent on how light energy is defined. On a molecular level, the theoretical limit in efficiency is 25 percent[1] for photosynthetically active radiation (wavelengths from 400 to 700 nanometer). For actual sunlight, where only 45 percent of the light is photosynthetically active, the theoretical maximum efficiency of solar energy conversion is approximately 11 percent. In actuality, however, plants do not absorb all incoming sunlight (due to reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels) and do not convert all harvested energy into biomass, which results in an overall photosynthetic efficiency of 3 to 6 percent of total solar radiation.[1]
This is a much better synopsis than what I've seen elsewhere. All of chemistry is governed by the rules of quantum mechanics. It is nice that this article points out what is unique here.
Reply | Report Abuse | Link to thisWhat percentage of available energy is converted to heat in say a 10% albeido surface? Is it 90%, or is some of the energy not converted to heat, beyond that 10% reflection? I'd like to know so I can compare photosynthesis to thermal systems for solar energy collection concepts. Thanks.
Reply | Report Abuse | Link to thisYour AWARENESS (personel black hole) need very little energy.My father had said "don't be afraid to go in the junkle find the food there". NIRVANA.....
Reply | Report Abuse | Link to thisSorry to do this to an intelligent conversation, but I specialize in the noise of the Internet and this topic reminded me of a key assumption of homeopathy, which is that substances in a solution even when diluted far past any chance of still having a molecule in any given moleculre, are still, in some sense, "there."
Reply | Report Abuse | Link to thisThis has always suggested to me that the quantum superposition has some lingering tangible essence. Say you have diluted water to a point that there is no chance at all of any salt being left in it, still even a chance of something tunneling back in becomes a kind of ghost trace of the original pollutant.
Can anybody understand what I am getting at?
Maybe these multiple pathways could be explained if light was treated as a wave not a particle;-)
Reply | Report Abuse | Link to thisMike Cook...I like your examples...I think it means that below a certain level its all probablities...let me know if this is what you meant...
Reply | Report Abuse | Link to thisIt seems to me the editors should have caught this error. It's the classic fallacy that natural systems work with high efficiency. Given what they're made out of, they're not bad, but nowhere as efficienct as solar panels.
Reply | Report Abuse | Link to thisIt is an article about biotechnology and nanotechnology.
Reply | Report Abuse | Link to thisSo this kind of research can be funded.
The most interesting point of view is that this quantum effect have to be considered in the natural selection of these microbes. Then it is like science fiction.
This case implies that the evolution theory has to take account of all natural sciences. The natural selection is not a food chain as we can imagine.
Well ... in the case of the light food chain at least.
Reply | Report Abuse | Link to thisErrr ... is vitamin D processing needs quantum effects in humans ?! :-))
Reply | Report Abuse | Link to thisMaybe quantum photosenthesis is not just a pat of adapation and evolving life. what if this quantum nature of protein and light was the original organizing force. How do nucleic acids behave if in this quantum manner of light. would a simple organism arrange from innert material throught lights quantum interactions with the components. or maybe over the tremendous span of the "developement" of life -did light itself in its quantum interactions with simple molecules and elements "organize" the living cell -and continue as in our developement today.
Reply | Report Abuse | Link to thisthe subject is light interactions. but as someone mentioned proteins vibrate and if all things do so in quantum -especially carbon compounds -may through quantum interactions (in vitro) develope a simple organism. I hope these guys will look at nucleic acids in this way soon.
Reply | Report Abuse | Link to thisYes -i had some strange picture of a bacteria spontaneously assembling out of molecules. but the clearer picture is arrangement of elements into particles a-prticles into molecules -molecules into higher orginization -and there light crystalized assembly ~from variying sources with their own quantum interactions over the tremendously long time taken to create stomatoliths and such. yeh -that'sit.
Reply | Report Abuse | Link to thisThis is a great article. Nitpicking the authors understanding of the Science involved does nothing to improve the situation. Obviously efficiency is limited by the photon actually falling on the active site. What an amazing trick that would be to capture close to 100% of the energy of the entire solar spectrum falling on a material. The 95% number was a bit misleading if you don't get this. The efficiency here is that 95% of the energy of the photons within the correct wavelengths are converted to chemical bond energy by the microorganism. This would be a good thing if we could build a similar synthetic system. Chemical batteries, eg. storing solar energy as chemical energy is one great way to overcome the limitations of using conventional storage systems. You certainly can't get a 95% efficiency storing the energy produced from a standard solar cell, too much energy wasted as thermal energy, too narrow a frequency response. Thermal storage is certainly valid for that part of the spectrum, but has it's own conversion inefficiencies. Moving away from semi-conductor and into organic technology may be a good idea. There's also the possibility on attaching nanoclusters of semi conductor to organic molecules, and harvesting the energy directly as chemically transformed compounds. Nature has had a billion years of more to fine tune these systems, and it makes total sense to take a look at them.
Reply | Report Abuse | Link to thisYou guys. pick pick pick. I knew it meant absorbed and enterring the system and not just striking the surface. My question is how is this a quantum effect? And I suspect the magnetic field of the photons preceed the presence of the photon and chooses which path is most efficient.
Reply | Report Abuse | Link to thisYou ask, "Where is the quantum effect?" It seems you have never contemplated the wave-particle duality, which is central to Quantum. It is both amusing and frustrating to watch people who are probably fairly intelligent insist on attributing agency to physical processes. Light doesn't "choose" anything, any more than evolution "chooses" the way species will evolve. The basic point of the article was that the photon doesn't follow a single path, it takes both available paths. Because of the duality of the photon, it is both a particle and a wave at the same time. Some propose that this apparent contradiction is actually an artifact of observance, but more likely it is the fundamental nature of the photon/light wave. The double-slit experiment (Young's experiment) demonstrates this nicely.
Reply | Report Abuse | Link to thisPhoton coherence is another way of saying Light is an Electromagnetic wave.
Reply | Report Abuse | Link to thisPhotons do not exist
well, ya'll. glad to have many voices since I think this is brilliantly important.
Reply | Report Abuse | Link to thisremaining somewhat confused, tho not of the opinion that at first appeared-
and the colors continued.
This is why entanglement occurs,some time light is a wave and sometimes its a particle,and sometimes it's both.That's because sometimes it's space=time,and other times it's the fraction of mass called energy and sometimes it's caught in the middle and is both.It's funny plants have been using this phenomena for 100's of millions years with little debate about the duality of light.and it appears that bacteria have been talking with light for much longer than that..
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