1. Joined
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    11 Jan '13 19:032 edits
    http://physicsworld.com/cws/article/news/2013/jan/11/proteins-boost-quantum-coherence-in-bacteria
    "....

    Proteins boost quantum coherence in bacteria

    Jan 11, 2013

    A new theory of how plant photosynthesis involves quantum coherence has been suggested by physicists in the UK, Germany and Spain. This latest research is based on the study of organisms that live deep under the sea yet are able to convert sunlight into energy. The study suggests that molecular vibrations do not destroy the coherence – as previously thought – but rather perpetuate and even regenerate coherence. The discovery could lead to a better understanding how plants achieve as high as 99% efficiency in converting sunlight to energy, as well as the possibility of using nature-inspired designs in quantum devices.

    Until recently, living systems were thought to be "too wet and warm" to rely on delicate quantum properties such as entanglement and coherence. The problem is that these properties decay rapidly via random interactions with things in the outside world, such as vibrating molecules. However, over the past decade physicists have begun to suspect that quantum properties play important roles in biochemical processes – including photosynthesis.

    This latest work was done by Alex Chin (now at Cambridge University) and colleagues at the Institute of Theoretical Physics in Ulm and the Technical University of Cartagena. The team looked at organisms called green sulphur bacteria that live 2000 m below the ocean surface. There is so little sunlight down there that the bacteria cannot afford to lose a single photon – indeed, almost 100% of the light they absorb is turned into food.
    Excited states

    When sunlight hits the surface of the plant, energy is transferred via chains of pigments to a reaction centre, where it is converted into chemical energy. Those pigments are held in place by proteins, which together create pigment–protein complexes, or PPCs. The PPCs effectively act as corridors and the energy itself travels in the form of molecular excited states, or molecular excitons. These excitons are able to move along the PPC by hopping from one molecule to the next.

    In 2007 Graham Fleming and colleagues in the US showed that these excitons exhibit quantum coherence, which means that the excitons may exist simultaneously in a superposition of several quantum states with varying probabilities. Coherence also allows the exciton to explore multiple pathways to the reaction centre simultaneously, ultimately choosing the fastest, most efficient option. As is demonstrated in man-made solar cells (which also rely on excitons), the longer this trip takes, the more likely it is that the energy will dissipate before it reaches its destination.
    Optimizing function

    The presence of quantum effects in photosynthesis surprised both physicists and biologists, and left them wondering how a fragile quantum state could survive in a living organism. More specifically, research groups found that the coherenent states exist for 100-times longer than the coherence time of the energy states of an exciton. Something was helping these wave states survive long enough to ensure the safe passage of nearly 100% of the photon energy that the organisms absorbed.

    This latest research suggests that the answer lies in the proteins in the PPCs, which provide structural support for the pigment molecules. The new calculations reveal that these proteins are more active participants in the transport system than was previously thought. The natural vibration frequencies of the proteins resonate with the exciton waves, and like a parent pushing a child on a swing, the protein structures keep the excitons oscillating without dampening. In fact, the exciton may pass its vibration into the protein structures, which then return it to the exciton, thus restoring its coherence.

    "People have not viewed this protein structure as something that actively helps quantum phenomenon to take place in biological systems," says team member Martin Plenio. "This is really a new way of thinking about things."
    Definitely not noise

    The team's conclusions come from precise analysis of the protein vibrations, using data from Markus Wendling and colleagues in the Netherlands, who in 2000 examined the PPC structures from green sulphur bacteria. Previous efforts to study the protein vibrations used rougher approximations and usually concluded that the vibrations were noise.

    "The main difference in terms of the paradigm for doing this simulation was to not separate the system into the exciton and the environment, but to treat them all together as one large many-body system," says Chin. "We took a completely holistic approach. This makes it very complicated in terms of variables and things that one has to keep track of, which means that computationally it is very tough."

    Understanding these protein structures could assist in building similar structures in quantum devices. If similar structures are used in the conversion of electrical energy to chemical energy, it could shed light on how to mimic photosynthesis's high efficiency rates in man-made solar cells.
    A good hypothesis

    Greg Scholes of the University of Toronto in Canada praises the detailed analysis conducted by the team, and says the conclusions "fit with some of the pieces of the puzzle that have been emerging in more recent experiments".

    While Scholes believes the analysis is "sufficient proof of the idea in principle", he says direct experiments will need to be done to confirm the conclusions. "From that perspective this work really contributes something important. Because it gives us a hypothesis, [and now] we can go and test it," he says.

    ..."





    Now I am confused about some of the comments above regarding energy efficiency of nature's photosynthesis because it first says in the above:

    "...The discovery could lead to a better understanding how plants achieve as high as 99% efficiency in converting sunlight to energy..."

    which, to the best of my knowledge, is completely false! -because, according to all other sources of info I have had so far, the theoretical maximum efficiency of solar energy conversion for nature's photosynthesis is 11% and, in practice, it is much less than this!
    ( see http://en.wikipedia.org/wiki/Photosynthetic_efficiency which says "the theoretical maximum efficiency of solar energy conversion is approximately 11%. 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% of total solar radiation." )

    then it says "...There is so little sunlight down there that the bacteria cannot afford to lose a single photon – indeed, almost 100% of the light they absorb is turned into food. ..."
    which, again, seems to completely contradict what I think I know.

    Can anyone explain that? have they simply got their basic facts wrong in the http://physicsworld.com/cws/article/news/2013/jan/11/proteins-boost-quantum-coherence-in-bacteria link? if not, why the apparent contradiction with what the http://en.wikipedia.org/wiki/Photosynthetic_efficiency link says? -I mean, one says the max is ~99% and the other says it is ~11% and they cannot be both right!?
  2. Subscribersonhouse
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    12 Jan '13 18:121 edit
    Originally posted by humy
    http://physicsworld.com/cws/article/news/2013/jan/11/proteins-boost-quantum-coherence-in-bacteria
    "....

    Proteins boost quantum coherence in bacteria

    Jan 11, 2013

    A new theory of how plant photosynthesis involves quantum coherence has been suggested by physicists in the UK, Germany and Spain. This latest research is based on the study of organisms that s ~99% and the other says it is ~11% and they cannot be both right!?
    Maybe the increased efficiency is due to the exact protein they are studying. If it is true, near 100% utilization of photons then it is the result of evolutionary changes not needed by lifeforms close to the surface where the total irradiation is a lot higher.

    Time will tell if anything comes of it.

    But can you imagine, 100% photocells? That would change everything. There is 1300 watts per square meter of solar energy on top of the atmosphere and something like half of the gets to the surface on average but even so, 600 watts per square meter as opposed to the 50 watts we get now?(for one square meter of PV cells) It would make solar powered cars more of a reality among other things. I think the solar racers are getting maybe 1 kw max and it looks like they are putting up something like 4 square meters of cells. They are already getting up to 100 Km/hr out of just that. To say nothing of the great gas milage🙂
  3. Joined
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    12 Jan '13 21:262 edits
    Originally posted by sonhouse
    Maybe the increased efficiency is due to the exact protein they are studying. If it is true, near 100% utilization of photons then it is the result of evolutionary changes not needed by lifeforms close to the surface where the total irradiation is a lot higher.

    Time will tell if anything comes of it.

    But can you imagine, 100% photocells? That would ch ...[text shortened]... y are already getting up to 100 Km/hr out of just that. To say nothing of the great gas milage🙂
    Maybe the increased efficiency is due to the exact protein they are studying


    I think you are probably right but not sure and that bothered me so much that I decided to get at the bottom of this by adding my own comment in the form of questions about this at the http://physicsworld.com/cws/article/news/2013/jan/11/proteins-boost-quantum-coherence-in-bacteria link which you can see at the bottom if you go there.

    But can you imagine, 100% photocells?


    yes! Wouldn’t that be just fantastic! it would mean, among other things, most of if not all our energy, at the very least for mains electricity, could easily come from solar power (the problem of the required energy storage to make that work is not insurmountable)
  4. Joined
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    13 Jan '13 11:483 edits
    Originally posted by sonhouse
    Maybe the increased efficiency is due to the exact protein they are studying. If it is true, near 100% utilization of photons then it is the result of evolutionary changes not needed by lifeforms close to the surface where the total irradiation is a lot higher.

    Time will tell if anything comes of it.

    But can you imagine, 100% photocells? That would ch ...[text shortened]... y are already getting up to 100 Km/hr out of just that. To say nothing of the great gas milage🙂
    But can you imagine, 100% photocells?


    I have just found a piece of info that, if I am interpreting correctly, means such high efficiency for a photocells MUST be possible!:

    http://www.bio4bio.dk/~/media/Bio4bio/publications/Review_of_algae_biomass_for_energy_SW_CF_April2010.ashx
    “...
    The efficiency by which the energy from the protons is transferred to electrons within the plant photosynthesis is very high and for simplicity we can
    assume it to be 100%. With the single carbohydrate having 1/6 of the glucose energy content i.e. 467 kJ
    mol‐1, the quantum limit of the photosynthetic efficiency is 11.6 %.
    ...”

    So, if I understand the above correctly, it says that, out of the light energy absorbed of the wavelengths that could potentially be used for photosynthesis, near 100% is converted to energy of electrons and it is only the energy transfer from the energy of the electrons to organic chemical energy that accounts for most of the loss of energy efficiency.
    But, surely, that transfer of light energy to energy of the electrons with near 100% efficiency could be viewed as being equivalent to converting light energy into electric energy with near 100% energy efficiency thus nature here has given us absolute POOF here that it IS physically possible to convert light energy to electric energy with near 100% efficiency?
    So, therefore, If that is correct, we can extrapolate from that to deduce there MUST exist a possible design for an electric generating photocell that is near 100% efficient!? -and, if so, it is surely just a matter of time before we obtain it!
  5. Subscribersonhouse
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    14 Jan '13 08:27
    Originally posted by humy
    But can you imagine, 100% photocells?


    I have just found a piece of info that, if I am interpreting correctly, means such high efficiency for a photocells MUST be possible!:

    http://www.bio4bio.dk/~/media/Bio4bio/publications/Review_of_algae_biomass_for_energy_SW_CF_April2010.ashx
    “...
    The efficiency by which the energy from the proto ...[text shortened]... at is near 100% efficient!? -and, if so, it is surely just a matter of time before we obtain it!
    That's the rub, how much time. It could be decades.
  6. Subscribersonhouse
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    14 Jan '13 15:381 edit
    Originally posted by sonhouse
    That's the rub, how much time. It could be decades.
    I just found an article about multi-junction (multi-bandgap) PV cells. There is one sentence that says the maximum theoretical efficiency of an infinite bandgap layer material is 87%. They are trying for 50% cells now. They claim the max efficiency now is 44% for solar concentrated cells. That takes lenses or concentration reflectors so the system is a bit more complex, would require sun tracking equipment for sure.

    http://phys.org/news/2013-01-multi-junction-solar-cell-efficiency-barrier.html
  7. Joined
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    14 Jan '13 19:245 edits
    Originally posted by sonhouse
    I just found an article about multi-junction (multi-bandgap) PV cells. There is one sentence that says the maximum theoretical efficiency of an infinite bandgap layer material is 87%. They are trying for 50% cells now. They claim the max efficiency now is 44% for solar concentrated cells. That takes lenses or concentration reflectors so the system is a bit ...[text shortened]... ment for sure.

    http://phys.org/news/2013-01-multi-junction-solar-cell-efficiency-barrier.html
    Yes, they said:

    “...In theory, an infinite-junction cell could obtain a maximum power conversion percentage of nearly 87 percent. ...”

    BUT, what they don't mention in the above is that the “In theory” part above refers to a theory based on a number of severe constraints/assumptions of what design features the photocell would have and, in particular, assumes it must be made of conventional semiconductors. What if it doesn’t? What if the photon-absorbing part is made of molecules like those complex bacterial proteins that involves subtle quantum coherence to allow highly efficient conversion of photon-energy to electron-energy (except designed to be without the water being present and it not necessarily being proteins although it probably would still involve extremely complex molecules)? Those proteins are nothing like the crude current man-made conventional semiconductors! And I think it is just a matter of time before molecular science catches up with nature and it is this that makes me so optimistic we can do so much better than even, say 'nearly 87%'.

    But, as you said, the rub is how long -but that's the only rub I think.

    (Incidentally, not a bad article)
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