Quantum Evidence 4

Further summaries and reviews of papers relevant to evidence of quantum coherence/entanglement in biological matter

1.) Microtubule super-lattices - Stuart Hameroff - Reply to Reimers et al attack on Penrose/Hameroff model

2.) Excitation of vibrations in microtubules in living cells - Pokorny, J. - Paper and experimental evidence argues for likelyhood of excitations in microtubules.

3.) Electrical vibrations of yeast cell membrane - M. Cifra & J. Pokorny et al - Describes experiments measuring oscillations in living cells

4.) Local nanomechanical motion of the walls of yeast cells - Pelling, A. et al - Oscillations in yeast cells possibly linked to microtubule motor proteins

5.) Dynamic entanglement in oscillating molecules - Cia, J. et al - Oscillating molecules and a noisy environment could reset quantum entanglement.

6.) Brain Coherence and Entanglement in the 21st Century - Derived from various referenced sources - Discusses the implications of studies of quantum coherence and quantum entanglement in living matter since 2007.

7.) Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature - Akihito Ishizaki & Graham Fleming - Investigates quantum coherence in photosynthetic protein at physiological temperatures.

8.) Quantum coherence in living organisms at room temperature - Implications for quantum computing and quantum consciousness - Elsabetta Collini et al - Study demonstrates quantum coherence in protein at room temperature, contrary to previous view that this was impossible.

1.)

Microtubule super-lattices (reply to Reimers et al)

Stuart Hameroff

University of Arizona

In the 1960s and 1970s Frohlich (1. Frohlich, 1968) proposed the possibility of Bose-Einstein condensation (particles locked in phase as a single quantum object) in certain biomolecules. In a recent papers (2. Reimers et al, 2009) the authors describe three types of Frohlich condensation , weak, strong and coherent. They estimate that strong and coherent condensation are not feasible in microtubules, but that weak condensation is feasible. They state that (3. Pokorny, 2004) has experimentally demonstrated weak Frohlich condensation in microtubules. Reimers et al claim that the Penrose/Hameroff quantum consciousness model requires strong or coherent condensation, and that the model can therefore be refuted.

Hameroff takes issue with Reimers on two counts. Firstly, he suggests that weak condensation may be able to support the Penrose/Hameroff model, and secondly, he denies Reimers claim that strong or coherent condensation is not feasible in microtubules. He criticises Reimers et al for basing their study on just a linear chain of tubulin oscillators. Microtubules are cylindrical lattices, rather than one dimensional chains or flat two dimensional lattices that Reimers et al are claimed to have pre-supposed.

A 2006 study (4. Brangwynne et al, 2006) demonstrates how microtubules can bear the loads within cells because of lateral reinforcement. The relatively rigid microtubules are compressed by the contractile actin and other filaments to form a network of structural support for the cell. Hameroff claims that this compression of microtubules within living cells suits them to vibrational resonances. He further claims that this along with a geometry that ensures that signals within the microtubule lattice interact makes it a substantial error to compare a free standing chain or lattice to the conditions prevailing in microtubules.

Hameroff also refers back to the work of (5. Samsonovich et al, 1992). This paper considered Frohlich coherence in a microtubule. The resonance of phonon energy was distributed on a microtubule lattice in periodic patterns, or super-lattices overlying the microtubule lattice. Some of such patterns match the experimentally observed locations of the attachment points of microtubule associated proteins (MAPs); these latter control the architecture and function of the cells. Hameroff claims that the regularity of these super-lattices on microtubules is difficult to explain except by non-local effects.

The Reimers et al paper seems to bear a resemblance to the many earlier refutations of the Penrose/Hameroff model that have subsequently turned out to be based on rather simplistic approaches to a complex question. However, it should be expected that the Reimers paper like the earlier (6. Tegmark, 2000) paper will be widely quoted and praised by the mainstream consciousness community. That said the Reimers paper concedes the main argument against quantum consciousness, which is that quantum features could not survive in brian proteins, by admitting feasibility of condensates in microtubules. This retreat may come in the face of Engel et al's evidence for quantum coherence in photosynthetic protein.

References:-

1.) Frohlich, H. (1968) - Long-range coherence and energy storage in biological systems - International Journal of Quantum Chemistry 2, 641-649

2.) Reimers et al, (2009) - Weak, strong and coherent Frohlich condensation - Proceedings of the National Academy of Sciences

3.) Pokorny, J. (2004) - Excitations of vibrations in microtubules in living cells - Bioelectrochemistry, 63, 321-6

4.) Brangwynne et al (2006) - Microtubules can bear enhanced compressive loads - Journal of Cell Biology, 173, 733-41

5.) Samsonovich, A., Scott, A.. & Hameroff, S. (1992) - Transitions in microtubules: Implications for intracellular information processing - Nanobiology, 1, 457-68 .

6.) Tegmark, M. (2000) - The importance of quantum decoherence in brain processes - Physica Rev E, 61, 4194-4206

Collini, E. & Scholes, G. (2009) - Excitons surf along conjugated polymer chains - Science, 323, 369-73

Engel, G. et al, (2007) - Evidence for wavelike energy transfer through quantum coherence in photosynthetic bacteria - Nature, 446, 782-6

2.)

Excitation of vibrations in microtubules in living cells

J. Pokorny

Academy of Sciences of the Czech Republic P. Bioelectrochemistry, 63, (2004), pp. 321-6

Pokorny's paper is regarded as favourable to the Penrose/Hameroff model in that it argues that an ion layer and bound water should allow energy created inside microtubules to drive excitations. Such a mechanism of excitation in microtubules is central to Hameroff's part of the Penrose/Hameroff quantum consciousness model, but has been widely rejected as impossible in the conditions of biological cells.

The paper starts by stating that the polar (opposite electric charge) character of biological objects suggests that there are longitudinal oscillations. The author's calculation show that some forms of such energy are not thermalised, but are instead condensed into a pattern of oscillations. In this context, the structure of the cell's cytoskeleton, which is based on microtubules, is stated to satisfy the basic requirements for an oscillating electric field (1. Pokorny, J, 1999). Later work by the author (2. Pokorny, J, 2003) confirmed the possibility of oscillations despite the existence of surrounding water.

The situation at the surface of the microtubules is the central theme of this paper. A study by Foster and Baish (2000) claimed to show that the damping of oscillations by surrounding water made it impossible for such vibrations to survive in microtubules. The author criticises their approach for failing to take account of an ionic charge layer or cylindrical envelope around the microtubule. It is thought likley that there is a similar charge layer between the inner wall of the microtubule and the hollow cavity in the centre, which may also be filled with cytosol. The ions are surrounded by bounded molecules, and electrically charged proteins may also be involved. A slip layer forms between the microtubule and the surrounding cytosol, because microtubules are easily deformed at even low stress.

Taking the cytosol as a whole, it is thought that the damping effects of water on oscillation (viscosity) is not much different from ordinary water, but that near surfaces, such as the surfaces of microtubules, there may be layers of ordered water as much as 200 nm thick. The effects of the ion layer and bound water would be to reduce viscosity, and thus promote the survival of excitations within the microtubule. Losses to viscosity in the inner cavity of the microtubule might be particularly low, as it is thought that all the water in this area could be ordered.

The microtubules are supplied with energy by the hydrolysis of guanosine triphosphate (GTP) to diphosphate (GDP), and a considerable amount of this energy is stored in the microtubule. This may serve to increase tension in the microtubule, and to excite coherent waves. Polarisation waves may arise in the direction of the microtubule axis, and it is suggested that there may be a high intensity electric field near the outer surface of the microtubule and also near the surface next to the internal cavity.

The author argues for an overall picture of energy supply and the possibility of excitation. Energy is generated at one end of the microtubule, and this dominant near zone electrical component can be involved in the orientation of macromolecules and the direction of polymer structures and polymerisation. The amount of the energy supply is deemed sufficient for excitation, even after taking account of losses as a result of being immersed in liquid.

The ideas put forward in this paper were experimentally tested by (3. Pokorny, J. et al, 2001). In this experiment recorded electromagnetic emissions from cells were regarded as promising, although more accurate tests would be needed to show whether the emissions came from microtubules rather than other parts of the cell.

References:

1.) Pokorny, J. - Conditions for coherent vibrations in cytoskeletons - Bioenergy. 48, (1999), pp. 267-71

2.) Pokorny, J. - Viscous effects on polar vibrations in microtubules - Biol. Med., 22, (2003), pp. 15-19

3.) Pokorny, J. et al - Electromagnetic activity of yeast cells - Electromagnetobiology, 20, (2001), pp. 371-96

3.)

Electric vibrations of yeast cell membrane

M. Cifra & J. Pokorny et al

Academy of Sciences of the Czech Republic and Czech Technical University

Piers Online, vol. 3, No. 8, 2007

The paper starts by referring to Frohlich's fondational proposal (1. Frohlich, 1968) that there could be electrically polar longitudinal vibrations in biological systems, generating an internal electromagnetic field. This hypothesis is frequently mentioned in quantum consciousness discussions, but until the last few years, it did not appear to have been much followed up in terms of experimental studies.

This paper refers to experiments by Pelling et al (2 & 3. Pelling et al, 2004 & 2005). Studies with an atomic force microscope detected oscillations in yeast cells. Oscillations at a single frequency have been detected on the yeast cell wall and multiple frequencies elsewhere. Both types of oscillation ceased after the addition of a metabolic inhibitor, which suggested to the experimenters that the oscillation was based on cellular metabolism.

The authors of this paper propose three ways by which the energy to drive this oscillation could be generated. 1.) Release of energy stored in microtubules by hydrolysis of guanosine triphosphate to diphosphate. 2.) Motor proteins 'crawling' along microtubules. 3.) Vibrational energy released from mitochondria. The authors suggest that microtubules can be considered as vibrating chains of dipoles that generate an oscillating electrical field. The cytoskeleton of the cells comprises microtubules, microtubule associated proteins, and actin filaments. The authors point out that actin flaments are polar structures in the same way as microtubules and produce energy through the hydrolysis of ATP, which is analogous to energy production found in microtubules.

The authors give a detailed description of their experimental set up. The results of preliminary measurements showed electrical oscillations of yeast cells in the 1280-1400 Hz bandwidth. These findings are stated to be consistent with the original Frohlich postulate of electrical polar longitudinal vibrations in biological systems. The authors acknowledge some limitations on experimental accuracy, but nevertheless go on to say that the existence of such an internal magnetic field in living cells has far reaching implications for the structural organisation of organisms. It is clear that this a tranche of experiments in recent years are chipping away at the mainstream stance towards microtubules in particular and quantum features in living tissue in general

References:-

1.) Frohlich, H. - Bose condensation of strongly excited logitudinal electric modes - Phys. Letters Ser. A., vol 26, (1968), pp. 402-3

2.) Pelling, A. et al - Local nanomechanical motion of the cell wall - Science, vol. 305, pp. 1147-50

3.) Pelling, A. et al - Time dependency of the frequency and amplitude of the local nanomechanical motion of yeast - Nanomedicine, vol. 1, (2005), pp. 178-83

Jeline, F. & Pokorny, J. et al - Measurement of eelctromagnetic activity of yeast cells - Radioengineering, vol, 16, No. 1, (2007), pp. 36-9

4.)

Local nanomechanical motion of the walls of yeast cells

Pelling, A. et al P. Science, vol. 305, (2004), pp. 1147-50

Introduction: This paper uses the results of experiments with yeast cells to suggest that motor proteins, possibly including microtubule motor proteins, are involved with observed nanomechanical oscillations in these yeast cells. The authors consider that their work has revealed a new nanomechanicla aspect of cells.

The paper starts by stating that biological processes inside the living cell rely on the nanomechanical properties of cellular substructures and of the cell membrane itself. These can be studied by means of atomic force microscopes that have shown the existence of periodic nanomechanical processes in yeast cells. In an experiment with yeast cells the motion of the cell body was oscillatory. The observed frequencies of the oscillation at given temperatures were similar to within 5% in different cells.

The paper discusses whether the mechanism for these oscillations is wholly or partly based on random Brownian motion, or whether it is a metabolic process. Yeast cells were treated with sodium azide, a metabolic inhibitor that switches off ATP energy production in mitochondria. Oscillatory behaviour was not observed in those cells that had been treated with sodium azide. The dependence on both temperature and metabolic state is taken by the experimenters to indicate that the nanomechanical motion is biologically driven.

The energy involved in this is consistent with the involvement of motor proteins, including the microtubule motor proteins, kinesin and dynein. Operating speeds for these proteins are comparable with those for the nanomechanical measurements that the experimenters have observed in yeast cells. The authors observations suggest that many motor proteins are involved in concerted action to produce the observed oscillations. Spontaneous driven oscillations have been observed in muscle and auditory cells, where molecular motions are coupled to the environment by microtubules or other cytoskeletal filaments. The existence of such concerted motor protein is taken to support the authors' argument that metabolically driven nanomechanical activity occurs in yeast cells.

It is suggested that the observed motion may be part of a communication path or pumping mechanism to supplement passive diffusion of nutrients, or to drive the transport of chemicals across the cell wall. More refined methods are needed to study mammalian cells, but the authors think that their findings have revealed a new nanomechanical aspect to cells.

5.)

Dynamic entanglement in oscillating molecules

Cia, J. et al - Institute of Theoretical Physics, University of Innsbruck

arXiv:0809.4906v1 [quantum-ph] 29 Sep. 2009

INTRODUCTION: The authors' model suggests that although static entanglement could not persist in biological conditions, the combination of molecular oscillation and environmental noise could result in the repeated resetting of quantum entanglement. Such a possibility is important for some models of quantum consciousness and notably for the Penrose/Hameroff model.

The authors emphasise the difference between solid state physics and biology, in which movement within an organism has to be taken into account. In the case of protein, the key building block of organisms, its functioning requires conformational changes, as in the folding of protein. These functions involve time-dependent quantum interactions, including those of hydrogen bonds, that are switched on and off as the protein molecule changes its shape. These changes are essential for the biological functions of the proteins. These interactions are subject to the considerable noise from the fluctuations of surrounding dipole fields, and have therefore traditionally been dealt with in terms of classical physics. The authors think that for adequate results, it may be necessary to treat these interactions quantum mechanically.

In particular, their model suggests that while while a static entanglement could not survive in the conditions of the brain, it might be possible for fresh entanglements to be generated. The effect of the environment on the motion of biomolecules is complex, and not yet fully understood. According to the authors' calculations, entanglement can persistently recur in an oscillating molecule, even if the environment is too hot for static entanglement. The oscillation of the molecule combined with the noise of the environment is suggested to repeatedly reset entanglement. This non-equilibrium quantum system is driven by oscillatory motion that prevents it from reaching thermal equilibrium, with environmental noise and driven motion playing a constructive role as a reset mechanism. It is stressed that the oscillating molecule is not in thermal equilibrium, and that it absorbs heat from the environment. The authors claim that their model could be simulated by means of trapped ions.

6.)

Brain Coherence and Entanglement in the 21st Century

Derived from various sources referenced below

The debate over quantum coherence and entanglement in the brain and their possible connection to consciousness may have been moved into a new stage by the discovery that quantum coherence has a functional role in the transfer of energy within proteins, the basic building blocks of living cells (1. Engel et al, 2007). Most importantly, it knocks a hole in the central argument against quantum consciousness, which has been the claimed impossibility of quantum coherence being sustained for any useful period in biological matter. At the same time, it moves the discussion of what sort of coherent features could support consciousness on from a phase of pure theorising, to a phase in which ideas can be related to features that have been shown to exist in biological matter.

In the nearly three years since Engel's study was published in Nature, there has been almost no discussion of the possible significance of this finding in relation to consciousness. Anyone familiar with mainstream consciousness studies in the last ten years, where the very mention of quantum consciousness produces a braying chorus of 'fringe' and 'pseudoscience', will not be surprised by the absence of constructive comment from that direction. Engel and other researchers in the field of quantum coherence in protein are not involved in researching consciousness, and would probably not improve their chances of funding, if they suggested there was any connection to consciousness. More disappointing is the relative lack of discussion within the very limited realm of quantum consciousness studies.

Hameroff has referred to Engel et al as evidence for quantum coherence in the brain, but does not appear to have discussed the large difference between the time to collapse in Engel's study and the much longer time in the Orch OR model. Georgiev (2. ) criticises Hameroff's model for not being synchronised with the 10-15 picosecond (picosecond=10^-12 seconds) timescale, which governs much of the activity in protein and enzymes, but again does not really engage with the Engel study.

I am reluctant to cross the line from merely commenting on studies, to making more or less original comments, but confronted with an effective research vacuum, I feel forced to do this to a limited degree. Hameroff, and Georgiev at least sometimes, relate to models based on Penrose's idea of objective reduction (OR), in which the self-collapse of quanta that have not interacted with the environment gives access to understanding or consciousness as a fundamental property of spacetime. In this model, the important question is whether this objective collapse or reduction occurs within a timescale that could be relevant to neural processing. A single quanta in isolation might not decohere for millions of years. Some more substantial quantum system is needed to make this model of quantum consciousness plausible. This is where the possibility of the entanglement of many quanta, giving a larger, more energetic, quantum feature, and thus a longer time to reduction that is more in line with neural processes becomes interesting.

Engel et al studied photosynthesis in green sulphur bacteria. Unpromising as this may sound, much the same principles apply across all multicellular living tissues, and this means that the nature of processing in these complexes could be relevant to what happens in neurons. The photosynthetic complexes (chromophores) in the bacteria are tuned to capturing light and transmitting its energy to long-term storage areas. It should be stressed that in this system, photons (the light quanta) only provide the initial excitation, and the coherence and entanglement discussed here involves electrons in the protein.

It is the energy transfer mechanism that is of interest in this case. Traditionally, this had been analysed in terms of classical physics. However, the Engel study documented the dependence of the energy transport on the spatially extended properties of the wave function of the photosynthetic complexes. In particular, the timescale of the quantum coherence observed was much longer than would normally be predicted for a protein environment, with a duration of at least 660 femtoseconds (femtosecond=10^-15), nearly three times as long as the normally predicted times of 250 femtoseconds. In the latter case, rapid destruction of coherence would prevent it from influencing the system.

Engel does not offer much discussion of the reason for this delay in decoherence, but it could be crucial if this process is related to quantum consciousness. This particular feature should be a wake up call for students of quantum consciousness, since almost the only rational debate in this area has centred on whether the time to quantum decoherence in living matter could be long enough for it to be relevant to neural processes. The delay from 250 to 660 femtoseconds hints at some kind of protection or screening of coherence, analogous to the screening argued for by Hameroff.

Engel further points out that there is a considerable adaptive advantage to using quantum coherence, in that it allows the photosynthetic complexes to sample a vast number of different routes, in order to find the most efficient one. Engel views the system as performing a single quantum computation, sensing many states simultaneously and selecting the correct answer. This process is analogous to Grover's algorithm. The involvement of quantum coherence explains the extreme efficiency of the system. Engel also considers the possibility that non-local entanglement is involved in the quantum activity within the chromophores. Some earlier models had recognised coherence between donor and acceptor electrons, but Engel says that to account for the unexpectedly long-lived coherence it is necessary to accept that protein has an active role in the coherence. Towards the end of his paper, Engel stresses that his findings may have further implications in that protein may itself produce the structures that in turn give rise to further coherence transfer.

Other recent studies give support to Engel's work. Collini & Scholes (3. 2009) view the chromophores as a situation in which protein can protect coherence from the environment. In a paper by Fleming and co-workers (4. 2007) that relates to the earlier work by Engel, the authors look at evidence that a collective long-range electrostatic response of protein to electronic excitation is responsible for sustained quantum coherence. The protein environment both protects coherence, and increases the efficiency of energy transport.

In a 2009 paper, Sarovar et al (5.) examined the subject of possible quantum entanglement in the photosynthetic complexes discussed above. Entanglement carries the possibility of a large number of particles acting as a single quantum feature, and having a time to objective reduction that could have some bearing on neural processing. The paper starts from the base of quantum coherence between the spatially separated chromophore molecules found in these systems. The entanglement examined is the non-local correlation between the electronic states of spatially separated chromophores. Coherence is a necessary and sufficient state for entanglement to exist. The coherence properties of the photosynthetic complex reflect the interplay of the protein with the decoherence effects of the environment.

Ishizaki and Fleming (2009) developed an equation that allows modelling of this system. Where this deals with the initial sites to be excited by the light energy, the initial entanglement rapidly decreases to zero, but then increases again after about 600 femtoseconds. This is thought to be a function of the entanglement of the initial sites being transported and localised at other sites, but remaining coherent at these other sites, from which further entanglement can subsequently resurge. Interestingly, the timescale of entanglement between the different sites in the photosynthetic complex is much longer than for coherence. The coherence is 660 femtoseconds or greater, while entanglement can last for about 5 picoseconds at the relatively low temperature of 77 Kelvin or 2 picoseconds at room temperature. The authors regard this as remarkable in the conditions of biological matter. This study is only the result of modelling, but is considered to be experimentally verifiable. The few picosecond timescale for entanglement suggested in Sarovar's paper is any case getting into something like the same ballpark as the 10-15 picoseconds relevant to much protein and enzyme activity. Other studies appear to confirm the existence of picosecond timescales for entanglement in chromophores. It is not clear to the authors that entanglement is actually functional in chromophores. Coherence appears to be sufficient for very efficient transport of energy, and entanglement may be only a by-product of coherence. At the same time, it is speculated that such entanglement might provide a lead in the development of quantum technologies.

Also in a 2008 paper (7.), Cia et al looked at the possibility of quantum entanglement in the type of system studied in the Engel paper. Cia takes the view that entanglement can exist in hot biological environments. The paper draws attention both to a paper in Nature demonstrating quantum tunnelling by enzymes (8. Ball, 2004), and to the Engel paper referred to above. Biologists have been generally sceptical as to the possibility of quantum entanglement in living matter. However, Cia says that such thinking is based on the assumption of thermal equilibrium, whereas biological systems are far from thermal equilibrium. Cia points out the conformation of protein involves interactions at the quantum level. These are usually treated classically, but Cia wonders whether a proper understanding of protein dynamics does not require quantum mechanics. It is said not to be clear, whether or not entanglement is generated during the motions of protein, but that entanglement might have important implications for the functioning of protein.

The model studied by the Cia et al paper suggests that while a noisy environment, such as that found in biological matter, can destroy entanglement, it can also set up fresh entanglement. It is argued that entanglement can recur in the case of an oscillating molecule, in a way that would not be possible in the absence of this oscillation. The molecule has to oscillate at a certain rate relative to the environment to become entangled. This allows for entanglement to emerge, but this would normally also disappear quickly. Something extra is needed for entanglement to recur or persist. It is suggested that the environment, which is normally viewed as the source of decoherence, can play a constructive role in resetting entanglement, when combined with classical molecules. Environmental noise in combination with molecular motion provides a reset mechanism for entanglement. The suggestion that entanglement can exist by resetting itself in a noisy environment, and the further suggestion of possible entanglement in Engel's photosynthetic structures point to the possibility that relatively large structures are entangled, with times to objective reduction that could be relevant to neural activities.

Following the recent papers discussed above, the debate on quantum coherence in living tissues has moved to a new stage. We now have definite evidence of functional quantum coherence in living matter, and also modelling that makes it likely that there is also quantum entanglement in living matter. In looking for a possible mechanism for quantum consciousness, the principle of Occam's razor suggests that that we should work with existing evidence, rather than more speculative possibilities. In the present state of knowledge, the findings with photosynthetic protein appear to be a more promising basis than either the very ambitious timescales of the Hameroff model, which put heavy demands on the possible amount of microtubule screening, or the less ambitious timescales suggested by Jibu and Yasue for quantum brain dynamics, which, however, relate to the water dipoles in a way not immediately seen to be relevant to the actually demonstrated coherence/entanglement in photosynthetic complexes. The structures described do not immediately provide a linking mechanism to the various timescales to which theorists have attempted to link coherence or entanglement in the brain, but it is not possible to match all these features, which have included Libet's half second, the gamma synchrony and the processing timescales of proteins and enzymes. The studies discussed above suggest there is an existing means by which quantum consciousness might be supported in the brain. It is possible that once established there quantum consciousness can influence other features such as the gamma synchrony by further intermediate steps. There appears to be a good argument for concentrating the attention of such study that is given to quantum consciousness in this area.

References:-
1.) Engel et al (2007) - Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems - Nature, 446, pp. 782-6 doi:10.1038
2.) Georgiev, D. (2004) - Bose-Einstein condensation of tunnelling photons in the brain cortex as a mechanism of conscious action
3.) Collini, Elisabetta & Scholes, G. (2009) - Coherent intrachain energy in migration in a conjugated polymer at room temperature - Science, vol. 323 No. 5912 pp. 369-73, DOI: 10.1126
4.) Lee, H., Cheng, Y. & Fleming, G. (2007) - Coherence dynamics in photosynthesis: Protein protection of excitonic coherence - Science, 316, 1462
5.) Sarovar, M. et al - Quantum entanglement in photosynthetic light harvesting complexes
6.) Ishizaki, A. & Fleming, G. (2009) - On the adequacy of the Redfield equation and related approaches to the study of quantum dynamics in electronic energy transfer - Journal of Chemical Physics
7.) Cia, J. et al, (2009) - Dynamic entanglement in oscillating molecules - arXiv:0809.4906v1 [quant-ph] P. 9.) Ball, (2004) - Nature, 431, p. 792

7.)

Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature

Akihito Ishizaki & Graham Fleming

University of California, Berkeley & Lawrence Berkeley National Laboratory

PNAS, 7 August 2009

INTRODUCTION: Relative to the study of quantum coherence in photosynthetic protein, this paper builds on the earlier work of Engel et al in looking at the question of quantum coherence at physiological temperatures. The authors' investigation indicates that coherence may be sustained for a significant length of time at these temperatures, and possibly almost as long as at the cyrogenic temperatures used in the Engel study.

This paper builds on the work of Engel et al (2007) [1.] in studying quantum coherence in photosynthetic proteins. The purpose of the paper is to study the action of quantum coherence at the physiological temperature of 300 Kelvin, rather than the cryogenic temperature of 77 Kelvin use in the Engel study. Theoretical investigation in this paper reveals that quantum wavelike motion can also persist at physiological temperatures. It is suggested that this may be involved in the transfer of energy from the light-harvesting antenna to the reaction centre complex in photosynthetic proteins. Quantum coherence may serve to overcome local energy traps, and thus aid the efficient trapping of electronic energy by the pigments.

This study refers to the Fenna-Matthews-Olson (FMO) pigment-protein complex found in low light-adapted green sulphur bacteria. The FMO is situated between the chlorosome antenna and the reaction centre, and its function is to transport energy harvested from sunlight by the antenna to the reaction centre. The FMO complex is a trimer of identical sub-units, each comprised of seven bacteriochlorphyl (BChl) molecules. This structure has been extensively studied. Quantum coherence in the structure has been assumed to decohere too rapidly to be relevant to its function, until the Engel et al study in 2007. In the Engel et al study, the observed coherence lasts for a similar timespan to the excitation energy transfer (EET). This implied that the excitation energy transfer passed through the FMO complex by means of quantum coherence, rather than by involving a classical process. Long-lasting quantum coherence has also been observed in purple bacteria (2. Lee et al, 2007). It is suggested that quantum coherence is responsible for the remarkably high efficiency of EET transfer in photosynthetic bacteria.

However, the Engel and Lee studies were performed at low temperatures, whereas quantum coherence becomes more fragile at higher temperatures, because of the higher amplitude of environmental fluctuations. In this paper, the equation supplied by the authors suggest that coherence could persist for several hundred femtoseconds even at physiological temperatures of 300 Kelvin. EET dynamics are considered within one sub-unit of the FMO, as inter sub-unit coherence would be expected to be too rapidly destroyed by the environment, to be relevant to energy transfer. Each unit comproses 7 BChl molecules. BChl 1 and 6 are orientated towards the chlorosome antenna, and are the initially excited pigment, and BChl 3 and 4 are orientated towards the reaction centre. Even at the physiological temperatures, quantum coherence can be observed for up to 350 femtoseconds in this structure. This suggests that long-lived electronic coherence is sustained among the BChls, even at physiological temperatures, and may play a role in the high efficiency of EET in photosynthetic proteins.

BChl 1 and 6 are seen as capturing and conveying onward the initial electronic energy excitation. Quantum coherence is suggested to allow rapid sampling of pathways to BChl 3 that connects to the reaction centre. If the process was entirely classical, trapping of energy in subsidiary minima would be inevitable, whereas quantum delocalisation can avoid such traps, and aid the capture of excitation by pigments BChl 3 and 4. BChl 6 is strongly coupled to BChl 5 and 7, which are in turn stongly coupled to BChl 4, ensuring transfer of excitation energy. Delocalisation of energy over several of the molecules allows exploration of the lowest energy site in BChl 3.

The study predicts that qauntum coherence could be sustained for 350 femtoseconds, but if the calculation is adjusted for a possible longer phonon relaxation time, this could extend to 550 femtoseconds, still at physiological temperatures. A study be Collini & Scholes (3. 2009) supports the idea of long lived quantum coherence at room temperature.

References:-
1.) Engel et al, (20070 - Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems - Nature, 446, pp. 782-6
2.) Lee et al, (2007) - Coherence dynamics in photosynthesis: Protein protection of excitonic coherence - Science, vol. 316
3.) Elizabetti Collini & Gregory Scholes, (2009) - Coherent intrachain energy migration in a conjugated polymer at room temperature - Science, vol. 323, no. 3912, pp. 369-73, DOI: 10.1126/science. 1164016

8.)

Coherently wired light-harvesting in photosynthetic marine algae at ambient temperatures

Elisabetta Collini, Cathy Wong, Krystyna Wilk, Paul Curmi, Paul Brumer & Gregory Scholes

Universities of Toronto, New South Wales and Padua

Nature, 463, pp. 644-7, 4 February 2010 doi:10.1038/nature08811

INTRODUCTION: This low-key paper may in time come to be seen as one of the decisive studies of the 21st century. The paper shows that room temperature quantum coherence can occur in biological matter. In 2007, Engel et al had shown that coherence was possible in organic matter, but this was only demonstrated at very low temperatures, whereas the Collini study demonstrates similar activity at ambient temperature. The paper and related commentaries makes no mention of consciousness, although a relevance to quantum computing is suggested, which is a possible step towards discussing consciousness. The main plank of the arguments against quantum consciousness relates to the speed of decoherence in biological matter being too quick for coherence to be relevant to processing, particularly neural processing, in such matter. This argument looks to have been substantially undermined by the recent study.

Antenna proteins are an essential part of the photosyntetic process, which absorbs light and transmits the resulting excitation between molecules to a reaction centre. Recent research has concentrated on determining the mechanisms that support a very high level of efficiency in this energy transport. Light-harvesting antennas are comprised of eight pigment-molecules, with different pigments absorbing different frequencies of light. The route the energy takes across the molecule is important in terms of energy efficiency.

Studies have documented the fact that light-absorbing molecules in some photosynthetic proteins transfer energy according to quantum mechanical rather than classical laws even at ambient temperature. This contradicts the 20th century dogma that long-range quantum coherence would always decohere in the temperatures found found in biological systems.

This paper by Collini et al describes X-ray crystallography studies of two types of marine cryptophyte algae that have long-lasting excitation oscillations and correlations and anti-correlations, symptomatic of quantum coherence even at ambient temperature. Distant molecules within the photosynthetic protein are thought to be connected to quantum coherence, and to produce efficient light-harvesting as a result. The cryptophytes can photosynthesise in low-light conditions suggesting a particularly efficient transfer of energy within protein. According to the traditional theory, this would imply only small separation between chromophores, whereas the actual separation is unusually large.

In this study, performed at room temperature, the antenna protein received a laser pulse, which results in a coherent superposition in the protein. The experimental data of the study shows that the superposition persists for 400 femtoseconds and over a distance of 2.5 nanometres. Quantum coherence occurs in a complex mix of quantum interference between electronic resonances, and decoherence caused by interaction with the environment. The authors think that long-lived quantum coherence facilitates efficient energy transfer across protein units. P. The authors remains uncertain, as to how quantum coherence can persist for hundreds of femtoseconds in biological matter. One suggestion is that the expected rate of decoherence is slowed by shared or correlated motions in the surrounding environment. Where light-harvesting chromophores are covalently bound to the protein backbone, it is suggested that this may strengthen correlated motions between the chromophores and the protein.

In the same issue of 'Nature' that published Collinis study, the 'News and Views' section of the journal also comments on her paper. It emphasises that this is the first study in which quantum coherence in photosynthetic proteins has been observed at room temperature. It comments on the remarkable efficiency of energy transfer, between the antennas that guide excitation energy from hundreds of light-absorbing pigment molecules towards the subsequent reaction centres that drive biochemical events. Collini is suggesting that quantum coherence could be a factor in this efficiency.

Earlier studies had observed coherent behaviour in green sulphur bacteria, but at very low temperatures. Collini et al observed quantum coherence in the antenna, and found that this persisted over 400 femtoseconds, in contrast to an expectation in traditional theory of only 100 femtoseconds. Coherence was observed between widely separated pigment molecules. This has also been observed in bacterial light-harvesting complexes. However, this was at very low temperatures, while the Collini study was at room temperature. Engel et al, who were responsible for some of the earlier studies, have speculated that quantum coherence allows antennas to search for the lowest energy state of the complex more efficiently, thus enhancing the energy transfer to the reaction centre. Coherence might help excitations to avoid local energy traps or minima, on their way to the reaction centre. Covalent binding to the protein backbone is speculated to make coherence longer lasting.

Perhaps the most surprising aspect of this latest paper on coherence in proteins is the speed with which news of the development has made its way to the level of more popular science, in the form of a useful full page summary by Kate McAlpine in the 'New Scientist'. She mentions that Gregory Engel, who was respnsible for the earlier low temperature studies of coherence in bacterial proteins, is enthusiastic about the Collini result. Engel and his group have also performed a study at 4 degrees centigrade, much above previous levels, although below the 21 degrees of the Collini study. Engel is also quoted as saying that this work could have implications for quantum computing, where a core problem has been to operate at the very low temperatures that are usually thought necessary to prevent quantum decoherence. The speed with which this work has been picked up and given prominence in a popular science magazine suggests a background change of attitude to coherence in protein. The vexed question of quantum consciousness is not mentioned, but the suggestion of activities within protein as a model for quantum computing is moving is in that direction.