Quantum Evidence 6

1.) Entanglement and the entangling power of the dynamics in light harvesting complexes - Caruso, F. et al - Discusses quantum coherent and incoherent processes within photosynthetic protein.

2.) Distribution of entanglement in light harvesting complexes and their quantum efficiency - Francesca Fassioli & Alexandra Olaya-Castro - Discusses efficacy of quantum coherence and entanglement in responding to the environment.

3.) Towards quantum superposition of living organisms - Romero-Isart, O. et al

4.) Quantum entanglement in photosynthetic light harvesting complexes - K. Birgitta Whaley et al - Discusses quantum entanglement in photosynthetic organisms

1.)

Entanglement and the entangling power of the dynamics in light harvesting complexes

Caruso, F. et al, Imperial College

arXiv:0912.0122v1 [quant-ph] (2010)

This paper studies the evolution of quantum entanglement during exciton energy transfer (EET) in the Fenna-Matthews-Olson (FMO) complex in sulphur bacteria. In these bacteria energy from sunlight has to be transferred from antennae that collect it to the reaction centre which changes it into chemical energy. The efficiency of this energy transfer through light harvesting complexes, such as the FMO or a similar structure in other organisms known as the LH-1, is surprisingly high at 99%. In recent studies, such as Engel (2007), evidence of quantum coherence has been found in these structures, and it has been suggested that this could have a role in the high efficiency of energy transfer. Surprisingly the tendency for quantum states to decohere in the environment and the random noise of the environment is thought to play a positive role in energy transport. P. Light harvesting complexes such as the FMO consist of several chromophore molecules coupled to one another by dipolar interactions, and situated within a protein scaffold. Sun light induced excitations on individual chromophores can undergo quantum coherent transfer from site to site and are thus delocalised as a wave form over multiple chromophore molecules. Quantum coherence is a necessary but not sufficient condition for the existence of quantum entanglement.

Efficient exciton energy transfer in light harvesting complexes is traced to the interplay between quantum coherent and incoherent processes, with the quantum correlations that are characteristic of coherence partially suppressed by noise, but not completely destroyed. The interplay between entanglement over short distances and times followed by the destruction of entanglement over longer distances and times is seen as necessary for optimal energy transport.

From the point of view of consciousness studies, there is an interesting contrast between the mixed coherent/incoherent systems discussed here, which appear to be functional in photosynthetic protein, and the insistence that any decoherence in the brain is a sudden death as far as the efficacy of quantum states is concerned. We may have to await further clarification of this.

2.)

Distribution of entanglement in light harvesting complexes and their quantum efficiency

Francesca Fassioli & Alexandra Olaya-Castro, Oxford University, University College London

arXiv:1003.3610v1 [quant-ph]

This paper suggests that electronic quantum coherence amongst distance donors could allow precise modulation of the light harvesting function. Photosynthesis is remarkable for the near 100% efficiency of energy transfer. The spatial arrangement of the pigment molecules and their electronic interaction is known to relate to this efficiency.

Recent experimental studies of photosynthetic protein have shown that it can sustain quantum coherence for longer than previously expected, and that this can happen at the normal temperature of biological processes. This has been taken to imply that quantum coherence may affect light harvesting processes. In photosynthesis, the energy of sunlight is transferred to a reaction centre with near 100% efficiency. The spatial arrangement of pigment molecules and their electronic interactions is known to be involved with this high efficiency. There is an implication that quantum coherence may affect the light harvesting process.

Some studies point to very efficient energy transport as the optimal result of the interplay of quantum coherent with decoherent mechanisms. Roles proposed for quantum coherence vary between avoidance of energy traps that are not at the overall lowest energy level, and actual searches for the overall lowest energy level. In this paper, it is suggested that the function of quantum coherence goes beyond efficiency of energy transport, and includes the modulation of the photosynthetic antennae complexes to deal with variations in the environment.

Role of quantum entanglement: There is some debate as to whether quantum entanglement plays a role in the functioning of the light-harvesting complexes, or is just a by-product of quantum states. The authors argue that entanglement may be involved in the efficiency of the system, and they use the FMO protein in green sulphur bacteria as the basis of their study. They suggest that entanglement could play a role in light-harvesting by allowing precise control of the rate at which excitations are transferred to the reaction centre. Interplay between quantum coherent and incoherent processes is also noticed, with one state being more or less efficient than the other depend on the type of coupling to the environment.

Long-lived quantum coherence: Long-range quantum correlations have been suggested to be important as a mechanism helping quantum coherence to survive at the high temperatures sustained in light harvesting antennae. Electronic coherence is distributed amongst pigment molecules, and it is suggested that it may adjust energy transport properties in relation to light intensity. This paper claims to show that in the FMO complex long-lived quantum coherence is spatially distributed in such a way that entanglement between pairs of molecules controls the efficiency profile needed to cope with variations in the environment. The ability to control energy transport under varying environmental conditions is seen as crucial for the robustness of photosynthetic systems. A mechanism involving quantum coherence and entanglement might be effective in controlling the response to different light intensities.

Consciousness: From the point of view of consciousness studies, the discussion in this paper might suggest greater caution in proposing simplistic dismissals of the possible influence of quantum coherence in neural tissues. This paper indicates the possibility that quantum entanglement helps to sustain coherence at biological temperatures, and also that fluctuations between coherent and decoherent mechanisms may be important within the same system.

3.)

Towards quantum superposition of living organisms

Romero-Isart, O. et al, Max Planck Institute, ICFO & ICREA

New Journal of Physics, 12, (2010) 033015 (16pp) doi:10.1088/1367-2630/12/3/033015

Recent research has shown that it is possible to create superpositions of collections of photons. This has given rise to speculation as to what the size limit to such collections might be, and whether it might even be possible to put a small organism such as a virus into superposition. Technical progress suggests that it will be possible to increase the size of the collections put into superposition. Pieces of technology such as micro-mirrors or cantilevers may be put into superposition, as could micro-organisms such as viruses. Experiments depend on an optical cavity with a mechanical oscillator, where the experimenter attempts to reduce the mechanical object to its ground state. Achievement of this is expected to open up the possibility of more fundamental and applied experiments, including those with micro-organisms.

The authors consider experiments on micro-organisms to be feasible because they behave as dielectric objects, which have been used in other forms of these experiments, some micro-organisms are resistant to the vacuum conditions of these experiments, and the sizes of some organisms such as spores and viruses is comparable to the wavelengths involved in these experiments. The authors anticipate that such experiments could address the role of life and consciousness in quantum mechanics.

Conclusion: It is not immediately easy to see where this work is leading in terms of the understanding of consciousness. Most theories of quantum consciousness look at the possibility of consciousness deriving from quantum states within complex organisms, whereas here we have the potential for whole organisms to be put into superposition. There may be some connection to the idea that the surprising capabilities of micro-organisms depend on quantum computing, but even here the mechanisms proposed are seen as a detailed part of the internal structure.

4.)

Quantum entanglement phenomena in photosynthetic light harvesting complexes

K. Birgitta Whaley, Mohan Sarovar & Akihito Ishizaki, University of California Berkeley

arXiv: 1012.4059vl [quant-ph] 18 December 2010

This paper discusses recent studies of photosynthetic light harvesting complexes. The studies are seen as having established the existence of quantum entanglement in biologically functional systems that are not in thermal equilibrium. However, this does not necessarily mean that entanglement has a biological function. The authors point out that the modern discussion of entanglement has moved from simple arrangements of particles to entanglement in larger scale systems.

Measurements of excitonic energy transport in photosynthetic light harvesting complexes show evidence of quantum coherence in these systems. A particular focus of research has been the Fenna-Matthew-Olson (FMO) complex in green sulphur bacteria. The FMO serves to transport electronic energy from the light harvesting antenna to the photosynthetic reaction centre. Coherence is present here at up to 300K. In 2009, quantum coherence was also detected in the light harvesting antenna of green plants (1. Calhoun et al). Studies have also demonstrated quantum coherence within the photosynthetic reaction centre. There is thus now a growing body of evidence for quantum coherence in connection with energy transports in plants and bacteria.

The electronic excitations in the chromophores are coupled to the vibrational modes of the surrounding protein scaffolding. One study (2. Scholak et al, 2010) shows a correlation between the extent of entanglement and the efficiency of energy transport. That study went on to claim that efficient transport requires entanglement, although the authors of the present paper query such a definite assertion.

The FMO complex is described as acting as a 'quantum wire' to transmit electronic excitation from the light harvesting antenna to the reaction centre. The authors draw attention to the relationship between electronic excitations in the chromophores and those in the surrounding protein. A previous study by one of the authors (3. Sarovar et al, 2010) shows that for structures such as the FMO coherence and entanglement are necessary and sufficient for one another.

The pigment-protein dynamics generates entanglement across the entire FMO complex in only 100 femtoseconds, but followed by oscillations that damp out over several hundred femtoseconds with a subsequent longer contribution continuing beyond that for up to about five picoseconds. This more persistent entanglement can be at between a third and a half of the initial value and 15% of the maximum possible value. Long-lived entanglement takes place between four or five of the existing seven chromophores. The most extended entanglement is between chromophores one and three, and these are also two of the most widely separated chromophores. Studies also show that this entanglement is quite resistant to temperature increase, with only a 25% reduction when the temperature rises from 77K to 300K. Overall studies indicate long-lived entanglement of as much as five picoseconds between numbers of excitations on spatially separated pigment molecules. This is described here as long-lived coherence because energy transfer through the FMO complex is on a time span of a few picoseconds meaning that the up to five picoseconds of entanglement seen between the chromophores represents a functional timescale. However, the authors do not consider this by itself to be a conclusive argument for entanglement being functional in the FMO.

This paper also looks at light harvesting complex II (LHCII), which is also shown to have long-lived electronic coherence. LHCII is the most common light harvesting complex in plants. The system comprises three subunits each of which contains eight chlorophyll 'a' molecules and six chlorophyll 'b' molecules. A study by two of the authors (4. Ishizaki & Fleming, 2010) indicates that only one out of chlorophyll molecules would be initially excited by photons, and this molecule would then become entangled with other chlorophyll molecules. Entanglement decreases at first, but then persists at a significant proportion of the maximum possible value. This is also an important feature of the FMO complex. In both these complexes entanglement is seen to be generated by the passage of electronic excitation through the light harvesting complexes, and to be distributed over a number of chromophores. Entanglement persists over a longer time and is more resistant to temperature increase than might have been previously expected. A functional biological role is suggested by the persistence of entanglement over the same timescale as the energy transfer within the light harvesting complexes.

References:-
1.) Calhoun, T.R. et al (2009) - Journal of Physical Chemistry B, 113, 16291
2.) Scholak, T. et al (2010) - arXiv:0912.3560v2 [quant-ph]
3.) Sarovar, M. et al (2010) - Natural Physics, 6, 462
4.) Ishizaki, A. et al (2010) - Phys. Chem. Chem. Phys. 12, 7319