But exactly how plants manage this nearly instantaneous trick has remained elusive. Now biophysicists at the University of California, Berkeley, have shown that plants use the basic principle of quantum computing—the exploration of a multiplicity of different answers at the same time—to achieve near-perfect efficiency. Biophysicist Gregory Engel and his colleagues cooled a green sulfur bacterium—Chlorobium tepidum, one of the oldest photosynthesizers on the planet—to 77 kelvins [— degrees Fahrenheit] and then pulsed it with extremely short bursts of laser light.
But quantum effects are typically limited to the very small, and only really observable in perfect, laboratory conditions. A living being, with its wet, messy systems, would be a tough place to find some quantum weirdness lurking — and yet we have.
Above is the photosynthetic complex of light-harvesting green sulfur bacteria. The green and yellow circles highlight the two molecules simultaneously excited. Credit: Dr. Einstein received his Nobel Prize for showing, in , that quantizing light into photons led to better explanation of how light interacts with matter. Feynman received his Nobel prize for working out, in the s, how light interacts with charged subatomic particles such as electrons.
Thompson discovered the electron in , for which he received a Nobel Prize. If they were moving in that way, they would continuously radiate energy, and such radiation had not been observed. This problem was not resolved until Bohr constructed his quantized model of the atom in , for which he also received a Nobel Prize. This idea leads to expectations, and when turned into math, to predictions that are completely wrong.
It is better to just think of energy moving around the molecule, energy that changes the way that the electrons in the molecule are arranged. The main problem with thinking about electrons as little billiard balls is that one then tends to think of the electrons as moving along particular paths through space.
In the context of electron transport in photosynthesis, one thinks of an electron as moving from one part of the molecule to another part, and then to another part, etc.
This is a very classical-physics picture, and it is wrong. As first shown experimentally by Engel et al. The results of Engel et al. Engel et al. Much more detailed - and much more difficult - calculations that treat more of the molecular structure using quantum theory correctly reproduce the results of Engel et al. The third step in photosynthesis is a set of coupled chemical reactions.
Chemical reactions involve energetically re-arranging electrons so extensively that large molecules dissociate into smaller molecules or small molecules associate to form larger molecules. Understanding how electrons fit into even the simplest atoms - the Bohr model was developed for the simplest atom, Hydrogen - requires quantum theory.
After the binding of the chemical to the receptor, the chemical would then act as a bridge allowing for the electron to be transferred through the protein. Even though there are such large separations between redox sites within enzymes, electrons successfully transfer in a generally temperature independent aside from extreme conditions and distance dependent manner.
To empirically suggest the involvement of entanglement, an experiment would need to be devised that could disturb entangled radical-pairs without disturbing other radical-pairs, or vice versa, which would first need to be demonstrated in a laboratory setting before being applied to in vivo radical-pairs. But qubits are typically cooled to within a fraction of a degree of absolute zero, and even then, coherence survives only for brief instants, among just a handful of bits, before decoherence sets in due to disturbance from the surrounding environment. We found that the properties of some of the chromophore vibrations that assist energy transfer during photosynthesis can never be described with classical laws, and moreover, this non-classical behaviour enhances the efficiency of the energy transfer. In plants, photosynthesis occurs in the chloroplasts of the plant cells.
Reaction centre: A molecular model of the Fenna—Matthews—Olson pigment—protein complex, as found in the green sulphur bacterium Prosthecochloris aestuarii. The complete failure of classical physics to explain how light reacts with matter is why we have quantum theory in the first place.
Chlorophyll within the chloroplasts is used to synthesise glucose from water H2O and carbon dioxide CO2 using the energy from sunlight, with oxygen O2 released as a by-product. We would never have the concepts coming out of current genome biology or neuroscience, for example, if no one had invented DNA sequencers or fMRI machines, or if we were still trying to do our computing on s workstations.