First Evidence of Entanglement in Photosynthesis

Physicists are fascinated with entanglement, the strange quantum phenomenon in which distinct objects share the same existence, regardless of the distance between them. But in their quest to study and exploit entanglement for information processing, physicists have found it fragile and easily destroyed. This fragility seems to severely limits how entanglement might ever be used.

But a new, more robust face of entanglement is beginning to emerge from other types of experiment. For example, physicists have recently found the signature of entanglement in the thermal states of bulk materials at low temperatures. This has huge implications for biological systems: if entanglement is more robust than we thought, what role might it play in living things?

Now we’re beginning to find out. In the first rigorous quantification of entanglement in a biological system, an answer is beginning to emerge. Researchers from various institutions in Berkeley California have shown that molecules taking part in photosynthesis can remain entangled even at ordinary atmospheric temperatures.

The evidence comes from detailed study of light sensitive molecules called chromophore that harvest light in photosynthesis.

Various studies have shown that in light harvesting complexes, chromophores can share coherently delocalised electronic states. K. Birgitta Whaley at the Berkeley Center for Quantum Information and Computation and pals say this can only happen if the chromophores are entangled.

They point out that these molecules do not seem to exploit entanglement. Instead, its presence is just a consequence of the electronic coherence.

This is a big claim that relies somewhat on circumstantial evidence. It’ll be important to get confirmation of these idea before they can become mainstream.

Nevertheless, if correct, the discovery has huge implications. For a start, biologists could tap into this entanglement to make much more accurate measurement of what goes on inside molecules during photosynthesis using to the various techniques of quantum metrology that physicists have developed.

More exciting still, is the possibility that these molecules could be used for quantum information processing at room temperature. Imagine photosynthetic quantum computers!

And beyond that is the question that Whaley and co avoid altogether. If entanglement plays a role in photosynthesis, then why not in other important biological organs too? Anybody think of an organ where entanglement might be useful?

Ref: arxiv.org/abs/0905.3787: Quantum Entanglement in Photosynthetic Light Harvesting Complexes