Others think nature is leading us up the garden path. Is photosynthesis, for example, really made more efficient by exploiting quantum interference and superposition effects? "I think the jury is still out on this question," says Robert Blankenship of Washington University in St Louis, Missouri. "I think it is possible that, depending on the details of the system, it could just as easily decrease the efficiency." Simon Benjamin, a colleague of Vedral's at the University of Oxford, wonders how we can really put long-lived quantum states to work if indeed they do pop up in natural systems. "It's certainly too early to be making dramatic claims," he says.
All those stepping gingerly around this new field agree that caution is needed - yet there is a palpable sense of excitement. Max Planck first discovered quantum theory more than a century ago because of odd observations that could be explained in no other way. That led to the laser and the semiconductor and all the technological revolutions they have seeded. Quantum biology is at that early stage of inexplicable observations. Turin for one believes something big is emerging. "I can't help thinking we are seeing just a small part of a far, far bigger iceberg," he says.
When this article was first posted, it incorrectly stated that vanillin and isovanillin were forms of benzaldehyde.
Bird's eye view
Another instance of quantum effects in biology might be in how birds sense Earth's magnetic field (New Scientist, 27 November 2010, p 42). In 2004, Thorsten Ritz of the University of California, Irvine, showed how magnetic disturbances that would only show up on systems that could detect transitions between particular quantum-mechanical atomic spin states could disrupt the compass of the European robin, Erithacus rubecula.
Ritz suggested that birds come equipped with a sensor system containing spin states that flip in response to changes in Earth's magnetic field, producing signals that the bird's brain in some way detects. But how?
The first proposal was that some apparatus in the eye initiates a chemical response. But this would require a constant, fast flipping of spins to keep chemical information flowing, whereas the birds seemed to maintain delicate spin states for extraordinarily long times of up to 100 microseconds.
According to the late Marshall Stoneham of University College London and his colleagues, the problem might be overcome if the birds used something similar to a human visual peculiarity that detects light polarisation. Known as Haidinger's brush, this superimposes a faint, yellow bow-tie shape on our visual field, and is thought to result from the way blue light-absorbing lutein molecules are arranged in concentric circles within our eye. Stare at a blank piece of paper and a polarising filter or a blank document on a laptop screen and you can see it for yourself.
Stoneham calculated that a magnetic field could produce a similar distortion in a bird's visual field, the orientation of which would change with a change in magnetic field. Crucially, that would occur only if quantum states lasted long enough to affect many of the bird's light sensing molecules at the same time. Birds might see the result, Stoneham suggested, in a kind of a head-up display of the kind that is embedded in the windscreens of some luxury cars (arxiv.org/abs/1003.2628).
Michael Brooks is a consultant for New Scientist. His latest book is Free Radicals: The secret anarchy of science (Profile, 2011)
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