It’s difficult to prove that a device said to be a quantum computer actually is one. While entanglement is a requirement for the quantum performance of machines like D-Wave, it is not a proof. But the remarkable abilities of birds to navigate using Earth’s minute magnetic field are now similarly believed to depend on a biological quantum compass — although proving it is another story.

At a meeting of the American Physical Society this Wednesday in Texas, Peter Hore will be describing new experimental results that help explain how avian magnetoreception might actually work. Like many other organisms, birds have many special adaptions to help them navigate. In addition to the ability to detect things like polarized light, they have any number of ways they might use to sense magnetic fields. The idea that they use magnetic particles within the neurites coursing through their beaks, while conceivable, is no longer the best explanation for their abilities.

Closer inspection now suggests that those particles are just incidental iron concretions packaged in macrophages with no direct link to their nervous systems. A better way to try to do it, a way birds appear to have found, may be to use a chemical compass instead. The main idea is that light-activated chemical reactions occurring within the bird’s eyes are sensitive not just to the strength of a magnetic field, but to its direction.

In order to work, there needs to be a way to preserve and amplify small magnetic effects that are ‘hidden’ beneath a much larger thermal background to the point of detection. One mechanism up to the job is to use something known as radical pairs. Radical pairs are two simultaneously created molecules, with each possessing a single unpaired electron whose spin is correlated to that of the other.

A light-sensitive protein known as cryptochrome is found in the oriented cells of the retina of many animals and seems to fit the bill. At its core is a cofactor known as FAD that is constrained by several of the protein’s tryptophan amino acids. When activated by blue or green light, electron transfer within the cryptochrome complex gives rise to just the kind of radical pair that is needed for a magnetic field sensor.

Together with Henrik Mouritsen, Peter Hore has been testing the sensitivity of this magnetic field sensor in Eurasian Robins. Their experiments basically look at the ability of the robins to orient themselves when the strength of the background magnetic field, or that of disruptive electromagnetic interference, is varied. Other researchers have reported that swapping out the seemingly crucial tryptophans residues in the various cryptochromes of other animals like flies had no effect. So I asked Peter what those findings imply for birds. He notes that any one of their four cryptochromes could potentially be the primary magnetoreceptor, in vivo or in vitro, and that there could also be alternatives to FAD-tryptophan electron transfer.

In quantum computers, superposition and entanglement quickly decay without using high vacuum and cryogenic temperatures. If life has evolved mechanisms using room-temperature radical pairs in proteins to do the similar kinds of things that researchers now need hundreds of pounds of equipment to do, then we clearly have something we can learn from it.

Researchers have already been able to construct a radical-pair based chemical from scratch to study quantum coherence effects. For one such molecule they used a fullerene linked to two molecules that are important to many processes in cells, namely porphyrins and carotenoids.

While other kinds of reactions occurring in vision and photosynthesis may make use of quantum phenomena in their initial excitation, the latest research suggests that only magnetoreception may require extended maintenance of quantum coherence. Using these kinds of newly discovered abilities of animals to guide our efforts to make truly quantum computers may be just the beginning. Many other kinds of sensors and detectors might be imagined — perhaps even ways to improve common instruments like radar, or NMR devices to peer into our brains.