Do birds see with quantum eyes?

Quantum Biology in action!

A quantum trick might be behind birds’ ability to navigate using Earth’s magnetic field lines.


Some researchers think birds might be able to “see” the magnetic field via photosensitive proteins in their retinas. The theory is that when a photon strikes one of these proteins, it creates a pair of oppositely charged ions, which separate for a fleeting moment before recombining. Each of these ions contains electrons with a quantum property called spin. Initially, these spins point in opposite directions – but in a magnetic field, they tend to become aligned. When the ions recombine, this alignment triggers a specific biochemical reaction, which gives the bird information about the magnetic field.


The idea has a major flaw though. The ions seem to be pulled back together about 10 times faster than researchers think Earth’s magnetic field could affect the electrons’ spins.


Now Iannis Kominis of the University of Crete in Heraklion, Greece, suggests that a known quantum effect might be able to ramp up the impact of the magnetic field in enough time. “Quantum physics comes to the rescue,” he says.


The “quantum Zeno” effect occurs when repeated measurements of a quantum system are made. While these measurements are taking place particles do not change their state, as if they know they’re being watched.


Kominis’s calculations show that the force pulling the two ions together might also induce the Zeno effect on the electrons. It would allow the magnetic field to align the spins while the ions are separated by momentarily overcoming the disturbing influences of noise in the biochemical environment, thereby amplifying the magnetic field’s influence (


Kominis and his colleagues have already shown that the Zeno effect can increase the sensitivity of a quantum system to a magnetic field. They did this by filling a chamber with a dense gas, thereby building a highly sensitive atomic magnetometer – a device used to detect magnetic fields.


They then applied a magnetic field so weak that many magnetometers would be unable to detect it. But because the gas was so dense, the group showed that the atoms effectively measure each other when they collide and, overall, that keeps the spin of the particles locked in the same state. This made the device strong enough to detect the magnetic field.


Other researchers doubt whether such quantum processes are at play in birds’ eyes, however. “I’m a fan of daring hypotheses, but I’m not sure what this theory explains,” says biologist Sonke Johnsen of Duke University in Durham, North Carolina.


He also points out that the ion reaction theory has bigger problems than the lack of time for the magnetic field to have an effect. “It’s not at all clear how to make a directional sensor out of molecules that are freely diffusing and rotating,” he says. In other words, the bird might be able detect the field, but not what its orientation is.


Physicist Thorsten Ritz at the University of California, Irvine, says the idea may have merit, however. “It’s really cute and worth exploring further,” he says, “but I’d want to see experimental tests before I believe it.”











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