 "BIRD brain" is usually an insult, but that may have to change. A light-activated compass at the back of some birds' eyes may preserve electrons in delicate quantum states for longer than the best artificial systems. Migrating birds navigate by sensing Earth's magnetic field, but the exact mechanisms at work are unclear. Pigeons are thought to rely on bits of magnetite in their beaks. Others, like the European robin (pictured), may rely on light-triggered chemical changes that depend on the bird's orientation relative to Earth's magnetic field. A process called the radical pair (RP) mechanism is believed to be behind the latter method. In this mechanism, light excites two electrons on one molecule and shunts one of them onto a second molecule. Although the two electrons are separated, their spins are linked through quantum entanglement. The electrons eventually relax, destroying this quantum state. Before this happens, however, Earth's magnetic field can alter the relative alignment of the electrons' spins, which in turn alters the chemical properties of the molecules involved. A bird could then use the concentrations of chemicals at different points on its eye to deduce its orientation. |
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