Using two villages on opposite sides of Geneva as their lab, Swiss physicists have taken one of the strangest phenomena of quantum mechanics to a new level. From Geneva they sent a pair of photons along fiber-optic cables [pdf], one to each village. When they measured one photon upon its arrival, the other changed instantaneously —though it was 11 miles away. This weird linkage, called quantum entanglement, raises exotic possibilities like teleportation. When two particles are entangled, the measurement of one immediately affects the other, no matter how distant. It’s so counterintuitive that Albert Einstein dismissed it as “spooky action at a distance.” Such entanglement had been observed before, but never over such a great distance.
One might assume that one particle sent an ultrafast signal to its partner, says physicist Nicolas Gisin, a member of the University of Geneva team. If that were true, the quantum communiqué would have traveled at more than 10,000 times the speed of light, something difficult to reconcile with the known laws of physics. “Nature does not function that way,” Gisin says. In relativity theory, communicating faster than light speed is not possible. But the correlations observed in entangled photons cannot be used to communicate any kind of signal, so they do not violate the theory. Still, Gisin says, “We have to admit this is a really big conceptual change.”