Greased lightning

By Justin Mullins So much for the ultimate speed limit. Scientists in Switzerland have measured how fast information can flow in the quantum world and have clocked it travelling 1500 times faster than light. The Swiss speed trap involved pairs of “entangled” photons. Once linked, the pair behave as one, even if the photons are on opposite sides of the Universe. Physicists don’t think this flouts the light-speed limit enshrined in relativity. “You cannot use this effect to communicate, it’s not like ordinary information,” says Wolfgang Tittel of the University of Geneva. But the Swiss team wondered just how fast such communication could travel. So they created an entangled pair in their Geneva lab and sent the two photons in opposite directions along a 10.6-kilometre optical fibre. Because the two arms of the fibre are not exactly the same length, one photon will arrive first and will change its state when detected. This will change the state of the other which will be detected shortly after. Hence the researchers know they communicated in the short time between the first and second detection and can calculate the minimum speed of that communication. That speed was at least 4.5 e 1011 metres per second, enough to reach the nearest star, Alpha Centauri, in just over a day. Ordinary light would take 4.3 years. Source: Quantum Physics e-print 0007008 at http:
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