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Light Stands Still in Atom Clouds

Two independent teams of physicists have overcome the restless nature of light and stopped laser pulses in their tracks. A proposed method, now in tests by a third team, may even make light pulses creep backwards.

It's not normal for photons to stop, let alone to back up. Those quintessential particles of light usually zip straight through a vacuum at 300,000 kilometers per second and traverse other materials at slower but still dazzling speeds.

In a sense, stopping light is a trivial feat, comments Michael Fleischhauer of Kaiserslautern University in Germany, who helped develop the theory behind the new stopping techniques. "Take a black piece of paper and you can stop light very easily," he notes. However, the photons absorbed by that paper are destroyed.

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