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Thursday, July 25, 2013

STOP that light

Crédito: Adrian
Credit: Adrian
The fastest thing in the universe was completely stopped and stored for a minute (new record). In vacuum, light travels about 18 million kilometers, in those 60 seconds - which represents more than 20 trips to the moon and back.
"A minute is a very, very long," says Thomas Krauss, St. Andrews University, UK. "This is really an important milestone."
The exploit could allow secure quantum communications to work at long distances.
As the light typically travels just under 300,000 kilometers per second in a vacuum, physicists  were able to slow it down just to only 17 meters per second in 1999, and two years later, stop it completely, though only by a fraction of a second. Earlier this year, researchers increased this time stopping the light for 16 seconds using cold atoms.
Light Trap
To break the minute barrier, George Heinze and colleagues at the University of Darmstadt, Germany, fired a laser control over an opaque crystal, the atoms leading to a quantum superposition of two states. This made it clear to a small range of frequencies. The Heinze's team then stopped a second laser beam which entered the crystal, turning the first laser off and, consequently, the transparency of that crystal disappeared.
The storage time depends upon the crystal's superposition. A magnetic field extends it, but it complicates the configuration of the control laser. Heinze's team used an algorithm to "generate" the magnets and laser combinations, leading them to trap the light for a minute.
Should still be possible to achieve longer storage of light with other crystals, Heinze says, as they did with the physical limits of this material.
Fonte: newscientist

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