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Scientists freeze pulse of light, for an instant

/ Source: The Associated Press

Physicists say they have brought light to a complete halt for a fraction of a second and then sent it on its way, an achievement that could someday help scientists develop powerful new computers.

The research differs from work published in 2001 that was hailed at the time as having brought light to standstill.

In that work, light pulses were technically "stored" briefly when individual particles of light, or photons, were taken up by atoms in a gas.

Harvard University researchers have now topped that feat by truly holding light and its energy in its tracks _ if only for a few hundred-thousandths of a second.

"We have succeeded in holding a light pulse still without taking all the energy away from it," said Mikhail D. Lucian, a Harvard physicist.

Harnessing light particles to store and process data could aid the still distant goal of so-called quantum computers, as well as methods for communicating information over long distances without risk of eavesdropping.

The research may also have applications for improving conventional fiber-optic communications and data processing techniques that use light as an information carrier. Lukin said the present research is just another step toward efforts to control light, but said additional work is needed to determine if it can aid these applications.

The findings appear in Thursday's issue of the journal Nature.

Stanford University physicist Stephen Harris said the new research is promising and represents an important scientific first.

He said research published in 2001 by two teams _ including one that Lukin was part of _ stopped light in atoms of a gas much like a photograph stores an image.

Harris said the new work takes that another step by demonstrating for the first time that a light pulse can be stopped in "light form," rather than in the previous "photograph" form. "The light is honestly stopped," said Harris.

In the new work, Lukin and his colleagues sent light into a container filled with a gaseous form of rubidium, a metallic element. Lasers interacting with the gas first stored the light pulse in the rubidium atoms, just as in the earlier work.

But this time, Lukin's team next used a pair of lasers to simultaneously free the light's energy and cause the rubidium atoms to act as tiny, stacked mirrors. Those atomic mirrors held the light particles still until one laser was switched off and the light then escaped.

Matthew Bigelow, a scientist at the University of Rochester involved in light research, called the new study "very clever" and something that may ultimately spur the development of superior light-based computers.

"I think it's moving us in the right direction," he said.