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Physicists stop and start light
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PHYSICISTS say they have brought light particles to a screeching halt, then revved them up again so that they could continue their journey at a blistering 186,000 miles per second.
The results are the latest in a growing number of experiments that manipulate light, the fastest and most ephemeral form of energy in the universe.
Eventually, researchers hope to harness its speedy properties in the development of more powerful computers and other technologies that store information in light particles rather than electrons.
To stop light completely, researchers created a trap in which atoms of gas were chilled magnetically to within a few-millionths of a degree of absolute zero and a consistency they described as ``optical molasses''. One experiment group used sodium atoms, while another used rubidium, an alkaline metal.
Normally, the gas atoms would absorb any light directed into the trap. The researchers solved this problem by aiming a ``control'' laser beam into the gas, which transformed it from opaque to a state known as electromagnetic ally induced transparency, or EIT.
Then they shined a second, probe laser that operated at a different frequency. When the wave of light particles hit the gas atoms, the particles slowed dramatically.
To stop the probe light entirely, the researchers waited until it had entered the vessel, encountered the gas atoms and imprinted a pattern into the orientation of the spinning atoms.
Then the scientists gradually reduced the intensity of the control beam.
As a result, the probe light dimmed and then vanished. But information in the light particles still was imprinted on the atoms of sodium and rubidium, effectively freezing or storing it, according to scientists.
Then the scientists gradually restored the control beam. The light that had been stored in the spinning atoms was reconstituted and continued its journey through the vessel.
``It's as if you stretched a silk thread across a railroad track and a train vanishes into it,'' said University of Colorado physicist Eric Cornell, who reviewed the study for Nature.
``You wait and then - bam! - The train reappears and goes zooming down the track,'' Cornell said. ``It's not at all what you would expect from a pulse of light.''
About 50 per cent of the light - and its information - was retrieved in the regenerated light pulse, scientists said. That might not be good enough for a practical computing system, but it demonstrates how such a system might store and ship data.(SD-Agencies)
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