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March 8, 1999 - March 21, 1999
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Researchers Tether the Velocity of Light
To 38 Miles Per Hour


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By Ryan Chuang
The Stanford Daily
Stanford University
Published Mar. 8, 1999


(U-WIRE) STANFORD, Calif. -- Light travels at 186,282 miles per second in a vacuum. But a physics team in Boston, including Prof. Steve E. Harris of Stanford's Applied Physics and Electrical Engineering Departments, has managed to slow down the speed of light to 38 miles per hour - reducing the speed of light by a factor of 20 million.

The group, headed by Lene Vestegaard Hau of the Rowland Institute for Science and Harvard University, eventually expects to slow the speed of light to the rate of a tortoise - 120 feet an hour.

Hau, two Harvard graduate students and Harris had their achievement reported in the Feb. 18 issue of Nature.

Scientists have known for years that they can slow down the speed of light slightly by shining it through a transparent medium such as glass, plastic or diamond. Indeed, for the last seven years, one of Harris' research groups has studied an optical effect called "electromagnetically induced transparency" in ordinary atoms.

Using this optical effect, the scientists make ordinarily opaque clouds of vapor transparent.

Four years ago, the Harris group was able to slow light to less than 120,000 miles per second by shining it through a cloud of illuminated lead atoms

Harris gave a lecture on the subject at Harvard a little more than a year ago, suggesting that the speed of light could be slowed even further.

"Lene was in the audience and was very interested, so we set up a collaboration," Harris said, explaining how the project began.

Hau proceeded to slow the speed of light by shooting a laser beam through a super-cooled glob of optical sodium molecules - called a Bose-Einstein condensate - that were only 50 billionths of a degree above absolute zero.

Dr. Hau's group reached this ultra-low temperature in stages, using lasers to slow the atoms in a confined gas and then evaporating away the warmest remaining atoms.

The temperature attained was one of the lowest ever reached in a laboratory and was far cooler than anything in nature, even in the depths of space.

The laser techniques for chilling atoms were first suggested by Stanford Nobel laureate Arthur Schawlow and actually done for the first time by a research team headed by Prof. Steve Chu in the Physics Department before Schawlow came to Stanford. Chu won the Nobel Prize in 1997 for this achievement.

Bose-Einstein condensates are named after the two physicists, Satyendra Nath Bose and Albert Einstein, who first predicted the existence of this new type of matter.

In a Bose-Einstein condensate, atoms are so cold they are forced to overlap with one another and merge into superatoms sharing the same properties.

Currently, the process of slowing light this way is too expensive to have any practical applications.

In the future, however, this research has the potential to help create ultrasensative night-vision goggles and improve computers and communication devices.

The research could also lead to techniques for making television displays and laser light shows more vivid.

Indeed, according to Harris, "If it cost a quarter to do, instead of $250,000, you would see it all over the place."

In early April, Hau will speak at the Applied Physics / Physics Colloquium at Stanford.

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