| Light "Stopped in its tracks"
I just re-noticed this press release I received a couple of days ago from NASA. As the speed of light has been a topic here a few times, I thought that some of you might find this interesting. I will try to comment on this later.
[quote]
FROZEN LIGHT: COOL NASA RESEARCH HOLDS PROMISE
NASA-funded research at Harvard University, Cambridge,
Mass., that literally stops light in its tracks, may someday
lead to breakneck-speed computers that shelter enormous
amounts of data from hackers.
The research, conducted by a team led by Dr. Lene Hau, a
Harvard physics professor, is one of 12 research projects
featured in a special edition of Scientific American
entitled "The Edge of Physics," available through May 31.
In their laboratory, Hau and her colleagues have been able
to slow a pulse of light, and even stop it, for several-
thousandths of a second. They've also created a roadblock
for light, where they can shorten a light pulse by factors
of a billion.
"This could open up a whole new way to use light, doing
things we could only imagine before," Hau said. "Until now,
many technologies have been limited by the speed at which
light travels."
The speed of light is approximately 186,000 miles per second
(670 million miles per hour). Some substances, like water
and diamonds, can slow light to a limited extent. More
drastic techniques are needed to dramatically reduce the
speed of light. Hau's team accomplished "light magic" by
laser-cooling a cigar-shaped cloud of sodium atoms to one-
billionth of a degree above absolute zero, the point where
scientists believe no further cooling can occur. Using a
powerful electromagnet, the researchers suspended the cloud
in an ultra-high vacuum chamber, until it formed a frigid,
swamp-like goop of atoms.
When they shot a light pulse into the cloud, it bogged down,
slowed dramatically, eventually stopped, and turned off. The
scientists later revived the light pulse and restored its
normal speed by shooting an additional laser beam into the
cloud.
Hau's cold-atom research began in the mid-1990s, when she
put ultra-cold atoms in such cramped quarters they formed a
type of matter called a Bose-Einstein condensate. In this
state, atoms behave oddly, and traditional laws of physics
do not apply. Instead of bouncing off each other like bumper
cars, the atoms join together and function as one entity.
The first slow-light breakthrough for Hau and her colleagues
came in March 1998. Later that summer, they successfully
slowed a light beam to 38 miles per hour, the speed of
suburban traffic. That's two million times slower than the
speed of light in free space. By tinkering with the system,
Hau and her team made light stop completely in the summer of
2000.
These breakthroughs may eventually be used in advanced
optical-communication applications. "Light can carry
enormous amounts of information through changes in its
frequency, phase, intensity or other properties," Hau said.
When the light pulse stops, its information is suspended and
stored, just as information is stored in the memory of a
computer. Light-carrying quantum bits could carry
significantly more information than current computer bits.
Quantum computers could also be more secure by encrypting
information in elaborate codes that could be broken only by
using a laser and complex decoding formulas.
Hau's team is also using slow light as a completely new
probe of the very odd properties of Bose-Einstein
condensates. For example, with the light roadblock the team
created, they can study waves and dramatic rotating-vortex
patterns in the condensates.
The Harvard research team includes Hau; Drs. Zachary Dutton,
Chien Lieu, Brian Busch and Michael Bu
__________________
Noah Moses
"And, when he shall die, take him and cut him out in little stars, and he will make the face of heaven so fine that all the world will be in love with night, and pay no worship to the garish sun."--William Shakespeare | 
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