CNET News.com: Wizardry at Harvard: Physicists move light

[David Farber <dave () farber net>]

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Begin forwarded message:

From: bob () bobrosenberg com
Date: February 8, 2007 2:53:38 PM EST
To: dave () farber net
Subject: CNET News.com: Wizardry at Harvard: Physicists move light

Dave

Perhaps for IP.

If the article below is accurate, I suspect [after reading "GOP revives
ISP-tracking legislation" http://news.com.com/2100-1028_3-6156948.html],
that some in Congress will want to outlaw the technology.

How could they track quantum cryptography?  After all, when quantum
cryptography is outlawed, only outlaws will use quantum cryptography.
- --  

Cordially,

Bob Rosenberg, Principal
R.G. Rosenberg & Assoc.
Public Policy Consulting & Advocacy and
eACE - eLearning Advocacy Civic Entrepreneur
P.O. Box 33023
Phoenix, AZ  85067-3023
LandLine:  (602)274-3012
Mobile:  (602)206-2856
bob () bobrosenberg com
www.bobrosenberg.com

**********************************************

“Education's purpose is to replace an empty mind with an open one.”

       -- Malcolm Forbes

**********************************************

CNET News.com    http://www.news.com/
Wizardry at Harvard: Physicists move light

By Kenneth Chang
http://news.com.com/Wizardry+at+Harvard+Physicists+move+light/ 
2100-11395_3-6157563.html

Story last modified Thu Feb 08 11:10:27 PST 2007


It's like three-card monte. Now you see it. Now you don't. Then you see
it--over there.

In a quantum mechanical sleight of hand, Harvard physicists have shown
that they can not only bring a pulse of light, the fleetest of nature's
particles, to a complete halt, but also resuscitate the light at a
different location and let it continue on its way.

That ability to catch, store, move and release light could be used in
future computers to process information encoded in the light pulses.

"It's been a wonderful problem to try to wrap your brain around," said
Lene Vestergaard Hau, a professor of physics at Harvard and senior  
author
of a paper describing the experiment appearing Thursday in the journal
Nature. "There are so many doors that open up."

In 1999, Hau headed a team of scientists that slowed light, which  
travels
a brisk 186,282 miles a second when unimpeded, to a leisurely 38  
miles an
hour by shining it into an exotic, ultracooled cloud of sodium atoms. At
temperatures a fraction of a degree above absolute zero, the atoms
coalesce into a single quantum mechanical entity known as a Bose- 
Einstein
condensate. Shining a laser on the cloud tunes its optical properties so
that it becomes molasses when a second light pulse enters it.

Then, in 2001, Hau and a second team of physicists, this one from the
Harvard-Smithsonian Center for Astrophysics, brought light to a complete
halt by slowly turning off the laser. The Bose-Einstein cloud turned
opaque, trapping the light pulse inside. When the laser was turned back
on, the trapped light pulse flew out.

The latest results add an additional twist: transporting the pulse to a
second Bose-Einstein cloud and regenerating the light there.

"That's the sort of stuff we find really sexy in this business," said  
Eric
A. Cornell, a senior scientist at the National Institute of Standards  
and
Technology.

In the new Harvard experiment, when the initial pulse slammed into the
first Bose-Einstein cloud, the collision caused 50,000 to 100,000 of the
sodium atoms to start spinning, almost like small tops, and pushed this
small clump forward at less than a mile an hour.

Hau described the clump of atoms as a "metacopy" of the light pulse.
Although it consisted of sodium atoms instead of particles of light, it
exactly captured the characteristics of the light pulse.

The clump floated out from the rest of the cloud, traveled about
two-tenths of a millimeter and burrowed into a second Bose-Einstein  
cloud.
When a laser was shined on the second cloud, the atom clump transformed
into a new pulse of light identical to the original pulse.

It was refinements to the 2001 experimental technique that extended the
time the particles maintain quantum collective behavior. This allowed  
the
clump to reach the second cloud.

Pondering the applications
Transforming a light signal into a clump of atoms could be a way of
storing information. ("You could put it on the shelf for a while," Hau
said.) It could also enable a way of performing calculations in future
optical computers that employ quantum algorithms to speed through  
certain
types of calculations.

But one hurdle to building a computer that calculates with light is that
it is difficult to grab onto and manipulate a quick-moving light pulse.
Performing calculations with atomic clumps would be much easier with the
result changed back into light and then sped to the next step.

"That has been a missing link," Hau said.

The advance could also find applications in quantum cryptography, which
can hide messages in codes that cannot be broken.

Hau said the current apparatus was just a proof of the concept and far
from anything that could be used practically for any applications.

But that has not stopped other physicists from starting to ponder  
what the
applications might be, just as earlier experiments have spurred  
physicists
and engineers in a new active field of research, looking for ways to
harness slow light for use in optical networks.

Currently, optical signals need to be changed into electronic ones for
processing and then changed back into light. All-optical devices could
save on costs and power use.

Entire contents, Copyright © 2007 The New York Times. All rights  
reserved.


Copyright ©1995-2007 CNET Networks, Inc. All rights reserved.





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