June 26, 2012
In an independent experiment, an easier
approach was tried by the team of Ronald Walsworth and Mikhail Lukin at the
Harvard-Smithsonian Center for Astrophysics (CfA).
No supervacuum or ultra-cold was needed.
In fact, the chamber where the light stopped was at a temperature of
176 degrees F. 
To access the information, you turn on a control laser,
and out it comes. 
However, there appear to be clear
implications for using experiments like this to ultimately improve
the speed of computers, potentially creating the possibility to
shift from binary computing to quantum encoding of data.
Today’s machines represent information in bits, electronic combinations of zeros and ones. Bits represented by quantum states of atoms could carry much, much more information. Cubic inch for cubic inch, quantum computers could tackle problems that would stymie the most super of conventional computers.
For example, they could
perform many calculations simultaneously. 
Stop, Restart Light
January 24, 2001
to bring a light beam to a complete stop, then restart it again.
(Staff photo by Kris Snibbe)
Lene Hau isn't
talking about a used motorbike, but about light - that ethereal,
life-sustaining stuff that normally travels 93 million miles from
the sun in about eight minutes.
Working at the Rowland Institute for Science, overlooking the Charles River and the gold dome of the state Capitol in Boston, she and her colleagues slowed light 20 million-fold in 1999, to an incredible 38 miles an hour. They did it by passing a beam of light through a small cloud of atoms cooled to temperatures a billion times colder than those in the spaces between stars.
The atom cloud was suspended magnetically in a chamber pumped down to a vacuum 100 trillion times lower than the pressure of air in the room where you are reading this.
She and her team continued to tweak their system until they finally brought light to a complete stop.
The light dims as it slows down, so you
think that it's being turned out. Then Hau shoots a yellow-orange
laser beam into the cloud of atoms, and the light emerges at full
speed and intensity.
That team was headed by Ronald Walsworth and Mikhail Lukin, both associates of Harvard College.
Their success was independent of Hau's effort.
These include vastly more powerful computers as well as the possibility of communications that are much more secure from hackers and people trying to steal your credit and bank card numbers.
Hau, a tall, slender scientist educated as a theoretical physicist in Denmark, had a hunch several years ago that intensely cold atoms would become a hot area in physics.
In the mid-1990s, she and her colleagues became excited about experiments aimed at crowding atoms so close together that unusual things happen. The key is to cool them to within a billionth of a degree of minus 459.7 degrees F.
Called "absolute zero," this is the
temperature at which atoms have the least possible energy, and they
all but cease to move around.
The laser beams glow yellow-orange like
sodium streetlights, and the cigar-shaped cloud of atoms is about
eight-thousandths of an inch long and about a third as wide.
When that laser is
switched on again, it abruptly frees the light from the trap and it
goes on its way.
The laser illuminating the cloud at
right angles to the incoming beam acts like a parking brake,
stopping the beam inside the cloud when it is shut off. When it is
turned on again, the brake is released, the atoms transfer their
energy back to the light, and it leaves the end of the cloud at full
speed and intensity.
The CfA researchers used an easier method.
They shot laser beams through a dense
cloud of rubidium and helium gas. (Rubidium, in its solid or natural
form, is a soft, silver-white metal.) The light bounced from atom to
atom, gradually slowing down until it stopped. No supervacuum or
ultra-cold was needed. In fact, the chamber where the light stopped
was at a temperature of 176 degrees F.
To access the information, you turn on a control laser, and out it comes.
Today's machines represent information in bits, electronic combinations of zeros and ones.
Bits represented by quantum states of
atoms could carry much, much more information. Cubic inch for cubic
inch, quantum computers could tackle problems that would stymie the
most super of conventional computers. For example, they could
perform many calculations simultaneously.
These would be built on chips no bigger than the Pentium IV that runs many of today's small laptop and palm-sized computers.
She and her colleagues describe their experiment in detail in today's issue of the journal Nature.
Opens The Way to New Computers and
Communication Systems -
February 8, 2007
from HarvardGazetteUniversity Website
recovered through WayBackMachine Website
Lene Hau Explains How She Stops Light in One Place
Then Retrieves and
Speeds it Up in A Completely Separate Place
Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can't be speeded-up or slowed down.
But in 1998, Hau, for the first time in
history, slowed light to 38 miles an hour, about the speed of
She and her team made a light pulse
disappear from one cold cloud then retrieved it from another cloud
nearby. In the process, light was converted into matter then back
into light. For the first time in history, this gives science a way
to control light with matter and vice versa.
Some colleagues had asked Hau,
In the experiment, a light pulse was slowed to bicycle speed by beaming it into a cold cloud of atoms.
The light made a "fingerprint" of itself in the atoms before the experimenters turned it off. Then Hau and her assistants guided that fingerprint into a second clump of cold atoms.
And get this - the clumps were not touching and no light passed between them.
The experimenters then nudged the second cloud of atoms with a laser beam, and the atomic imprint was revived as a light pulse.
The revived light had all the characteristics present when it entered the first cloud of atomic matter, the same shape and wavelength. The restored light exited the cloud slowly then quickly sped up to its normal 186,000 miles a second.
That information can be stored - put on
a shelf, so to speak - retrieved at will, and converted back to
light. The retrieved light would contain the same information as the
original light, without so much as a period being lost.
A weird thing happens to the light as it enters the cold atomic cloud, called a Bose-Einstein condensate.
It becomes squeezed into a space 50
million times smaller. Imagine a light beam 3,200 feet (one
kilometer) long, loaded with information, that now is only a hair
width in length but still encodes as much information.
When a laser beam enters such a
condensate, the light leaves an imprint on a portion of the atoms.
That imprint moves like a wave through the cloud and exits at a
speed of about 700 feet per hour. This wave of matter will keep
going and enter another nearby ultracold condensate. That's how
light moves darkly from one cloud to another in Hau's laboratory.
To make a long story short, information
in this form can be made absolutely tamper proof. Personal
information would be perfectly safe.
Details of the experiments appear as the cover story of the Feb. 8 issue of Nature. Authors of the report include graduate student Naomi Ginsberg, postdoctoral fellow Sean Garner, and Hau.
Despite all the intriguing possibilities,
However, she has no doubt that practical systems will come. And when they do, they will look completely different from anything we are familiar with today.
They won't need a lot of wires and electronics.
Creating those ultracold atomic clouds in a factory, office, or recreation room will be a problem, but one she believes can be solved.
There are no "maybes" in Hau's voice.
She is coolly confident that
light-to-matter communication networks, codes, clocks, and guidance
systems can be made part of daily life. If you doubt her, remember
she is the person who stopped light, converted it to matter, carried
it around, and transformed it back to light.