by admin

June 26, 2012
from WakingTimes Website

 

 

 


 


In two independent experiments that defy the notions of Einstein, researchers have been able to stop, then restart a beam of light.

Ordinarily, light travels at the speed of 186,282 miles per second, but the research team of Lene Hau, a professor of physics at Harvard, who in 1999 was able to slow light down to 38 miles per hour, has been able to trap light in a cloud of sodium atoms super-cooled to near ‘absolute zero.’

“It’s nifty to look into the chamber and see a clump of ultracold atoms floating there,” Hau says. “In this odd state, light takes on a more human dimension; you can almost touch it.” [1]

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).

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. [1]

Both experiments accomplish almost the same thing, however, in the CfA experiment researchers were only able to store about half of the incoming light, and the storage time was about half that of Hau’s experiment.

Think of both contraptions as sophisticated light switches that control not just light but information. Incoming light can carry information expressed by changes or modulations of its frequency, amplitude, and phase. When the light stops, that information is stored just like information is stored in the electronic memory of a computer.

 

To access the information, you turn on a control laser, and out it comes. [1]

Remarkably, scientists are somewhat uncertain about the implications and practicality of this research.

“We hope for wonderful things,” says David Phillips, who worked on the CfA 'stop light' project. “Our imagination hasn’t figured out what the possibilities are yet.” [1]

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.

Computers operating by these so-called quantum effects are much more efficient that those available today, or even on the drawing board. (“Quantum” refers to changes in the energy levels of the atoms.)

 

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. [1]

The eminent physicist Albert Einstein theorized that it was impossible for light to travel at a speed faster than 186,282 miles per second, and in this case he has not yet been proven wrong.

Watch the following video for amazing footage of Hau’s research:

 

 

 

 


 

 

 

Source

[1] Researchers Now Able to Stop, Restart Light

     Light and Matter United - Opens The Way to New Computers and Communication Systems

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



 Researchers Now Able to...

Stop, Restart Light
by William J. Cromie
Gazette Staff

January 24, 2001
from HarvardGazetteUniversity Website

 


 


Lene Hau and her colleagues created a new form of matter

 to bring a light beam to a complete stop, then restart it again.

 (Staff photo by Kris Snibbe)

 

"Two years ago we slowed it down to 38 miles an hour; now we've been able to park it then bring it back up to full speed."

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.

Less than five years ago, the speed of light was considered one of the universe's great constants. Albert Einstein theorized that light cannot travel faster than 186,282 miles per second. No one has proved him wrong, but he never said that it couldn't go slower.

Hau, 41, a professor of physics at Harvard, admits that the famous genius would "probably be stunned" at the results of her experiments.

 

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.

"It's nifty to look into the chamber and see a clump of ultracold atoms floating there," Hau says. "In this odd state, light takes on a more human dimension; you can almost touch it."

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.

Inspired by Hau's success at slowing light, researchers working on a wooded hill a few miles away at the Harvard-Smithsonian Center for Astrophysics (CfA) used a similar technique to stop, then restart, a light beam.

 

That team was headed by Ronald Walsworth and Mikhail Lukin, both associates of Harvard College.

 

Their success was independent of Hau's effort.

"We didn't have much contact," she notes, "just a few e-mails."

 


Stopping cold

Besides stirring a research rush to explore exotic forms of matter, such experiments open the door to some practical applications.

 

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.

"We hope for wonderful things," says David Phillips, who worked on the CfA "stop light" project. "Our imagination hasn't figured out what the possibilities are yet."

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.

Hau was one of several researchers who succeeded in creating this novel state of matter. She corresponded with a colleague, Stepen Harris at Stanford University, and they came up with the idea that it might be possible to use a small ball of cold atoms to slow down light.

Hau and her group then figured out a way to make it work. Using sodium atoms and two laser beams, they made a new kind of medium that entangles light and slows it down.

 

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.

Working with Chien Liu, a postdoctoral fellow at Rowland, and Harvard graduate students Zachary Dutton and Cyrus Behroozi, Hau kept tweaking the atoms until they completely stopped laser light. This happens when a second laser beam directed at right angles to the cloud of atoms is cut off.

 

When that laser is switched on again, it abruptly frees the light from the trap and it goes on its way.

Hau explains that light entering the atomic entanglement transfers its energy to the atoms. Light energy raises the atoms to higher energy levels in ways that depend on the frequency and intensity of the light.

 

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.

Hau's team stopped light for one-thousandth of a second.

 

Atomically speaking,

"this is an amazingly long time," Hau notes. "But we think it can be stopped for much longer."

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.

This convenience comes at a cost, however. Only half of the incoming light was stored, then recovered, and the storage time was much shorter.

Think of both contraptions as sophisticated light switches that control not just light but information. Incoming light can carry information expressed by changes or modulations of its frequency, amplitude, and phase. When the light stops, that information is stored just like information is stored in the electronic memory of a computer.

 

To access the information, you turn on a control laser, and out it comes.

 

 

 

 

 

 

 

 


Shrinking computers

Computers operating by these so-called quantum effects are much more efficient that those available today, or even on the drawing board. ("Quantum" refers to changes in the energy levels of the atoms.)

 

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.

Another thing they could do would be to encrypt information in complex codes impossible to crack without extremely expensive and time-consuming methods. Financial and other information would be prodigiously safer with a quantum computer.

As marvelous as they are, however, both the Rowland and CfA systems take up more space and power than would be practical. Hau's experiment requires a small room, CfA's needs a large tabletop.

CfA researchers need to solve this problem and to make sure all the light is stored - not just half. That will take many years.

Hau has already started ordering and installing equipment with which she plans to construct a quantum light stopper no bigger than a fingernail. She envisions ultracold and supervacuums being achieved with devices less than one-thousandth of an inch in size.

 

These would be built on chips no bigger than the Pentium IV that runs many of today's small laptop and palm-sized computers.

"Wouldn't that be nifty!" Hau says.

She and her colleagues describe their experiment in detail in today's issue of the journal Nature.

 

 

 

 

 

 

 

 



 Light and Matter United

-   Opens The Way to New Computers and Communication Systems   -
by William J. Cromie
Harvard News Office

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
Staff photo Justin Ide/Harvard News Office

 


Lene Hau has already shaken scientists' beliefs about the nature of things.

 

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 rush-hour traffic.

Two years later, she brought light to a complete halt in a cloud of ultracold atoms. Next, she restarted the stalled light without changing any of its characteristics, and sent it on its way. These highly successful experiments brought her a tenured professorship at Harvard University and a $500,000 MacArthur Foundation award to spend as she pleased.

Now Mallinckrodt Professor of Physics and of Applied Physics, Hau has done it again.

 

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.

It's a thing that most scientists never thought was possible.

 

Some colleagues had asked Hau,

"Why try that experiment? It can't be done."

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 two atom clouds were separated and had never seen each other before," Hau notes. They were eight-thousandths of an inch apart, a relatively huge distance on the scale of atoms.

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.

 

 

 

 

 

 

 

 


Communicating by light

Light carries information, so think of information being manipulated in ways that have never before been possible.

 

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.

Or the information could be changed.

"The light waves can be sculpted," is the way Hau puts it. "Then it can be passed on. We have already observed such re-sculpted light in our lab."

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.

From there it becomes easier to imagine new types of computers and communications systems - smaller, faster, more reliable, and tamper-proof.

Atoms at room temperature move in a random, chaotic way. But when chilled in a vacuum to about 460 degrees below zero Fahrenheit, under certain conditions millions of atoms lock together and behave as a single mass.

 

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.

This invisible wave of matter keeps going unless it's stopped in the second cloud with another laser beam, after which it can be revived as light again.

Atoms in matter waves exist in slightly different energy levels and states than atoms in the clouds they move through. These energy states match the shape and phase of the original light pulse.

 

To make a long story short, information in this form can be made absolutely tamper proof. Personal information would be perfectly safe.

Such a light-to-matter, matter-to-light system,

"is a wonderful thing to wrap your brain around," Hau muses.

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.

 

 

 


In a practical manner

You won't see a light-matter converter flashing away in a factory, business, or mall anytime soon.

 

Despite all the intriguing possibilities,

"there are no immediate practical uses," Hau admits.

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.

"Instead of light shining through optical fibers into boxes full of wires and semiconductor chips, intact data, messages, and images will be read directly from the light," Hau imagines.

Creating those ultracold atomic clouds in a factory, office, or recreation room will be a problem, but one she believes can be solved.

"The atomic clouds we use in our lab are only a tenth of a millimeter (0.004 inch) long," she points out.

 

"Such atom clouds can be kept in small containers, not all of the equipment has to be so cold. Most likely, a practical system designed by engineers will look totally unlike the setup we have in our lab today."

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.