Light and matter united

http://www.npr.org/templates/story/story.php?storyId=7314502

Lene Hau was able to slow light to 17 metres per second, and, in 2001, was able to momentarily stop a beam by passing it through a transparent superfluid --Bose-Einstein Condensate--a state of matter that only exists at near absolute zero temperatures.
Dr. Hau and her associates at Harvard University have successfully transformed light into matter and back into light using Bose–Einstein condensates. Details of the experiment are discussed in the February 8, 2007 publication of the journal Nature.[1]
"Light and matter united", by William J. Cromie, Harvard University Gazette, February 7, 2007.
^ Coherent control of optical information with matter wave dynamics, Ginsberg, Garner and Hau. Nature, 445, 623-626 (8 February 2007) | doi:10.1038/nature05493; Received 23 October 2006; Accepted 24 November 2006.
Hau Lab at Harvard
Story from NPR.org describing her group's efforts which resulted in being able to convert light to matter and back again in a Bose–Einstein condensate

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Ultra Slow and Stopped Light

In 1998, we succeeded in reducing the light speed to 17 m/s by creating a laser induced quantum interference in a Bose-Einstein condensate (BEC). The low light speeds are obtained in an optical medium created from entangled states between Bose condensed atoms and a laser field. The intensity of this light field controls the optical properties for another, pulsed laser beam sent through the medium. The reported reduction of the pulse propagation speed by a factor of 20 million is associated with a spatial compression of the laser pulses in the condensate by the same factor. Furthermore, the established quantum interference allows for lossless, shape preserving transmission of light pulses through atomic media that would otherwise be totally opaque.

For more, see our ultra-slow light paper here:
http://www.seas.harvard.edu/haulab/publications/pdf/Slow_Light_1999.pdf

Soon after, we succeeded in stopping a light pulse completely in an atomic cloud cooled to a temperature just above the transition temperature for BEC. At the time when the light pulse is slowed, compressed, and contained within the atomic sample, we turn off the control laser field abruptly and then turn it back on at a later time. When the control laser is turned back on, the light pulse is regenerated: we can stop and controllably regenerate the light pulse. During the storage time, thermal motion and associated smearing of the optical information imprinted in the atoms are minimized with the use of ultracold atoms.

For more, see our stopped light paper here:
http://www.seas.harvard.edu/haulab/publications/pdf/Stopped_Light_2001.pdf

We have used slow and stopped light in Bose-Einstein condensates for generation of quantum shock waves in superfluids, for optical processing, and for creation of a pulsed atom laser.






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HARVARD GAZETTE ARCHIVES

Lene Hau transformed light into matter and back into light
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

Light and matter united
Opens the way to new computers and communication systems
By William J. Cromie
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.


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• Video: Light and matter (2007) (1:52)
http://www.hno.harvard.edu/multimedia/flash/vid_hau2007.swf

• Video: Light stopper (2001) (2:52)
http://www.hno.harvard.edu/multimedia/flash/vid_hau2001.swf

• More multimedia

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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.

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http://www.nature.com/nature/journal/v409/n6819/full/409490a0.html

Nature 409, 490-493 (25 January 2001) | doi:10.1038/35054017; Received 13 October 2000; Accepted 17 November 2000

Observation of coherent optical information storage in an atomic medium using halted light pulses
Chien Liu1,2, Zachary Dutton1,3, Cyrus H. Behroozi1,2 and Lene Vestergaard Hau 1,2,3

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Nature 445, 623-626 (8 February 2007) | doi:10.1038/nature05493; Received 23 October 2006; Accepted 24 November 2006


Coherent control of optical information with matter wave dynamics
Naomi S. Ginsberg1, Sean R. Garner1 & Lene Vestergaard Hau 1

Department of Physics, and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
Correspondence to: Correspondence and requests for materials should be addressed to L.V.H. (Email: hau@physics.harvard.edu).

Abstract:
In recent years, significant progress has been achieved in manipulating matter with light, and light with matter1. Resonant laser fields interacting with cold, dense atom clouds provide a particularly rich system2, 3, 4, 5, 6. Such light fields interact strongly with the internal electrons of the atoms, and couple directly to external atomic motion through recoil momenta imparted when photons are absorbed and emitted. Ultraslow light propagation in Bose–Einstein condensates7 represents an extreme example of resonant light manipulation using cold atoms. Here we demonstrate that a slow light pulse can be stopped and stored in one Bose–Einstein condensate and subsequently revived from a totally different condensate, 160 m away; information is transferred through conversion of the optical pulse into a travelling matter wave. In the presence of an optical coupling field, a probe laser pulse is first injected into one of the condensates where it is spatially compressed to a length much shorter than the coherent extent of the condensate. The coupling field is then turned off, leaving the atoms in the first condensate in quantum superposition states that comprise a stationary component and a recoiling component in a different internal state. The amplitude and phase of the spatially localized light pulse are imprinted on the recoiling part of the wavefunction, which moves towards the second condensate. When this 'messenger' atom pulse is embedded in the second condensate, the system is re-illuminated with the coupling laser. The probe light is driven back on and the messenger pulse is coherently added to the matter field of the second condensate by way of slow-light-mediated atomic matter-wave amplification. The revived light pulse records the relative amplitude and phase between the recoiling atomic imprint and the revival condensate. Our results provide a dramatic demonstration of coherent optical information processing with matter wave dynamics. Such quantum control may find application in quantum information processing and wavefunction sculpting.


Matter and light are different forms of the same "stuff"...just as we can describe ice as frozen  water, and water as melted ice.