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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Wednesday, February 07, 2007

Store Light Here and Retrieve It at a Distance

Lene Vestergaard Hau, Mallinckrodt Professor of Physics and of Applied Physics [Photo courtsey: Jay Penni Photography, Harvard Univ]

In Bose-Einstein condensates (BECs), atoms are cooled to such low temperatures that they all occupy the same quantum state, even though they may be physically apart from each other. Making use of such quantum mechanically indistinguishable microscopic particles, Lene Hau and colleagues from Harvard University have been able to imprint a coherent pulse of light on a collection of ultracold atoms -- and then retrieve the same light pulse from a second set of atoms that is some distance away.

"We demonstrate that we can stop a light pulse in a supercooled sodium cloud, store the data contained within it, and totally extinguish it, only to reincarnate the pulse in another cloud two-tenths of a millimeter away," announced Lene Hau. In a paper published in Feb 8 issue of 'Nature', Lene Hau and her co-authors, Naomi S. Ginsberg and Sean R. Garner, reported their spectacular finding that the light pulse can be revived, and its information transferred between the two clouds of sodium atoms (or, the Bose-Einstein condensates -- illuminated with a control laser and cooled to just billionths of a degree above absolute zero), by converting the original optical pulse into a traveling matter wave. The matter wave is a matter-copy of the original pulse, traveling at a leisurely 200 meters per hour. When the matter pulse enters the second of the supercooled clouds which is illuminated with a control laser, it is readily converted back into light.

The results of this experiment provide a powerful means of controlling optical information and certainly will lead a way to future directions of optical communication. It could also have applications in the developing fields of quantum information processing and quantum cryptography.

"Coherent control of optical information with matter wave dynamics"
Naomi S. Ginsberg, Sean R. Garner and Lene Vestergaard Hau

Nature 445, 623-626 (8 February 2007) Link to Abstract

Background Reading
Wikipedia page on Bose-Einstein Condensate
BEC homepage, JILA, Colorado
2Physics past posting on BEC

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