-Caveat Lector- Forwarded without comment. Tenorlove ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~` > http://partners.nytimes.com/2001/01/18/science/18LIGH.html?Partner=AltaVista > &RefId=_WLmY_WEFnnunuu-ly > January 18, 2001 > Scientists Bring Light to Full Stop, Hold It, Then Send It on Its Way > By JAMES GLANZ > > > The New York Times > > ---------------------------------------------------------------------------- > researchers say they have slowed light to a dead stop, stored it and > then > released it as if it were an ordinary material particle. > > The achievement is a landmark feat that, by reining in nature's > swiftest and > most ethereal form of energy for the first time, could help realize > what are > now theoretical concepts for vastly increasing the speed of computers > and > the security of communications. > > Two independent teams of physicists have achieved the result, one led > by Dr. > Lene Vestergaard Hau of Harvard University and the Rowland Institute > for > Science in Cambridge, Mass., and the other by Dr. Ronald L. Walsworth > and > Dr. Mikhail D. Lukin of the Harvard-Smithsonian Center for > Astrophysics, > also in Cambridge. > > Light normally moves through space at 186,000 miles a second. > Ordinary > transparent media like water, glass and crystal slow light slightly, > an > effect that causes the bending of light rays that allows lenses to > focus > images and prisms to produce spectra. > > Using a distantly related but much more powerful effect, the > Walsworth-Lukin > team first slowed and then stopped the light in a medium that > consisted of > specially prepared containers of gas. In this medium, the light > became > fainter and fainter as it slowed and then stopped. By flashing a > second > light through the gas, the team could essentially revive the original > beam. > > The beam then left the chamber carrying nearly the same shape, > intensity and > other properties it had when it entered. The experiments led by Dr. > Hau > achieved similar results with closely related techniques. > > "Essentially, the light becomes stuck in the medium, and it can't get > out > until the experimenters say so," said Dr. Seth Lloyd, an associate > professor > of mechanical engineering at the Massachusetts Institute of > Technology who > is familiar with the work. > > Dr. Lloyd added, "Who ever thought that you could make light stand > still?" > > He said the work's biggest impact could come in futuristic > technologies > called quantum computing and quantum communication. Both concepts > rely > heavily on the ability of light to carry so-called quantum > information, > involving particles that can exist in many places or states at once. > > Quantum computers could crank through certain operations vastly > faster than > existing machines; quantum commmunications could never be > eavesdropped upon. > For both these systems, light is needed to form large networks of > computers. > But those connections are difficult without temporary storage of > light, a > problem that the new work could help solve. > > A paper by Dr. Walsworth, Dr. Lukin and three collaborators - Dr. > David > Phillips, Annet Fleischhauer and Dr. Alois Mair, all at Harvard- > Smithsonian - is scheduled to appear in the Jan. 29 issue of Physical > Review > Letters. > > Citing restrictions imposed by the journal Nature, where her report > is to > appear, Dr. Hau refused to discuss her work in detail. > > Two years ago, however, Nature published Dr. Hau's description of > work in > which she slowed light to about 38 miles an hour in a system > involving beams > of light shone through a chilled sodium gas. > > Dr. Walsworth and Dr. Lukin mentioned Dr. Hau's new work in their > paper, > saying she achieved her latest results using a similarly chilled gas. > Dr. > Lukin cited her earlier work, which Dr. Hau produced in collaboration > with > Dr. Stephen Harris of Stanford University, as the inspiration for the > new > experiments. > > Those experiments take the next step, stopping the light's > propagation > completely. > > "We've been able to hold it there and just let it go, and what comes > out is > the same as what we sent in," Dr. Walsworth said. "So it's like a > freeze > frame." > > Dr. Walsworth, Dr. Lukin and their team slowed light in a gas form of > rubidium, an alkaline metal element. > > The deceleration of the light in the rubidium differed in several > ways from > how light slows through an ordinary lens. For one thing, the light > dimmed as > it slowed through the rubidium. > > Another change involved the behavior of atoms in the gas, which > developed a > sort of impression of the slowing wave. > > This impression, actually consisting of patterns in a property of the > atoms > called their spin, was a kind of record of the light's passing and > was > enough to allow the experimenters to revive or reconstitute the > original > beam. > > Both Dr. Hau's original experiments on slowing light, and the new > ones on > stopping it, rely on a complex phenomenon in certain gases called > electromagnetically induced transparency, or E.I.T. > > This property allows certain gases, like rubidium, that are normally > opaque > to become transparent when specially treated. > > For example, rubidium would normally absorb the dark red laser light > used by > Dr. Walsworth and his colleagues, because rubidium atoms are easily > excited > by the frequency of that light. > > But by shining a second laser, with a slightly different frequency, > through > the gas, the researchers rendered it transparent. > > The reason is that the two lasers create the sort of "beat frequency" > that > occurs when two tuning forks simultaneously sound slightly different > notes. > > The gas does not easily absorb that frequency, so it allows the light > to > pass through it; that is, the gas becomes transparent. > > But another property of the atoms, called their spin, is still > sensitive to > the new frequency. Atoms do not actually spin but the property is a > quantum-mechanical effect analagous to a tiny bar magnet that can be > twisted > by the light. > > As the light passes through, it alters those spins, in effect > flipping them. > Though the gas remains transparent, the interaction serves as a > friction or > weight on the light, slowing it. > > Using that technique, Dr. Hau and Dr. Harris in the earlier > experiment > slowed light to a crawl. But they could not stop it, because the > transparent > "window" in the gas became increasingly narrower, and more difficult > to pass > through, as the light moved slower and slower. > > In a recent theoretical advance, Dr. Lukin, with Dr. Suzanne Yelin of > Harvard-Smithsonian and Dr. Michael Fleischhauer of the University of > Kaiserslautern in Germany, discovered a way around this constraint. > > They suggested waiting for the beam to enter the gas container, then > smoothly reducing the intensity of the second beam. > > The three physicists calculated that this procedure would narrow the > window, > slowing the first beam, but also "tune" the system so that the beam > always > passes through. > > The first beam, they theorized, should slow to an infinitesimally > slow > speed, finally present only as an imprint on the spins, with no > visible > light remaining. Turning the second beam back on, they speculated, > should > reconstitute the first beam. > > The new experiments bore those ideas out. > > "The light is actually brought to a stop and stored completely in the > atoms," Dr. Harris said. "There's no other way to do that. It's been > done - > done very convincingly, and beautifully." __________________________________________________ Do You Yahoo!? Yahoo! Auctions - Buy the things you want at great prices. http://auctions.yahoo.com/ <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! These are sordid matters and 'conspiracy theory'—with its many half-truths, mis- directions and outright frauds—is used politically by different groups with major and minor effects spread throughout the spectrum of time and thought. 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