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Light pulse hovers in atom capsule

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5:59pm, January 11, 2004
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In the past few years, physicists have shown that they can bring light pulses to a dead stop. That feat relies on a method of temporarily imprinting the quantum essence of a pulse by changing certain characteristics of atoms (SN: 2/9/02, p. 94: Available to subscribers at Light comes to halt again—in a solid). Now, physicists have demonstrated stationary light by a new method.

The innovation preserves the optical energy of an immobile pulse. Such pulses could prove useful for making circuits that manipulate photons instead of electrons and for light-based, quantum computers that would exploit aspects of quantum mechanics to outperform today's computers.

In the Dec. 11, 2003 Nature, Mikhail D. Lukin of Harvard University and his colleagues describe the new procedure for putting light in suspended animation. They start with the previously developed method: They shine a laser on hot rubidium gas in a glass cylinder about the size of an AAA battery. Then, the scientists shoot another laser pulse into the cylinder. When the first, or control, laser suddenly turns off, the second laser imprints the quantum identity of its red pulses onto the rubidium atoms, effectively storing the red light.

Researchers typically resurrect such imprinted pulses by restarting the control laser. In the new experiment, however, the scientists did that and simultaneously turned on another control laser beaming into the rubidium cloud from the opposite direction. This procedure restored the red pulse as a blob of optical energy and created an interference pattern.

Influenced by that radiation pattern, the rubidium atoms behaved "like a stack of mirrors" that bounced the pulse back and forth for tens of microseconds, notes Marlan O. Scully of Princeton University in a commentary in the same issue of Nature. That might be long enough for researchers to explore how such pulses might interact with other pulses of stopped light and even with moving light, Lukin says.

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