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With 'slow light,' the promise of low-power, all-optical data networks

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A DARPA-funded optical device built into a silicon chip can reduce the speed of light by a factor of 1,200, a major step toward the realization of an ultra-efficient, all-optical quantum data network.

A tiny optical device built into a silicon chip can reduce the speed of light by a factor of 1,200, a major step toward the realization of an ultra low-power, all-optical quantum data network.

The device achieved the feat -- the slowest light propagation on a chip to date, by the way -- with the help of quantum interference effects in a rubidium vapor inside a hollow-core optical waveguide built into a conventional silicon chip.

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Researchers have used many different techniques to slow the speed of light, including those using quantum interference effects. But those systems required low temperatures or elaborate laboratory setups.

This new atomic spectroscopy chip changes that.

Here's how it works: a control laser modifies the optical properties of the rubidium vapor in the hollow-core waveguide. Under the combined action of two laser fields -- control and signal -- electrons in the rubidium atoms are transferred into a coherent superposition of two quantum states.

In other words, they exist in two different states at the same time.

That results in an effect called electromagnetically induced transparency, which is key to producing what is called "slow light."

The process also produces other interactions between light and matter, which open the door for radically different optical devices for quantum computing and quantum communication systems, according to the researchers.

Better still, the researchers can change the speed of light by simply changing the power of the control laser.

If none of this makes sense to you, take only this fact with you: this accomplishment -- the first demonstration of electromagnetically induced transparency and slow light on a fully self-contained atomic spectroscopy chip -- potentially allows for major improvements in the performance of communication networks.

Why? Because the optical fibers we use today can transmit data at light speed, but the devices we use to route and process that data still requires converting those light signals to electronic signals.

This development -- on a platform that works at room temperature and can be mass-produced, no less -- takes us a step closer to that holy grail.

The research team was led by University of California Santa Cruz professor Holger Schmidt and comprised of researchers from UC Santa Cruz and Brigham Young University. Their work was funded by the National Science Foundation and the Defense Advanced Research Projects Agency, or DARPA.

Their findings were published in the Nov. 2010 issue of the journal Nature Photonics.

Photo: A four-inch silicon wafer with 32 integrated atomic spectroscopy chips. (C. Lagattuta/UCSC)

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Andrew Nusca

Editor Emeritus

Andrew Nusca is editor of SmartPlanet and an associate editor for ZDNet. Previously, he worked at Money, Men's Vogue and Popular Mechanics magazines. He holds degrees from the Columbia University Graduate School of Journalism and New York University. He is based in New York but resides in Philadelphia. Follow him on Twitter. Disclosure