DARPA alters the speed of light

Quantum mechanics used in the development of photonic microchip

Researchers at the Defense Advanced Research Projects Agency have found a way to change the speed of light -- very, very slightly.

The boffins have developed a prototype photonic microchip that uses light instead of electrons to transmit data. The chip uses quantum effects to slow down or stop photons, allowing the device to operate at speeds and efficiencies similar to fiber optic links. Such developments could lead to smaller, faster computers, sensors and communications systems that can overcome the limitations of current electronics, according to scientists.

Funded by DARPA and the National Science Foundation, the integrated Photonic Delay (iPhoD) program is developing technologies that could soon be used in a variety of military and civil applications. Holger Schmidt, a professor at the School of Engineering at the University of California Santa Cruz, is leading the team, which used commercially available microprocessors to create the device.

According to Schmidt, the iPhoD operates by using quantum interference effects in a rubidium vapor inside a hollow core optical waveguide built into a silicon chip with standard manufacturing methods. “We can change the speed of light — just by turning the power control knob,” he told the Register.

Schmidt said that scientists have known about slow light and other quantum coherence effects for some time, but to use the effect practically, they need to find a way to mass-produce it on a device that can operate at room temperatures or higher. The team’s iPhoD chip is able to accomplish that feat.

Slowlight can be used, for example, to provide a data buffer or tunable signal delay in an optical network, he said.

The rubidium vapor will normally absorb the light from the signal laser, preventing any photons from getting through. But when a control laser is activated, the material becomes transparent, permitting the signal pulse to pass through at less than the speed of light. “We can potentially use this to create all-optical switches, single-photon devices, quantum-memory devices, and other exciting possibilities,” Schmidt said.

However, the effect is useful only for data, so no starships, TARDISes or time portals are likely to come from the research.

A white paper detailing the team's research has been published on the Nature Web site.

Reader Comments

Wed, Sep 8, 2010 Michael Alexander AF Research Lab, Sensors Directorate, Hanscom AFB, MA

Every time you look through eyeglasses, binoculars, or a refracting telescope, or any other lens-based device (including your own eye) that alters the direction of a beam of light, you encounter slowed light. Slowed light, as such, is far from new. The quantum mechanical action in specially prepared rubidium vapors, reported in your article, was discovered several years ago by Professor Lene Hau of Harvard, who "stopped" and "restarted" a beam of light. Others, using different methods, have subsequently performed similar feats. So what is DARPA bringing to the table? Judging from the article, DARPA's contribution will be to underwrite engineering of the phenomenon in order to create certain practical photonic devices.

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