DARPA-Funded Device Adjusts the Speed of Light With the Twist of a Knob

UC Santa Cruz's 'Slow Light' Device

The small stuff (left) adds up to a 4-inch silicon wafer with 32 atomic spectroscopy cells (right).Nature Photonics

DARPA has asked a lot from the science and tech communities, requesting everything from flying cars to weather manipulation to suspended animation. Now they've asked UC Santa Cruz researchers to slow down the speed of light, and in a breakthrough that could reshape optical communications, researchers have done exactly that.

Built into a silicon chip, the small optical device has slowed the speed of light by a factor of 1,200 in the lab, in conditions that were previously unthinkable -- that is, under normal conditions. "Slow light," as it's known, has been produced before, but usually it requires special, lab-induced conditions – often at very low temperatures – that were too complicated for practical use. The UC Santa Cruz team designed their device to work at room temperature and to be produceable in market quantities.

The device relies on quantum interference effects on photons (click through to Nature Photonics for the long explanation) as they move through a waveguide built into a chip. These effects don't just produce slower light, but also lead to other interesting interaction between light and matter that could lead to a variety of applications in optical devices, communications, and computing.

Moreover, it's easily tunable. A control laser governs the degree to which the light is slowed, so it's easy to adjust by simply changing the energy of the laser – turn a knob, slow the speed of light. Turn it the other way, increase the speed of light.

Manipulating light with the twist of a knob. Kind of makes you feel all-powerful, doesn't it? Now, how are things coming along on that weather-control machine?