Two years ago, researchers merely slowed light down to a pedestrian speed of 40 m.p.h. But now two Harvard research groups have independently brought light to a complete stop.

The latest experiment, which could pave the way for super-fast quantum computing, successfully brought light to a complete stop for half a millisecond. The normal speed of light is 186,000 miles per second.

The breakthroughs will be published in Nature next week and in Physical Review Letters on Jan. 29. Technology based on the discovery could be used in the future to make super-fast quantum computers or to send messages that are completely secure from hackers.

"The idea of quantum information is in its infancy," said David F. Phillips, an associate of the Harvard College Observatory at the Harvard-Smithsonian Center for Astrophysics and co-author of one of one of the studies. "We hope for wonderful things. Our imagination hasn't figured out what the possibilities are."

Phillips cautioned, however, that scientists are still "a long way" from using the discovery for practical applications such as quantum computing.

Phillips worked with the team led by Associates of the Harvard College Observatory Ronald L. Walsworth and Mikhail D. Lukin. Their paper will be published in Physical Review Letters. Another group, led by Associate of the Department of Physics Lene V. Hau, is publishing a similar study next week in Nature.

The new research is based in part on work by Hau published two years ago in Nature, in a study which brought light down to about 40 m.p.h.

The current study slowed light to a stop by shining it on super-cooled gaseous rubidium atoms. The atoms were bathed in laser light while a second beam was shined through them. By adjusting the intensity of the beams, the "fingerprint" of the second beam was imprinted on the electrons of the super-cooled atoms. In that state, the light was standing still.