Two independent teams of scientists have found a way to reduce the speed of light to zero. Although light in a vacuum moves at a neck-breaking 186,000 miles a second, materials with a high refractive index can slow it down. Lene Vestergaard Hau of Harvard University and colleagues managed to stall the progress of a laser beam completely by passing it through a supercold gas. They first created a cloud of several million sodium atoms, cooled to within a few millionths of a degree from absolute zero and held in a magnetic atom trap. Normally such a gas wouldn't let any light pass. So the scientists cut a path through it using a laser beam called a coupling beam. Next they shot through a probe laser pulse at a specific wavelength. When the pulse was midway through the gas, they shut off the coupling beam--stopping the probe beam dead in its tracks. When they turned the coupling beam back on, the probe beam continued on its way.

The ability to bring light to an utter standstill could find ample use in quantum computers. Such devices promise to carry out an array of tasks more efficiently and faster than ordinary machines by storing information in quantum states, such as those of the individual photons in a laser beam. Hau's work--which builds on her accomplishment two years ago of slowing light to about 38 miles an hour--will appear in a future issue of Nature. The other group--Ronald Walsworth, Mikhail Lukin and colleagues at the Harvard-Smithsonian Center for Astrophysics--will publish their like result in the January 29th issue of Physical Review Letters.