A Stoplight for Light

"Two years ago we slowed it down to 38 miles an hour; now we've been able to park it then bring it back up to full speed." Lene Hau isn't talking about a used motorbike, but about light – that ethereal, life-sustaining stuff that normally travels 93 million miles from the sun in about eight minutes.

Less than five years ago, the speed of light was considered one of the universe's great constants. Albert Einstein theorized that light cannot travel faster than 186,282 miles per second. No one has proved him wrong, but he never said that it couldn't go slower. ...

Using sodium atoms and two laser beams, they made a new kind of medium that entangles light and slows it down. The laser beams glow yellow-orange like sodium streetlights, and the cigar-shaped cloud of atoms is about eight-thousandths of an inch long and about a third as wide.

Working with Chien Liu, a postdoctoral fellow at Rowland, and Harvard graduate students Zachary Dutton and Cyrus Behroozi, Hau kept tweaking the atoms until they completely stopped laser light. This happens when a second laser beam directed at right angles to the cloud of atoms is cut off. When that laser is switched on again, it abruptly frees the light from the trap and it goes on its way. More...