IN RECENT years, innovative quantum tricks have slowed down light, even stopping it altogether. Now by switching the light source off at the right time it might be possible to use "slow light" as a new way to store information for use in quantum communications and computing.

In empty space, light travels at 300,000 kilometres per second. It goes a shade slower in glass and other materials, but physicists have found that light can be made extremely sluggish in dilute gases of atoms or in an exotic state of matter called a Bose-Einstein condensate.

In the case of a gas, the trick is first to use "control" lasers to put the atoms in a delicate quantum state that prevents them from interacting with light. This creates what physicists refer to as "electromagnetically induced transparency"- a condition in which compact pulses of light known as solitons can travel through the gas ...