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 鈥渟low light鈥� 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 鈥渃ontrol鈥� lasers to put the atoms in a delicate quantum state that prevents them from interacting with light. This creates what physicists refer to as 鈥渆lectromagnetically induced transparency鈥�- a condition in which compact pulses of light known as solitons can travel through the gas without exchanging any energy with it. The soliton鈥檚 speed depends on the intensity of the control lasers, and by turning this down researchers can slow the soliton or even bring it to a halt.
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Now a team led by physicist Alan Bishop of the Los Alamos National Laboratory in New Mexico has shown that the controlled stopping of such solitons may offer a convenient way to store information. They studied the equations that describe an optical soliton passing through a gas whose quantum properties are controlled by a laser beam, and explored what would happen if the control laser were suddenly turned off once the soliton had entered the gas. They showed that turning off the laser would trigger a shock wave at the point where the soliton first entered the gas, which would chase after the soliton and eventually catch up and stop it in its tracks ().
鈥淏y turning the laser off at a precise moment, it may be possible to write information on atoms at specific positions鈥�
While the soliton vanishes when it stops, its former presence is registered in the properties of atoms in the immediate vicinity, marking them out from the atoms elsewhere in the gas. So by turning the laser off at a precise moment, it is theoretically possible to write information onto atoms at specific locations.
鈥淭he information would last for about a thousandth of a second,鈥� says physicist Andrei Rybin of the University of Jyv盲skyl盲 in Finland, a member of the team. This is a long time for light, and could provide a way for quantum computers to store information during calculations.
