Light writes data in electrons

Many research teams are working on spintronics -- controlling the spin of electrons so they can be used to represent information. Electrons have two possible spin directions, somewhat like a top that can spin clockwise or counterclockwise.

These spin directions can be used to represent the 1s and 0s of computer information in standard classical computers. Single electron spins can also be used as quantum bits, the basic logic unit of quantum computers. Quantum computers have the potential to solve certain types of problems many orders of magnitude faster than classical computers.

Key to using spin to represent information is being able to set electron spin, store the electrons, and read the electrons' spins.

Researchers at the Technical University of Munich in Germany have advanced the field with an optically programmable spin memory device that writes data as electron spins using lasers, stores the electrons in bits of semiconductor dubbed quantum dots, and reads spin information by applying a voltage to the quantum dots to convert the electrons to photons.

The researchers have shown that it is possible to store spins in their device for longer than 20 milliseconds, which is enough time to carry out computations on the information.

The researchers' prototype of gallium indium arsenide quantum dots works in a magnetic field of 4 tesla and a temperature near absolute zero. A tesla is about 10 times the strength of a kitchen magnet.

Because the spins are programmed optically, many spin systems can be programmed at once, according to the researchers. The researchers are working on ways to measure individual spins separately.

The optically-programmed spin method could be used practically in classical computers in five to ten years, according to the researchers. Most researchers agree that quantum computers will not be practical for one or two decades. The work appeared in the November 4, 2004 issue of Nature.