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Electronics giant Fujitsu says it has succeeded in making an experimental
quantum dot memory device that can store data on an atomic scale. Each
20-nanometre-diameter quantum dot cell is made of indium arsenide surrounded by
gallium arsenide. When light from a laser is shone on a cell, electron-hole
pairs are generated. Light from a different laser is then shone on the cell to
detect the presence or absence of electrons, corresponding to two binary states
(see “Take one quantum dot . . .”, ¿ìè¶ÌÊÓƵ, 29 August 1998, p
22). Researchers at Fujitsu’s labs in Atsugi say the device packs large amounts
of data into a small space: it’s just 500 micrometres in diameter and about 80
nanometres in height and holds more than half a billion stacked quantum
dots.