Amplifying quantum signals with the single-electron transistor

Transistors have continuously reduced in size and increased in switching sp eed since their invention in 1947. The exponential pace of transistor evolu tion has led to a revolution in information acquisition, processing and com munication technologies. And reigning over most digital applications is a s ingle device structure - the field-effect transistor (FET). But as device d imensions approach the nanometre scale, quantum effects become increasingly important for device operation, and conceptually new transistor structures may need to be adopted. A notable example of such a structure is the singl e-electron transistor, or SET1-4. Although it is unlikely that SETs will re place FETs in conventional electronics, they should prove useful in ultra-l ow-noise analog applications. Moreover, because it is not affected by the s ame technological limitations as the FET, the SET can approach closely the quantum limit of sensitivity. It might also be a useful read-out device for a solid-state quantum computer.