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The ability to detect the magnetism from an individual electron is based on the exquisite sensitivity of an ultrathin silicon microcantilever like this one. Shaped like a miniature diving board, this cantilever is 85 micrometers long (roughly the diameter of a human hair) and the shaft is only 100 nanometers thick (some 1,000 times thinner than a human hair). Because the cantilever is so thin, it is extremely flexible and can detect ultrasmall forces in the attonewton range. In the experiments performed at IBM's Almaden Research Center, a tiny magnetic particle is attached to the cantilever tip so it can be used in a magnetic resonance force microscope (MRFM). The cantilever is vibrated at its natural frequency (5,000 cycles per second), and interaction with an electron spin changes the cantilever's vibration frequency by about 1 part per million. (The scale bar represents about 10 micrometers.)
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