After 2 1/2 years of experimenting with a room full of lasers and vacuum chambers, California Institute of Technology researchers say they have built a microscope that shows the motion of a single atom. "On the second day we ran it, we saw these wiggly signals, and we said: `Wow, those look like trapped atoms,"' says Christina J. Hood, one of the scientists.

The atom-cavity microscope, as it is called, uses single particles of light to trap atoms. A photon is confined in a cavity about 10 microns wide (four ten-thousandths of an inch). The cavity resonates at a certain frequency of light, just as a half-filled bottle produces a particular note when air is blown across it. The photon bounces back and forth, building up an electric field that can capture an atom--in this case, cesium. When the cesium atom moves, it changes the frequency (like adding water to the bottle), and that allows researchers to track the atom's motion.

Hood and her colleagues, including Caltech physics professor H. Jeff Kimble, reported their findings in the Feb. 25 issue of Science. They say the microscope will aid the development of quantum computers and help researchers understand fundamental reactions by allowing them to watch how single atoms and molecules interact.

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