Motion sensor nears quantum limit

Researchers from the University of California at Santa Barbara have constructed a device that can measure movements as small as one thousandth of a nanometer, which is one hundredth the size of a hydrogen atom.

To make the extremely sensitive device the researchers combined a single electron transistor and a nanomechanical beam, which is a microscopic, vibrating cantilever.

The single electron transistor, or SET, is very sensitive to electrical charge, and can detect a charge of one millionth of an electron. The researchers put the single electron transistor very close to the nanomechanical beam and put voltage through the resonator. The voltage made the beam vibrate, and the vibrations affected the way single electrons passed through the transistor. Displacement, or how much an object has moved, can be inferred from this measurement.

The famous Heisenberg uncertainty principle says that once you get down to a certain size, you cannot measure a particle's position and its velocity at the same time. In order to test the Heisenberg principle empirically the researchers' detector would have to be 100 times more sensitive.

The researchers are currently working on making a higher frequency resonator. The work appeared in the July 17, 2003 issue of Nature.