A sensor the size of a rice grain can detect magnetic fields as small as those produced by brain waves, researchers report.
John Kitching of the National Institute of Standards and Technology in Boulder, Colo., and his colleagues filled a millimeterwide silicon cylinder, sealed by glass at both ends, with a gas of about 100 billion rubidium atoms. Under normal conditions, shining a laser through the container causes the spins of the atoms to line up.