Keeping Time with Light
An international team of researchers based at the universities of Vienna, Duisburg-Essen and Tel Aviv have succeeded in using polarized laser light to rotate a nanorod in a controlled fashion, providing a stable micromechanical oscillator for an electronic timekeeper. With the aid of laser beams, the group led by Stefan Kuhn, James Millen and Markus Arndt of the University of Vienna trapped a silicon nanorad, less than one-thousandth of a millimeter long, in a vacuum. The two counter-propagating light beams effectively keep the rod in suspension, and a third laser is used to rotate the rod by means of pulses of polarized light. Since the rotation is locked to the pulse frequency, the rotation period is sufficiently stable to act as a high-precision clock. Over a period of 4 days, this clock loses no more than a millionth of a second.