Frictionless Bearing for the Measurement of
the Quantum Electrodynamical Torque
Davide Iannuzzi, Jeremy N. Munday, Y. Barash, and Federico Capasso
We have calculated that quantum fluctuations of the electromagnetic field should induce on a micromachined calcite (or quartz) disk kept parallel to a barium titanate plate, a torque of ~10-19 Nm. This torque should be measurable by immersing the two slabs in liquid ethanol. In this case, the Casimir force between them is known from theory to be repulsive. The disk should float on top of the plate at a distance where its weight is counterbalanced by the Casimir force. The static friction between the slabs should be virtually zero, and the disk should be free to rotate suspended in close proximity (~100 nm) with the plate. In the experiment a polarized laser beam is used to impart a torque to the disk and is then blocked; the disk under the action of the QED torque will return to a configuration of optical axis aligned to that of the plate, corresponding to zero torque. The inset shows the calculated angular position as a function of time after the laser has been blocked. Note that calcite and quartz experience torques of opposite sign.