Quantum-nondemolition measurement of light by a piezoelectric crystal

Abstract
We show that an optical cavity made of mirrors coated on a piezoelectric crystal can provide a quantum-nondemolition measurement of the intensity of a light beam. Due to radiation pressure, the crystal length is sensitive to the light intensity and can be measured by an electric circuit. The intensity fluctuations are not modified by reflection on such a cavity and the quantum correlations between these fluctuations and the output current of the electric circuit can be made very large even at nonzero temperature.