A scheme to probe optomechanical correlations between two optical beams down to the quantum level

Quantum effects of radiation pressure are expected to limit the sensitivity of second-generation gravitational-wave interferometers. Using a high-finesse optical cavity and a classical intensity noise, radiation-pressure induced correlations between two optical beams sent into the same moving mirror cavity is demonstrated. The intensity fluctuations of the first, high-power, signal beam are imprinted onto the mirror motion by radiation pressure, whereas the resulting position fluctuations are monitored through the phase of the second, weaker, meter beam. As the intensity fluctuations of the signal beam are unchanged by reflection upon the cavity, the intensity-phase correlations observable between the two reflected beams provide a direct measurement of the optomechanical correlations.