We have performed an experiment in order to measure the displacement of a mirror at the attometer level. The mirror is coated on a high-Q millimeter-sized mechanical resonator made of fused silica. Using a high-finesse optical cavity, a highly stabilized Ti:Sa laser source and a low-noise detection system allows us to reach a shot-noise limited sensitivity of 2.8 10-19 m/√Hz at the resonator’s fundamental acoustic resonance frequency, about 2 MHz. We have also implemented a feedback scheme, where the information about the mirror's motion is used in a feedback loop to control the intensity of a radiation pressure force applied onto the mirror. This allows to reduce the thermal noise and to cool down the mirror well below its initial temperature. The effect of this cold damping mechanism is visualized both on the temporal evolution of the mirror displacement and on its distribution in phase-space, with a sensitivity of a few attometers.
We have also observed the thermal noise squeezing in the case of a parametrically-modulated feedback force, observing both the 50% theoretical limit of squeezing below the mirror’s parametric oscillation threshold, and the oscillation above threshold. Enhancement of the experimental setup, with the use of an optical cavity with a higher finesse inserted in a liquid helium cryostat, in order to observe quantum effects of radiation pressure such as the Standard Quantum Limit, will also be discussed.