Ultra-sensitive measurement of thermal and quantum noises

We have developed an experiment of ultrasensitive interferometric measurement of small displacements based on a high-finesse Fabry-Perot cavity. We have observed the internal thermal noise of mirrors and fully characterized their acoustics modes. We describe recent progress in our experimental setup in order to reach a sensitivity better than 10−20m/√Hz. This unique sensitivity is a step towards the first observation of the radiation pressure effects and the resulting standard quantum limit in interferometric measurements. Our experiment may become a powerful facility to test quantum noise reduction schemes such as the use of squeezed light or quantum locking of mirrors. We also present a new scheme where a cavity detuning changes the mirror dynamics in such a way that the gravitational signal is amplified by the optomechanical coupling and the interferometer sensitivity is improved.