Pierre-François Cohadon (Laboratoire Kastler Brossel and Virgo Collaboration)

Gravitational-wave detection and quantum-limited measurements

Detecting gravitational waves required 4 decades of experimental effort to reach a sensitivity at the h~10-21 level, corresponding to mirror displacements below 10-18 m.

I will  review this "noise hunting" effort and give some details about the recent observation of 2 neutron star mergers.

Apart from classical noise (seismic noise, thermal noise...), it was realized as soon as in the late 70s that quantum fluctuations of the light field were responsible for the Standard Quantum Limit, a sensitivity limit that second-generation gravitational-wave interferometers will reach once they operate at their design sensitivity, within a few years. A number of ideas have been considered to beat the SQL: squeezed states of the light field, tailoring the optical response function or taking advantage of the mirror mechanical response to radiation pressure. I will present the first experimental demonstrations of such ideas, either on suspended interferometers or table-top experiments.