Quantum Backaction on Kg-Scale Mirrors: Observation of Radiation Pressure Noise in the Advanced Virgo Detector

The quantum radiation pressure and the quantum shot noise in laser-interferometric gravitational wave
detectors constitute a macroscopic manifestation of the Heisenberg inequality. If quantum shot noise can be
easily observed, the observation of quantum radiation pressure noise has been elusive, so far, due to the
technical noise competing with quantum effects. Here, we discuss the evidence of quantum radiation
pressure noise in the Advanced Virgo gravitational wave detector. In our experiment, we inject squeezed
vacuum states of light into the interferometer in order to manipulate the quantum backaction on the 42 kg
mirrors and observe the corresponding quantum noise driven displacement at frequencies between 30 and
70 Hz. The experimental data, obtained in various interferometer configurations, is tested against the
Advanced Virgo detector quantum noise model which confirmed the measured magnitude of quantum
radiation pressure noise.