EPR experiment for a broadband quantum noise reduction in gravitational wave detectors

Squeezed states of light contribute to the reduction of quantum noise in gravitational-wave interferometers. This result, predicted by Caves in 1981, has been demonstrated by the main gravitational-wave detectors. The injection of phase-squeezed light only decreases quantum shot noise fluctuations, improving the detector sensitivity in high-frequency band; the corresponding anti-squeezing, indeed, induces radiation pressure noise, increasing quantum noise in low-frequency band. This becomes important for near detector generation, where current low frequency noises, that cover the radiation pressure noise, will be reduced. To face this problem, the use of frequency dependent squeezing, obtained using a long external filter cavity, is planned. An alternative method,
based on EPR experiment, can be used for the same purpose. It has the advantage to avoid further complex infrastructures required for the filter cavity. We propose a table-top experiment to test the broadband quantum noise reduction that can be obtained injecting entangled beams through the interferometer dark port. The conceptual design and the possible implementation in a small-scale suspended interferometer will be presented.