A new quantum speed-meter interferometer: measuring speed to search for intermediate mass black holes

The recent discovery of gravitational waves (GW) by Advanced LIGO (Laser Interferometric Gravitational-wave Observatory) has impressively launched the novel field of gravitational astronomy and allowed us to glimpse exciting objects about which we could previously only speculate. Further sensitivity improvements at the low-frequency end of the detection band of future GW observatories must rely on quantum non-demolition (QND) methods to suppress fundamental quantum fluctuations of the light fields used to readout the GW signal. Here we present a novel concept of how to turn a conventional Michelson interferometer into a QND speed-meter interferometer with coherently suppressed quantum back-action noise. We use two orthogonal polarizations of light and an optical circulator to couple them. We carry out a detailed analysis of how imperfections and optical loss influence the achievable sensitivity. We find that the proposed configuration significantly enhances the low-frequency sensitivity and increases the observable event rate of binary black-hole coalescences in the range of 1 0 2 - 1 0 3 M ⊙ by a factor of up to ~300. Gravitational wave detection: Improved Sensitivity A new design of interferometric gravitational wave detector proposed by scientists from Russia, Germany and the UK could potentially boost the detection rate of intermediate black hole events by a factor of several hundred. Analysis indicates that the team’s “polarization circulation speed meter” interferometer design has significantly better noise performance at low frequencies (1-100 Hz) than traditional Fabry-Perot Michelson interferometers. The improvement is due to coherent suppression of quantum back-action noise and the use of two orthogonal polarizations of light. A critical factor in the performance of the design is the optical loss of the quarter wave plate used to separate the two polarizations of light and this needs to be kept as low as possible. The team is now investigating the benefit of using squeezed light states with the scheme for further sensitivity improvements.