Speedmeter scheme for gravitational-wave detectors based on EPR quantum entanglement

Abstract

We propose a new implementation of a quantum speed meter QND measurement scheme. It employs two independent optical readouts of the interferometer test masses, featuring strongly different values of the bandwidths γ 1,2 and of the optical circulating power I 1,2 , with the special relationship of I 1 /I 2 = γ 1 /γ 2 . The outputs of these two position meters have to be combined by an additional beamsplitter. In this scheme, signals at the common and the differential outputs of the interferometer setup are proportional to the position and the velocity of the test masses, respectively. The influence of the position meter-like back action force associated with the position signal can be cancelled using the EPR approach by measuring the amplitude quadrature of the beamsplitter common output correlated with this force. In the standard signal-recycled Michelson interferometer topology of the modern gravitationalwave detectors, two independent optical position meters can be implemented by two orthogonal polarisations of the probe light. Our analysis shows that the EPR speedmeter provides significantly improved sensitivity for all frequencies below ∼ 30 Hz compared to an equivalent signal recycled Michelson interferometer. We believe the EPR speedmeter scheme to be very attractive for future upgrades of gravitational wave detectors, because it requires only minor changes to be implemented in the interferometer hardware and allows to switch between the position meter and the speed meter modes within short time-scales and without any changes to the hardware.

A cryogenic silicon interferometer for gravitational-wave detection

“…The main approach relevant to LIGO Voyager is squeezed light injection. Work has also been done on alternative interferometer optical topologies to recycled Michelson interferometers [68], but these are not discussed here. Squeezing is a well-tested technology and was demonstrated in GEO600 and in the H1 LIGO interferometer [69,70,71], in preparation for use in the second generation detectors like Advanced LIGO and Advanced Virgo.…”

A Cryogenic Silicon Interferometer for Gravitational-wave Detection

“…The main approach relevant to LIGO Voyager is squeezed light injection. Work has also been done on alternative interferometer optical topologies to recycled Michelson interferometers [60], but these are not discussed here. Squeezing is a well-tested technology and was demonstrated in GEO600 and in the H1 LIGO interferometer [61,62,63], in preparation for use in the second generation detectors like Advanced LIGO and Advanced Virgo.…”

Advanced quantum techniques for future gravitational-wave detectors

“…In 2017, Knyazev et al [78] proposed a third distinct way to realise speed measurement in GW laser interferometer, using 2 position meters (Fabry-Pérot-Michelson interferometers, see Fig. 24a that have rigidly connected test masses (or simply share them) but have contrasting light storage times (bandwidths satisfy condition γ 1 γ 2 ).…”

“…As the design of Fig. 24a is obviously a nightmare to implement in a real GW detector (it was never intended to be), another one, based on orthogonal polarisation modes of light was proposed in [78] and is shown in Fig. 24b.…”

“…Sec. 2.1 and the Appendix of [78]). Quantum correlations between the two readouts are at its strongest at the lower frequencies, where both MIs output light fields,b b b (1) andb b b (2) , are strongly squeezed due to ponderomotive squeezing discussed in Sec.…”