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Free keywords:
General Relativity and Quantum Cosmology, gr-qc,Quantum Physics, quant-ph
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 $\gamma_{1,2}$
and of the optical circulating power $I_{1,2}$, with the special relationship
of $I_1/I_2=\gamma_1/\gamma_2$. 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 gravitational-wave 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 $\sim 30\,{\rm Hz}$ 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.
