Improving the stability of frequency-dependent squeezing with bichromatic control of filter cavity length, alignment, and incident beam pointing

authored by
Yuhang Zhao, Eleonora Capocasa, Marc Eisenmann, Naoki Aritomi, Michael Page, Yuefan Guo, Eleonora Polini, Koji Arai, Yoichi Aso, Martin van Beuzekom, Yao-Chin Huang, Ray-Kuang Lee, Harald Lueck, Osamu Miyakawa, Pierre Prat, Ayaka Shoda, Matteo Tacca, Ryutaro Takahashi, Henning Vahlbruch, Marco Vardaro, Chien-Ming Wu, Matteo Leonardi, Matteo Barsuglia, Raffaele Flaminio

Frequency-dependent squeezing is the main upgrade for achieving broadband quantum noise reduction in upcoming observation runs of gravitational wave detectors. The proper frequency dependence of the squeezed quadrature is obtained by reflecting squeezed vacuum from a Fabry-Perot filter cavity detuned by half of its line width. However, since the squeezed vacuum contains no classical amplitude, copropagating auxiliary control beams are required to achieve the filter cavity's length, alignment, and incident beam pointing stability. In our frequency-dependent squeezing experiment at the National Astronomical Observatory of Japan, we used a control beam at a harmonic of squeezed vacuum wavelength and found visible detuning variation related to the suspended mirrors angular drift. These variations can degrade interferometer quantum noise reduction. We investigated various mechanisms that can cause the filter cavity detuning variation. The detuning drift is found to be mitigated sufficiently by fixing the incident beam pointing and applying filter cavity automatic alignment. It was also found that there is an optimal position of the beam on the filter cavity mirror that helps to reduce the detuning fluctuations. Here, we report a stabilized filter cavity detuning variation of less than 10 Hz compared to the 113 Hz cavity line width. Compared to previously published results [Phys. Rev. Lett. 124, 171101 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.171101, such detuning stability would be sufficient to make filter cavity detuning drift induced gravitational wave detector detection range fluctuation reduce from 11% to within 2%.

Institute of Gravitation Physics
External Organisation(s)
University of Tokyo
Astroparticle and Cosmology Laboratory, Paris
National Astronomical Observatory of Japan (NAOJ)
Universite de Savoie
National Institute for Subatomic Physics (Nikhef)
LIGO Laboratory
National Tsing Hua University
University of Amsterdam
University of Padova
Physical Review D
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Peer reviewed
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