arXiv:1806.10506 · Physical review. D/Physical review. D.
Measurement of optical losses in a high-finesse 300 m filter cavity for broadband quantum noise reduction in gravitational-wave detectors
E. Capocasa, Yuefan Guo, M. Eisenmann, Yang Zhao, Akihiro Tomura, Koji Arai, Y. Aso, M. Marchio, Laurent Pinard, Pierre Prat, Kentaro Somiya, R. Schnabel, Matteo Tacca, Ryutaro Takahashi, Daisuke Tatsumi, M. Leonardi, M. Barsuglia, Raffaele Flaminio
Earth-based gravitational-wave detectors will be limited by quantum noise in a large part of their spectrum. The most promising technique to achieve a broadband reduction of such noise is the injection of a frequency-dependent squeezed vacuum state from the output port of the detector, with the squeeze angle rotated by the reflection off a Fabry-Perot filter cavity. One of the most important parameters limiting the squeezing performance is represented by the optical losses of the filter cavity. We report here the operation of a 300 m filter cavity prototype installed at the National Astronomical Observatory of Japan. The cavity is designed to obtain a rotation of the squeeze angle below 100 Hz. After achieving the resonance of the cavity with a multiwavelength technique, the round trip losses have been measured to be between 50 and 90 ppm. This result demonstrates that with realistic assumptions on the input squeeze factor and the other optical losses, a quantum noise reduction of at least 4 dB in the frequency region dominated by radiation pressure can be achieved.
Earth-based gravitational-wave detectors will be limited by quantum noise in a large part of their spectrum. The most promising technique to achieve a broadband reduction of such noise is the injection of a frequency-dependent squeezed vacuum state from the output port of the detector, with the squeeze angle rotated by the reflection off a Fabry-Perot filter cavity. One of the most important parameters limiting the squeezing performance is represented by the optical losses of the filter cavity. We report here the operation of a 300 m filter cavity prototype installed at the National Astronomical Observatory of Japan. The cavity is designed to obtain a rotation of the squeeze angle below 100 Hz. After achieving the resonance of the cavity with a multiwavelength technique, the round trip losses have been measured to be between 50 and 90 ppm. This result demonstrates that with realistic assumptions on the input squeeze factor and the other optical losses, a quantum noise reduction of at least 4 dB in the frequency region dominated by radiation pressure can be achieved.
The sensitivity of the gravitational-wave detector KAGRA, presently under construction, will be limited by quantum noise in a large fraction of its spectrum. The most promising technique to increase the detector sensitivity is the injection of squeezed states of light, where the squeezing angle is dynamically rotated by a Fabry-P\'erot filter cavity. One of the main issues in the filter cavity design and realization is the optical losses due to the mirror surface imperfections. In this work we present a study of the specifications for the mirrors to be used in a 300 m filter cavity for the KAGRA detector. A prototype of the cavity will be constructed at the National Astronomical Observatory of Japan, inside the infrastructure of the former TAMA interferometer. We also discuss the potential improvement of the KAGRA sensitivity, based on a model of various realistic sources of losses and their influence on the squeezing amplitude.
Abstract Quantum noise is limiting the sensitivity of ground based gravitational wave detectors both at high frequency, in the form of shot noise, and low frequency, in the form of radiation pressure noise. In the last observing run, the injection of frequency independent squeezing improved Virgo and LIGO sensitivities at high frequency, slightly worsening the performance at low frequency. A broadband quantum noise reduction can be achieved using frequency dependent squeezing, i. e. rotating the vacuum squeezed ellipse below 100 Hz by reflecting the squeezed vacuum off a Fabry–Perot cavity, called filter cavity. The frequency-dependent squeezed quadrature rotation with rotation frequency around a few tens of Hz has been proven at National Astronomical Observatory of Japan (NAOJ) and at Massachusetts Institute of Technology (MIT). The experiment at NAOJ uses the former TAMA facility, a 300 meter long filter cavity, reproducing in scale the ones planned to be installed in Virgo and LIGO. Once the frequency dependent squeezing is produced, it has to be injected into the interferometer. This interface is not trivial, since it requires the installation of additional benches and a 285 meter long cavity (in Advanced Virgo Plus) and also to couple the rotating squeezed vacuum with the detector. An important issue which can worsen the performance of frequency dependent squeezing or directly the interferometer sensitivity is the stray light. To avoid the propagation of additional stray light, we traced the ghost beam on squeezing benches, inside linking tubes and inside the filter cavity and several diaphragms and baffles will be installed to limit this problem.
The astrophysical reach of current and future ground-based gravitational-wave detectors is mostly limited by quantum noise, induced by vacuum fluctuations entering the detector output port. The replacement of this ordinary vacuum field with a squeezed vacuum field has proven to be an effective strategy to mitigate such quantum noise and it is currently used in advanced detectors. However, current squeezing cannot improve the noise across the whole spectrum because of the Heisenberg uncertainty principle: when shot noise at high frequencies is reduced, radiation pressure at low frequencies is increased. A broadband quantum noise reduction is possible by using a more complex squeezing source, obtained by reflecting the squeezed vacuum off a Fabry-Perot cavity, known as filter cavity. Here we report the first demonstration of a frequency-dependent squeezed vacuum source able to reduce quantum noise of advanced gravitational-wave detectors in their whole observation bandwidth. The experiment uses a suspended 300-m-long filter cavity, similar to the one planned for KAGRA, Advanced Virgo, and Advanced LIGO, and capable of inducing a rotation of the squeezing ellipse below 100 Hz.
In this Letter, we present the design and performance of the frequency-dependent squeezed vacuum source that will be used for the broadband quantum noise reduction of the Advanced Virgo Plus gravitational-wave detector in the upcoming observation run. The frequency-dependent squeezed field is generated by a phase rotation of a frequency-independent squeezed state through a 285 m long, high-finesse, near-detuned optical resonator. With about 8.5 dB of generated squeezing, up to 5.6 dB of quantum noise suppression has been measured at high frequency while close to the filter cavity resonance frequency, the intracavity losses limit this value to about 2 dB. Frequency-dependent squeezing is produced with a rotation frequency stability of about 6 Hz rms, which is maintained over the long term. The achieved results fulfill the frequency dependent squeezed vacuum source requirements for Advanced Virgo Plus. With the current squeezing source, considering also the estimated squeezing degradation induced by the interferometer, we expect a reduction of the quantum shot noise and radiation pressure noise of up to 4.5 dB and 2 dB, respectively.
The current generation of gravitational wave laser interferometer detectors operate at the sensitivity limit imposed by quantum uncertainty of photon amplitude and phase quadratures. Heisenberg's principle dictates that the product of amplitude and phase uncertainty must be above a certain value, but apart from that we can still manipulate either quadrature to achieve quantum noise reduction, since the effect of amplitude and phase uncertainty is frequency dependent in gravitational wave detectors. This is the crux of the frequency dependent squeezing technique, which reduces quantum amplitude uncertainty at low frequency and quantum phase uncertainty at high frequency, where these respective quadratures each dominate. Thus, we can reduce quantum noise across the entire detection band. However, this technique is extremely sensitive to optical losses at all parts of the squeezing generation chain, and so far only a low degree of broadband squeezing has been observed. This proceeding outlines the current status of squeezing research at the former TAMA300 gravitational wave detector at the National Astronomical Observatory of Japan, where we aim to improve the level of achievable broadband squeezing. An update is also given regarding design and noise of squeezed injection for the underground gravitational wave detector KAGRA located in Gifu, Japan.
The first detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 launched the era of gravitational-wave astronomy. The quest for gravitational-wave signals from objects that are fainter or farther away impels technological advances to realize ever more sensitive detectors. Since 2019, one advanced technique, the injection of squeezed states of light, is being used to improve the shot-noise limit to the sensitivity of the Advanced LIGO detectors, at frequencies above ∼50 Hz. Below this frequency, quantum backaction, in the form of radiation pressure induced motion of the mirrors, degrades the sensitivity. To simultaneously reduce shot noise at high frequencies and quantum radiation pressure noise at low frequencies requires a quantum noise filter cavity with low optical losses to rotate the squeezed quadrature as a function of frequency. We report on the observation of frequency-dependent squeezed quadrature rotation with rotation frequency of 30 Hz, using a 16-m-long filter cavity. A novel control scheme is developed for this frequency-dependent squeezed vacuum source, and the results presented here demonstrate that a low-loss filter cavity can achieve the squeezed quadrature rotation necessary for the next planned upgrade to Advanced LIGO, known as "A+."