| 研究課題/領域番号 |
20F20713
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| 研究機関 | 国立天文台 |
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研究代表者 |
麻生 洋一 国立天文台, 重力波プロジェクト, 准教授 (10568174)
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| 研究分担者 |
PAGE MICHAEL 国立天文台, 重力波プロジェクト, 外国人特別研究員
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| 研究期間 (年度) |
2020-11-13 – 2023-03-31
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| キーワード | 重力波 |
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| 研究実績の概要 |
This research is based around broadband quantum noise improvement of the gravitational wave detector KAGRA. Current gravitational wave detectors have managed improve quantum shot noise below the standard quantum limit at detection frequencies around 1 kHz. However, by Heisenberg Uncertainty this comes with an associated increase in quantum radiation pressure noise, which is prominent at low frequency. The reduction of noise in one quantum quadrature at the expense of increase in another is known as squeezing. For gravitational wave detector upgrades, the increase in radiation pressure noise becomes increasingly relevant with the suppression of low frequency fundamental and technical noises. Therefore, we desire that quantum noise is squeezed in a frequency dependent manner, where the transition between shot noise and radiation pressure squeezing occurs at approximately 50 Hz.
The TAMA300 optical cavity test facility located at the National Astronomical Observatory of Japan has previously been used to demonstrate squeezing in an environment applicable to gravitational wave detection, using large seismically isolated optics in vacuum. The latest measurement of frequency dependent squeezing showed that backscattered light greatly limited the degree of detectable squeezing. Some of the sources of backscatter in the squeezer’s control and detection optics were reduced, and the frequency independent squeezed field noise performance was improved. However, the filter cavity, which produces the required frequency dependence, still introduces considerable squeezing degradation.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The major limitations to frequency dependent squeezing are optical loss, as well as noise in the rotation of the squeezing quadrature, which we refer to as squeezing phase noise. Currently, we are investigating the sources of squeezing degradation that are present. Also, adding extra lasers and suspended optics to a gravitational wave detector will introduce scattered light, which can interfere with and degrade the small gravitational wave signal. While frequency dependent squeezing has been maintained with a quadrature transition of about 90 Hz, there is still considerable optical backscattering that limits the observable squeezing in TAMA at low frequency. Thus, we are working on investigating and reducing backscattering from both the squeezer and filter cavity. The optical parametric oscillator, a nonlinear optic used to generate squeezing, has been identified as the next target for optical loss and backscattering improvement with regards to the squeezer. For the filter cavity, the major point of investigation right now is to improve its automated alignment sensing and control to reduce backscatter from the suspended optics.
In addition to experimental work, NAOJ has recently established a working group in KAGRA to develop the frequency dependent squeezing module for the KAGRA detector. This research is in a preliminary state of literature review and initial design studies. KAGRA-specific global design parameters for the new filter cavity must be decided before a specific plan and noise budget can be produced.
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| 今後の研究の推進方策 |
The next task for achieving frequency dependent squeezing in the KAGRA detector will be to integrate the filter cavity setup into the detector. A working group has been established with other researchers in the KAGRA collaboration. Under this program, I will take particular responsibility for the design of the filter cavity control system. If length fluctuations of the filter cavity are not sufficiently suppressed, then the correct frequency dependence of the squeezing angle cannot be maintained, greatly increasing quantum noise.
Control of the filter cavity length with respect to the squeezed vacuum field is not straightforward, since there is no amplitude contained in the quantum vacuum fluctuations. Thus, additional control fields must be set up, detuned from the squeezed field and co-propagating throughout the optical system. Prototype control schemes have been developed at LIGO, GEO600 and TAMA but none of these have interfaced squeezed vacuum with a gravitational wave detector. Interfacing the filter cavity with the detector adds the additional challenge of properly mode matching and aligning the control fields to the interferometer, as well as ensuring sufficient suppression of stray light from the control fields and squeezing optics. We will undertake a detailed calculation of the noise budget of potential frequency dependent squeezing control schemes for the specific case of the KAGRA detector. It will also be useful to check mutual compatibility of the control schemes with each other and develop an appropriate hierarchy of use cases.
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