TITomohiro Ishikawa

Tomohiro Ishikawa

Nagoya University
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Tomohiro Ishikawa has a total of 78 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    Ground-based gravitational wave detector using rapidly repeated free-falling test masses

    by Shoki Iwaguchi, Bin Wu, Kurumi Umemura, Tomohiro Ishikawa, Kenji Tsuji, Ryota Nishimura, Yuta Michimura, Yutaro Enomoto, Soichiro Morisaki, Yoichi Aso, et al.

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    Proof-of-principle experiment on a displacement-noise-free neutron interferometer for gravitational wave detection

    by Shoki Iwaguchi, Takuhiro Fujiie, Taro Nambu, Masaaki Kitaguchi, Yutaka Yamagata, Kenji Mishima, Atsushi Nishizawa, Tomohiro Ishikawa, Kenji Tsuji, Kurumi Umemura, et al.

    The displacement-noise-free interferometer (DFI) is designed to eliminate all displacement-induced noise while retaining sensitivity to gravitational wave (GW) signals. Ground-based DFIs suffer from physical arm-length limitations, resulting in poor sensitivity at frequencies below 1 kHz. To address this, previous research introduced a neutron-based DFI, which replaces laser light with neutrons and achieves exceptional sensitivity down to a few hertz. In this study, we conducted a proof-of-principle experiment using a pulsed neutron source at the Japan Proton Accelerator Research Complex. Despite practical constraints that led to deviations from the ideal experimental design, we optimized the setup and developed a novel analysis method that successfully cancels displacement noise while preserving simulated GW signals. This work presents the first successful demonstration of a neutron DFI and a neutron interferometer for GW detection.

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    Feasibility of loop-gain tuning for general measurement systems inspired by quantum locking for DECIGO

    by T Ishikawa, Y Kawasaki, K Tsuji, R Shimizu, K Umemura, B Wu, S Iwaguchi, Y Michimura, K Nagano, Y Enomoto, et al.

    A series of quantum locking theories have been proposed to enhance the quantum-noise-limited target sensitivity of the DECi-hertz Interferometer Gravitational wave Observatory. The quantum locking that uses a square completion optimizes the sensitivity across all frequencies. However, a substantial amount of data-series must be post-processed since the square completion is a form of signal processing technique. This paper approaches the optimal sensitivity across all frequencies from an alternative perspective: by optimizing the frequency dependence of a servo gain in a feedback loop. The optimal servo gain is formulated by comparing the alternative method with the square completion method for the same optical setup. This will be shown in general noise issues extending the framework of the quantum locking. We find that the optimal servo gain forms a non-feasible filter but has certain characteristics. We also find that the noise of the measurement signal deteriorates proportionally to the noise measured in the feedback loop when the servo gain is slightly imperfect.

    Cited by 1
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    Sagnac-type neutron displacement-noise-free interferometeric gravitational-wave detector

    by Yuki Kawasaki, Shoki Iwaguchi, Tomohiro Ishikawa, Atsushi Nishizawa, Masaaki Kitaguchi, Yutaka Yamagata, Yanbei Chen, Bin Wu, Ryuma Shimizu, Kurumi Umemura, et al.

    The detection of low-frequency gravitational waves on Earth requires the reduction of displacement noise, which dominates the low-frequency band. One method to cancel test mass displacement noise is a neutron displacement-noise-free interferometer (DFI). This paper proposes a new neutron DFI configuration, a Sagnac-type neutron DFI, which uses a Sagnac interferometer in place of the Mach–Zehnder interferometer. We demonstrate that a sensitivity of the Sagnac-type neutron DFI is higher than that of a conventional neutron DFI with the same interferometer scale. This configuration is particularly significant for neutron DFIs with limited space for construction and limited flux from available neutron sources.

    Cited by 2
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    Significance of Fabry-Perot Cavities for Space Gravitational Wave Antenna DECIGO

    by Kenji Tsuji, Tomohiro Ishikawa, Kurumi Umemura, Yuki Kawasaki, Shoki Iwaguchi, Ryuma Shimizu, Masaki Ando, Seiji Kawamura

    DECIGO is a future Japanese project for the detection of gravitational waves in space. To conduct various scientific missions, including the verification of cosmic inflation through the detection of primordial gravitational waves as the main objective, DECIGO is designed to have high sensitivity in the frequency band from 0.1 to 10 Hz, with arms of length 1000 km. Furthermore, the use of the Fabry-Perotcavity in these arms has been established for the DECIGO project. In this paper, we scrutinize the significance of the Fabry-Perot cavity for promoting this project, with a focus on the possibility of observing gravitational waves from cosmic inflation and binary compact star systems as indicators. The results show that using the Fabry-Perot cavity is extremely beneficial for detecting them, and it is anticipated to enable the opening of a new window in gravitational wave astronomy.

    Cited by 5
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    Optimization of Quantum Noise in Space Gravitational-Wave Antenna DECIGO with Optical-Spring Quantum Locking Considering Mixture of Vacuum Fluctuations in Homodyne Detection

    by Kenji Tsuji, Tomohiro Ishikawa, Kentaro Komori, Koji Nagano, Yutaro Enomoto, Yuta Michimura, Kurumi Umemura, Ryuma Shimizu, Bin Wu, Shoki Iwaguchi, et al.

    Quantum locking using optical spring and homodyne detection has been devised to reduce the quantum noise that limits the sensitivity of the DECIGO, a space-based gravitational-wave antenna in the frequency band around 0.1 Hz for the detection of primordial gravitational waves. The reduction in the upper limit of energy density ΩGW from 2×10−15 to 1×10−16, as inferred from recent observations, necessitates improved sensitivity in the DECIGO to meet its primary science goals. To accurately evaluate the effectiveness of this method, this paper considers a detection mechanism that takes into account the influence of vacuum fluctuations on homodyne detection. In addition, an advanced signal processing method is devised to efficiently utilize signals from each photodetector, and design parameters for this configuration are optimized for the quantum noise. Our results show that this method is effective in reducing quantum noise, despite the detrimental impact of vacuum fluctuations on its sensitivity.

    Cited by 6
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    First-step experiment for sensitivity improvement of DECIGO: Sensitivity optimization for simulated quantum noise by completing the square

    by Tomohiro Ishikawa, Yuki Kawasaki, Kenji Tsuji, Rika Yamada, Izumi Watanabe, Bin Wu, Shoki Iwaguchi, Ryuma Shimizu, Kurumi Umemura, Koji Nagano, et al.

    Decihertz Interferometer Gravitational Wave Observatory (DECIGO) is a future mission for a space-borne laser interferometer. DECIGO has 1000-km-long arm cavities mainly to detect the primordial gravitational waves (PGWs) at lower frequencies around 0.1 Hz. Observations in the electromagnetic spectrum have lowered the bounds on the upper limit of PGWs energy density (Ωgw∼10−15→10−16). As a result, DECIGO’s target sensitivity, which is mainly limited by quantum noise, needs further improvement. To maximize the feasibility of detection while constrained by DECIGO’s large diffraction loss, a quantum locking technique with an optical spring was theoretically proposed to improve the signal-to-noise ratio of the PGWs. In this paper, we experimentally verify one key element used in the theory: sensitivity optimization by completing the square of multiple detector outputs. This experiment is operated on a simplified tabletop optical setup with classical noise simulating quantum noise. We succeed in getting the best of the sensitivities with two different laser powers by the square completion method.

    Cited by 9
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    Displacement-noise-free interferometeric gravitational-wave detector using unidirectional neutrons with four speeds

    by Shoki Iwaguchi, Atsushi Nishizawa, Yanbei Chen, Yuki Kawasaki, Tomohiro Ishikawa, Masaaki Kitaguchi, Yutaka Yamagata, Bin Wu, Ryuma Shimizu, Kurumi Umemura, et al.

    Cited by 6
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    Can the phase of radiation pressure fluctuations be flipped in a single path for laser interferometric gravitational wave detectors?

    by Tomohiro Ishikawa, Shoki Iwaguchi, Bin Wu, Izumi Watanabe, Yuki Kawasaki, Ryuma Shimizu, Yutaro Enomoto, Yuta Michimura, Akira Furusawa, Seiji Kawamura

    Cited by 1
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    Conceptual design and science cases of a juggled interferometer for gravitational wave detection

    by Bin Wu, Tomohiro Ishikawa, Shoki Iwaguchi, Ryuma Shimizu, Izumi Watanabe, Yuki Kawasaki, Yuta Michimura, Shuichiro Yokoyama, Seiji Kawamura

    The juggled interferometer (JIFO) is an Earth-based gravitational wave detector using repeatedly free-falling test masses. With no worries of seismic noise and suspension thermal noise, the JIFO can have much better sensitivity at lower frequencies than the current Earth-based gravitational wave detectors. The data readout method of a JIFO could be challenging if one adopts the fringe-locking method. We present a phase reconstruction method in this paper by building up a complex function which has a fringe-independent signal-to-noise ratio. Considering the displacement noise budget of the Einstein Telescope (ET), we show that the juggled test masses significantly improve the sensitivity at 0.1–2.5 Hz even with discontinuous data. The science cases brought with the improved sensitivity would include detecting quasinormal modes of black holes with 104–105  M⊙, testing Brans-Dicke theory with black-hole and neutron-star inspirals, and detecting primordial-black-hole-related gravitational waves.

    Cited by 5
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