arXiv subjects

Yuta Michimura

Publications and source records attributed to Yuta Michimura.

At least 19 recordsLinked to original sources

arXiv2026

Evaluating KAGRA upgrade scenarios for multimessenger observations of binary neutron stars

Binary neutron star mergers are key targets for multimessenger astronomy, motivating future upgrades of gravitational-wave detectors. For KAGRA, both broadband sensitivity improvements that increase the binary neutron star detection range, and high-frequency optimizations targeting neutron-star physics are under consideration. We present a computationally efficient framework to evaluate the multimessenger performance of detector upgrades by combining Fisher-matrix estimates of localization area and localization volume with detector duty factors and binary neutron star merger rates. We apply this framework to proposed KAGRA upgrade scenarios within the LIGO-Virgo-KAGRA network. For identical sources, the high-frequency upgrade improves sky localization by about 20% compared with the broadband option. However, when detection rates are taken into account, the broadband upgrade yields a larger number of well-localized events. Despite its shorter binary neutron star range than the other detectors, the inclusion of KAGRA increases the number of events localized within $10^3$ Mpc$^3$ volume by about 60%. These results provide a quantitative framework for evaluating future detector upgrades from the perspective of multimessenger observations.

gr-qc↗

arXiv2026

A Polarization-Decomposed Method for Simulating Inhomogeneous Birefringence in Laser-Interferometric Gravitational-Wave Detectors

Birefringence in test mass substrates is an emerging limitation for current and future laser-interferometric gravitational-wave detectors, particularly as detectors move toward higher circulating power, cryogenic operation, and crystalline optical materials. Spatially varying birefringence alters both the polarization state and spatial mode content of the intracavity field, reducing interference contrast and coupling into length and alignment control signals. Accurate modeling of these effects is complicated by the fact that most frequency-domain simulation tools employ scalar modal propagation and lack native support for polarization and two-dimensional substrate maps. In this work, we present a practical and general method for simulating inhomogeneous birefringence without modifying existing simulation frameworks. The approach represents the two polarization components as independent scalar fields and introduces their coupling through an equivalent triple-Mach-Zehnder construction that reproduces the Jones matrix of a birefringent medium. We demonstrate the method using realistic birefringence maps of the KAGRA sapphire input test masses. The technique is compatible with any frequency-domain interferometer model and enables efficient birefringence studies for next-generation gravitational-wave detectors.

physics.ins-det↗

arXiv2025

In situ substrate birefringence characterization in gravitational wave detectors using a heterodyne polarimetry method

High-quality test mass substrates play essential roles in laser interferometric gravitational wave detectors. Inhomogeneous birefringence distribution in test mass substrates, however, can degrade the sensitivity of the detector by introducing the optical loss and disturbing the interferometer controls. In this paper, we present a heterodyne polarimetry method that enables in situ birefringence characterizations, hence diagnosing the gravitational wave interferometer. We experimentally demonstrate the proposed method with a tabletop setup. We also discuss its applicability to current and future gravitational wave detectors and the detectable limit.

physics.ins-det↗

arXiv2025

Quantum Noise Reduction in the Space-based Gravitational Wave Antenna DECIGO Using Optical Springs and Homodyne Detection scheme

The DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a planned space-based, next-generation gravitational wave detector aimed at observing primordial gravitational waves originating form cosmic inflation. This work focuses on reducing the quantum noise, in the instrument's observation band of 0.1 to 10 Hz, by employing optical springs and a homodyne detection scheme. Although detuning 1000\,km long arm cavities was previously considered ineffective due to quantum state degradation from diffraction losses, we revisit this problem by formulating a new, rigorous model for quantum state of light by accounting for the vacuum state mixing as a result of diffraction losses. This work shows that high sensitivities can be achieved by employing optimal configurations of optical springs and homodyne detection schemes even with diffraction losses. These improvements alone are still not sufficient to achieve sensitivities to detect primordial gravitational waves as other technical noises limit further improvement.

gr-qc↗

arXiv2025

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

We propose the Jiggled Interferometer (JIGI), a novel ground-based gravitational wave detector employing low-frequency noise mitigation similar to that of space-based detectors. Using rapidly-repeated free-fall test masses, JIGI eliminates seismic and suspension thermal noise during free fall. Compared to the Juggled Interferometer, it offers improved angular stability and avoids tracking lasers. We analyze detrending -- a required step to remove actuation-induced noise -- and show sensitivity gains of about four orders of magnitude in the 0.1-0.3 Hz band, relative to seismic and suspension noise extrapolated from the Cosmic Explorer.

gr-qc↗

arXiv2025

Proof-of-Principle Experiment on a Displacement-Noise-Free Neutron Interferometer for Gravitational Wave Detection

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 (J- PARC). 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.

physics.ins-det↗

arXiv2025

Adjusting optical cavity birefringence with wavelength tunable laser for axion searches

Axions have attracted attention as promising candidates for dark matter (DM). Although axions have been intensively searched for, they have not been observed yet. Recently, novel experiments to search for axion DM have been proposed that use optical cavities to amplify polarization rotation of laser light induced by the axion-photon interaction. One such experiment employs a ring cavity composed of four mirrors. However, its sensitivity to the axion-photon coupling $g_{a\gamma}$ in the low axion mass region is limited due to a reflection phase difference between s- and p-polarizations. In this paper, we propose a new method to improve the sensitivity using zero-phase shift mirrors and a wavelength tunable laser. Moreover, the laser makes it easier to scan the high axion mass region by tuning the reflection phase difference between s- and p-polarizations. We experimentally confirmed that the phase difference generated upon reflection on a zero phase shift mirror satisfied the requirement of $8.6 \times 10^{-3}~\mathrm{deg}$, which corresponds to the half width at half maximum (HWHM) of the cavity for p-polarization with the mirror fixed on a folded cavity and a wavelength tunable laser.

hep-ex↗

arXiv2025

Observation of an Optical Spring in a Robustly Controlled Signal-Recycled Michelson Interferometer

We present, to the best of our knowledge, the first demonstration of an optical spring in a signal-recycled Michelson interferometer without arm cavities. The setup utilizes multiple laser fields to achieve stable and precisely controllable detuning and incorporates a compliant suspension system comprising two double-spiral springs. These results support optical spring-enhanced interferometers with intracavity amplification, offering a promising avenue for improving high-frequency sensitivity in future gravitational-wave detectors.

physics.optics↗

arXiv2025

Quantum Noise from Vacuum Field Injection in Optical Cavities with Diffraction-related Loss

The space-based gravitational wave detector DECIGO is designed to observe primordial gravitational waves with 1,000 km Fabry-Perot cavities. Its sensitivity is limited by quantum noise, and although squeezing can suppress it, its effectiveness is reduced by diffraction-related loss, which leads to the injection of vacuum fields into the interferometer. This paper presents a rigorous treatment of quantum field propagation in the presence of diffraction and higher-order mode losses, deriving input-output relations, and modeling their impact via an optomechanical block diagram. The analysis shows that diffraction-induced vacuum fields slightly increase radiation pressure noise, while shot noise remains unaffected. Nevertheless, cavity detuning with homodyne detection yields a dip in the noise spectrum. By accurately capturing these effects, this framework enables a detailed study of sensitivity improvements made by either just detuning the main cavity while implementing homodyne detection, or by combining this with optical-spring quantum locking using auxiliary cavities, laying a firm foundation for enhancing DECIGO's capability to detect primordial gravitational waves.

physics.optics↗

arXiv2025

SILVIA: Ultra-precision formation flying demonstration for space-based interferometry

We propose SILVIA (Space Interferometer Laboratory Voyaging towards Innovative Applications), a mission concept designed to demonstrate ultra-precision formation flying between three spacecraft separated by 100 m. SILVIA aims to achieve sub-micrometer precision in relative distance control by integrating spacecraft sensors, laser interferometry, low-thrust and low-noise micro-propulsion for real-time measurement and control of distances and relative orientations between spacecraft. A 100-meter-scale mission in a near-circular low Earth orbit has been identified as an ideal, cost-effective setting for demonstrating SILVIA, as this configuration maintains a good balance between small relative perturbations and low risk for collision. This mission will fill the current technology gap towards future missions, including gravitational wave observatories such as DECIGO (DECihertz Interferometer Gravitational wave Observatory), designed to detect the primordial gravitational wave background, and high-contrast nulling infrared interferometers like LIFE (Large Interferometer for Exoplanets), designed for direct imaging of thermal emissions from nearby terrestrial planet candidates. The mission concept and its key technologies are outlined, paving the way for the next generation of high-precision space-based observatories.

astro-ph.IM↗

arXiv2025

Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO

DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1-10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1,000 km sides, forming Fabry-P\'erot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry-P\'erot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry-P\'erot cavities of DECIGO and B-DECIGO.

gr-qc↗

arXiv2025

Enhancing the sensitivity to ultralight bosonic dark matter using signal correlations

In recent years, numerous experiments have been proposed and conducted to search for ultralight bosonic dark matter (ULBDM). Signals from ULBDM in such experiments are characterized by extremely narrow spectral widths. A near-optimal detection strategy is to divide the data based on the signal coherence time and sum the power across these segments. However, the signal coherence time can extend beyond a day, making it challenging to construct contiguous segments of such a duration due to detector instabilities. In this work, we present a novel detection statistic that can coherently extract ULBDM signals from segments of arbitrary durations. Our detection statistic, which we refer to as coherent SNR, is a weighed sum of data correlations, whose weights are determined by the expected signal correlations. We demonstrate that coherent SNR achieves sensitivity independent of segment duration and surpasses the performance of the conventional incoherent-sum approach, through analytical arguments and numerical experiments.

hep-ph↗

arXiv2025

Searches for ultralight vector and axion dark matter with KAGRA

We have proposed using laser interferometric gravitational wave detectors to search for ultralight vector and axion dark matter. Vector dark matter can be probed through oscillating forces on suspended mirrors, while axion dark matter can be detected via oscillating polarization rotation of laser beams. This paper reviews these searches with the KAGRA detector in Japan, including the first vector dark matter search with KAGRA's 2020 data and installation of polarization optics for axion dark matter search during the upcoming 2025 observing run.

hep-ph↗

arXiv2024

TOrsion-Bar Antenna: A Ground-Based Detector for Low-Frequency Gravity Gradient Measurement

The Torsion-Bar Antenna (TOBA) is a torsion pendulum-based gravitational detector developed to observe gravitational waves in frequencies between 1 mHz and 10 Hz. The low resonant frequency of the torsion pendulum enables observation in this frequency band on the ground. The final target of TOBA is to observe gravitational waves with a 10 m detector and expand the observation band of gravitational waves. In this paper, an overview of TOBA, including the previous prototype experiments and the current ongoing development, is presented.

gr-qc↗

arXiv2024

Characterisation of birefringence inhomogeneity of KAGRA sapphire mirrors from transmitted wavefront error measurements

Cooling down test masses to cryogenic temperatures is a way to reduce the thermal noise of gravitational wave detectors. Crystalline materials are considered the most promising materials for fabricating cryogenic test masses and their coatings because of their excellent thermal and optical properties at low temperatures. However, birefringence owing to local impurities and inhomogeneities in the crystal can degrade the performance of the detector. The birefringence measurement or mapping over a two-dimensional area is thus important. This study describes a method for fast birefringence measurements of a large sample by simply combining a series of transmission wavefront error measurements using linearly polarised light with Fizeau interferometers. Using this method, the birefringence inhomogeneity information of KAGRA's two input test masses with a diameter of 22 cm was fully reconstructed. The birefringence information was then used to calculate the transverse beam shapes of the light fields in orthogonal polarisation directions when passing through the substrate. It was possible to find a calculated beam shape consistent with in-situ measurements using the KAGRA interferometer. This technique is crucial for birefringence characterisation of test masses in future detectors, where even larger sizes are used.

physics.optics↗

arXiv2023

Sagnac-type neutron displacement-noise-free interferometeric gravitational-wave detector

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.

gr-qc↗

arXiv2023

Kerr-Enhanced Optical Spring

We propose and experimentally demonstrate the generation of enhanced optical springs using the optical Kerr effect. A nonlinear optical crystal is inserted into a Fabry-Perot cavity with a movable mirror, and a chain of second-order nonlinear optical effects in the phase-mismatched condition induces the Kerr effect. The optical spring constant is enhanced by a factor of $1.6\pm0.1$ over linear theory. To our knowledge, this is the first realization of optomechanical coupling enhancement using a nonlinear optical effect, which has been theoretically investigated to overcome the performance limitations of linear optomechanical systems. The tunable nonlinearity of demonstrated system has a wide range of potential applications, from observing gravitational waves emitted by binary neutron star post-merger remnants to cooling macroscopic oscillators to their quantum ground state.

quant-ph↗

arXiv2023

Optimization of quantum noise in space gravitational-wave antenna DECIGO with optical-spring quantum locking considering mixture of vacuum fluctuations in homodyne detection

Quantum locking using optical spring and homodyne detection has been devised to reduce quantum noise that limits the sensitivity of DECIGO, a space-based gravitational wave antenna in the frequency band around 0.1 Hz for detection of primordial gravitational waves. The reduction in the upper limit of energy density ${\Omega}_{\mathrm{GW}}$ from $2{\times}10^{-15}$ to $1{\times}10^{-16}$, as inferred from recent observations, necessitates improved sensitivity in 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.

gr-qc↗