arXiv subjects

Kentaro Somiya

Publications and source records attributed to Kentaro Somiya.

At least 19 recordsLinked to original sources

arXiv2026

Cyclic-Quadrature Intracavity Signal Amplification for Gravitational-Wave Detectors

The high-frequency sensitivity of laser-interferometric gravitational-wave detectors is limited by quantum shot noise. Increasing the circulating optical power reduces shot noise, but is constrained by thermal effects and optomechanical instabilities. We propose cyclic-quadrature intracavity signal amplification, in which an optical parametric amplifier (OPA) inside a detuned signal-recycling cavity is used as a phase-sensitive amplifier of the gravitational-wave signal quadrature. By detuning the signal-recycling cavity for $\pi$/4, the optical quadratures rotate by $\pi$/2 on each round trip, so a signal generated in the phase quadrature appears in the readout phase quadrature only after odd-numbered passes through the OPA. Successive contributions to the readout phase quadrature, which are separated by two round trips, have alternating signs, making this two-round-trip evolution anti-resonant. During each two-round-trip cycle, however, the same field experiences one amplification and one deamplification, so neither vacuum squeezing nor parametric gain accumulates. Despite the destructive interference between signal contributions separated by two round trips, the OPA increases the signal component extracted through the output coupler, thereby improving the signal-to-noise ratio. When the OPA gain is sufficiently large, the response approaches that of an interferometer with an effective power enhancement of $1/\tau^2$, where $\tau$ is the amplitude transmissivity of the quadrature-rotation mirror that forms the amplifier cavity. We apply the proposed scheme to a current gravitational-wave detector with a near-future upgrade and show that it improves the quantum-noise-limited sensitivity over a broad frequency range extending into the kilohertz band.

physics.optics↗

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

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

Testing the quantum nature of gravity through interferometry

We propose a Michelson-type interferometric protocol for testing the quantum nature of gravity through testing the phenomenology of semi-classical gravity theory, which predicts a state-dependent Schrodinger-Newton (SN) evolution of the test mass. The protocol's feature lies in utilizing the asymmetry of two interferometric arms induced by SN self-gravity to create cross-talk between the common and differential motion of the test masses. This cross-talk is imprinted as a clean binary signature in the correlation measurements of the interferometer's output light fields. Our results demonstrate that, when assisted by 10 dB squeezed input states, 3 hours of aggregated measurement data can provide sufficient signal-to-noise ratio to conclusively test the SN theory in 1 Kelvin environment. This shows the strong feasibility of using such interferometric protocols to test if gravity operates quantum-mechanically.

quant-ph↗

arXiv2025

Quantum Back Action Evasion with Reservoir Engineering

We propose a back-action evading scheme for a free mass that combines reservoir engineering with velocity measurement. The underlying principle follows the double-pass-type speed meter, which measures the mirror's velocity using a nonreciprocal interaction. In our method, the nonreciprocal coupling is realized through reservoir engineering, following the recipe proposed in [Phys. Rev. X 5, 021025]. We show that reservoir engineering can reproduce the double-pass speed meter with optimal feedforward, using only reciprocal interactions. The resulting force sensitivity surpasses the standard quantum limit, providing an alternative route to quantum back-action evasion in cavity optomechanical systems.

quant-ph↗

arXiv2025

Teleportation-based Speed Meter for Precision Measurement

We propose a quantum teleportation-based speed meter for interferometric displacement sensing. Two equivalent implementations are presented: an online approach that uses real-time displacement operation and an offline approach that relies on post-processing. Both implementations reduce quantum radiation pressure noise and surpass the standard quantum limit of measuring displacement. We discuss potential applications to gravitational-wave detectors, where our scheme enhances low-frequency sensitivity without requiring modifications to the core optics of a conventional Michelson interferometer (e.g., substrate or coating properties). This approach offers a new path to back-action evasion enabled by quantum entanglement.

quant-ph↗

arXiv2024

Parameter estimation of protoneutron stars from gravitational wave signals using the Hilbert-Huang transform

Core-collapse supernovae (CCSNe) are potential multimessenger events detectable by current and future gravitational wave (GW) detectors. The GW signals emitted during these events are expected to provide insights into the explosion mechanism and the internal structures of neutron stars. In recent years, several studies have empirically derived the relationship between the frequencies of the GW signals originating from the oscillations of protoneutron stars (PNSs) and the physical parameters of these stars. This study applies the Hilbert-Huang transform (HHT) [Proc. R. Soc. A 454, 903 (1998)] to extract the frequencies of these modes to infer the physical properties of the PNSs. The results exhibit comparable accuracy to a short-time Fourier transform-based estimation, highlighting the potential of this approach as a complementary method for extracting physical information from GW signals of CCSNe.

gr-qc↗

arXiv2024

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↗

arXiv2024

Comparative study of 1D and 2D convolutional neural network models with attribution analysis for gravitational wave detection from compact binary coalescences

Recent advancements in gravitational wave astronomy have seen the application of convolutional neural networks (CNNs) in signal detection from compact binary coalescences. This study presents a comparative analysis of two CNN architectures: one-dimensional (1D) and two-dimensional (2D) along with an ensemble model combining both. We trained these models to detect gravitational wave signals from binary black hole (BBH) mergers, neutron star-black hole (NSBH) mergers, and binary neutron star (BNS) mergers within real detector noise. Our investigation entailed a comprehensive evaluation of the detection performance of each model type across different signal classes. To understand the models' decision-making processes, we employed feature map visualization and attribution analysis. The findings revealed that while the 1D model showed superior performance in detecting BBH signals, the 2D model excelled in identifying NSBH and BNS signals. Notably, the ensemble model outperformed both individual models across all signal types, demonstrating enhanced detection capabilities. Additionally, input feature visualization indicated distinct areas of focus in the data for the 1D and 2D models, emphasizing the effectiveness of their combination.

gr-qc↗

arXiv2023

Visualizing convolutional neural network for classifying gravitational waves from core-collapse supernovae

In this study, we employ a convolutional neural network to classify gravitational waves originating from core-collapse supernovae. Training is conducted using spectrograms derived from three-dimensional numerical simulations of waveforms, which are injected onto real noise data from the third observing run of both Advanced LIGO and Advanced Virgo. To gain insights into the decision-making process of the model, we apply class activation mapping techniques to visualize the regions in the input image that are significant for the model's prediction. The class activation maps reveal that the model's predictions predominantly rely on specific features within the input spectrograms, namely, the $g$-mode and low-frequency modes. The visualization of convolutional neural network models provides interpretability to enhance their reliability and offers guidance for improving detection efficiency.

astro-ph.IM↗

arXiv2022

Photothermal effect in macroscopic optomechanical systems with an intracavity nonlinear optical crystal

Intracavity squeezing is a promising technique that may improve the sensitivity of gravitational wave detectors and cool optomechanical oscillators to the ground state. However, the photothermal effect may modify the occurrence of optomechanical coupling due to the presence of a nonlinear optical crystal in an optical cavity. We propose a novel method to predict the influence of the photothermal effect by measuring the susceptibility of the optomechanical oscillator and identifying the net optical spring constant and photothermal absorption rate. Using this method, we succeeded in precisely estimating parameters related to even minor photothermal effects, which could not be measured using a previously developed method.

quant-ph↗

arXiv2022

Localization of gravitational waves using machine learning

An observation of gravitational waves is a trigger of the multi-messenger search of an astronomical event. A combination of the data from two or three gravitational wave telescopes indicates the location of a source and low-latency data analysis is key to transferring the information to other telescopes sensitive at different wavelengths. In contrast to the current method, which relies on the matched-filtering technique, we proposed the use of machine learning that is much faster and possibly more accurate than matched filtering. Our machine-learning method is a combination of the method proposed by Chatterjee {\it et al.} and a method using the temporal convolutional network. We demonstrate the sky localization of a gravitational-wave source using four telescopes: LIGO H1, LIGO L1, Virgo, and KAGRA, and compare the result in the case without KAGRA to examine the positive influence of having the fourth telescope in the global gravitational-wave network.

gr-qc↗

arXiv2021

Cryogenic suspension design for a kilometer-scale gravitational-wave detector

We report the mirror suspension design for Large-scale Cryogenic Gravitational wave Telescope, KAGRA, during bKAGRA Phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA Phase 1 are discussed.

physics.ins-det↗

arXiv2020

Prospects for improving the sensitivity of the cryogenic gravitational wave detector KAGRA

Upgrades to improve the sensitivity of gravitational wave detectors enable more frequent detections and more precise source parameter estimation. Unlike other advanced interferometric detectors such as Advanced LIGO and Advanced Virgo, KAGRA requires different approach for the upgrade since it is the only detector which employs cryogenic cooling of the test masses. In this paper, we describe possible KAGRA upgrades with technologies focusing on different detector bands, and compare the impacts on the detection of compact binary coalescences. We show that either fivefold improvement in the $100 M_{\odot}$--$100 M_{\odot}$ binary black hole range, a factor of 1.3 improvement in the binary neutron star range, or a factor of 1.7 improvement in the sky localization of binary neutron stars is well feasible with upgrades that do not require changes in the existing cryogenic or vacuum infrastructure. We also show that twofold broadband sensitivity improvement is possible by applying multiple upgrades to the detector.

gr-qc↗

arXiv2020

Current status of space gravitational wave antenna DECIGO and B-DECIGO

Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could be produced during the inflationary period right after the birth of the universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in the heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Perot Michelson interferometers with an arm length of 1,000 km. Three clusters of DECIGO will be placed far from each other, and the fourth cluster will be placed in the same position as one of the three clusters to obtain the correlation signals for the detection of the primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder of DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand the multi-messenger astronomy.

gr-qc↗

arXiv2020

Estimation of losses in a 300 m filter cavity and quantum noise reduction in the KAGRA gravitational-wave detector

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-Pérot 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.

astro-ph.IM↗

arXiv2019

Quantum noise reduction techniques in KAGRA

KAGRA is the first large-scale gravitational-wave detector with cryogenic test masses. Its target sensitivity is limited mostly by quantum noise in the observation frequency band owing to the remarkable reduction of thermal noise at cryogenic temperatures. It is thus essential to reduce quantum noise, and KAGRA is designed to implement two quantum noise reduction techniques. KAGRA has already started considering an upgrade plan, in which a few more new quantum noise reduction techniques will be incorporated. In this article, we report the currently implemented quantum noise reduction techniques for KAGRA and those that will be implemented in the near future.

physics.optics↗

arXiv2019

Design and experimental demonstration of a laser modulation system for future gravitational-wave detectors

Detuning the signal-recycling cavity length from a cavity resonance significantly improves the quantum noise beyond the standard quantum limit, while there is no km-scale gravitational-wave detector successfully implemented the technique. The detuning technique is known to introduce great excess noise, and such noise can be reduced by a laser modulation system with two Mach-Zehnder interferometers in series. This modulation system, termed Mach-Zehnder Modulator (MZM), also makes the control of the gravitational-wave detector more robust by introducing the third modulation field which is non-resonant in any part of the main interferometer. On the other hand, mirror displacements of the Mach-Zehnder interferometers arise a new kind of noise source coupled to the gravitational-wave signal port. In this paper, the displacement noise requirement of the MZM is derived, and also results of our proof-of-principle experiment is reported.

astro-ph.IM↗