arXiv subjects

Kyohei Yamada

Publications and source records attributed to Kyohei Yamada.

18 recordsLinked to original sources

arXiv2026

The Simons Observatory: Overview of the Cryogenic Half-wave Plate Polarization Modulators

The Simons Observatory (SO) is a ground-based Cosmic Microwave Background (CMB) experiment that is located in the Atacama plateau. The Small Aperture Telescopes (SATs) of SO are optimized for polarimetry on the degree scale. Atmospheric $1/f$ contamination of the CMB signal poses a significant challenge for observations at this angular scale. In order to control the $1/f$ noise, the SATs utilize a Cryogenic Half-Wave Plate (CHWP) in their optics. The CHWP modulates the polarization signal to a higher frequency to separate it from the unpolarized atmospheric noise. Precision measurements of the CHWP rotation angle are required to successfully recover the target polarized signals. We present a method to reconstruct the CHWP rotation angle that achieves a noise level of 0.16 $\mu\mathrm{rad\sqrt{s}}$, meeting our requirement.

astro-ph.IM↗

arXiv2026

The Simons Observatory: Rotation Performance of Cryogenic Half-Wave Plate Polarization Modulators

We present the on-site rotation performance of the first three cryogenic continuously rotating half-wave plate (HWP) polarization modulators for the Simons Observatory small aperture telescopes (SATs). The SATs operate at an altitude of 5200 m in the Atacama Desert in northern Chile, and measure the degree-scale cosmic microwave background polarization to search for primordial $B$-mode polarization. To this end, the SATs employ a 505 mm diameter 50 K cryogenic HWP polarization modulator to suppress atmospheric $1/f$ noise and to mitigate systematic uncertainties. We present methods for reconstructing the rotation of our polarization modulators, enabling detailed evaluations of their rotation angle accuracy, stability, displacements, and vibrations. We achieve the required rotation angle accuracy in more than 99.9% of observations, with a median noise level of 0.16 $\mu$rad$\sqrt{\text{s}}$. We also achieve one-dimensional measurement of the rotor displacement with an accuracy of 0.06 $\mu\text{m}\sqrt{\text{s}}$. Our results demonstrate the on-site rotation performance, rotation angle reconstruction method, and robustness of the polarization angle modulators. This is a crucial step towards achieving the SAT science goals.

astro-ph.IM↗

arXiv2026

The Simons Observatory: On-sky performance of radio-transparent multi-layer insulation (RT-MLI) using Styroace-II Styrofoam

We present the on-sky performance of a Radio-Transparent Multi-Layer Insulation filter (RT-MLI) that uses Styroace-II styrofoam to reject ambient thermal radiation from entering a 0.42 m diameter aperture to a sub-100 mK bolometric detector array cooled by a dilution-refrigerator. We find that greater than 90% of the expected incident infra-red (IR) radiation is rejected, resulting in $<$12 W of measured transmitted power. Transmitted power in the detector passbands is consistent with a lower bound of 95%. We address filter design and placement, thermal loading, and mm-wave transmission.

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arXiv2025

The Simons Observatory: Detector Polarization Angle Calibration using Sparse Wire Grid with Initial Data Sets of the Small Aperture Telescope

Improved measurements of $B$-modes in the cosmic microwave background can be obtained through accurate calibration of the orientation of detector antennas as projected onto the sky. Miscalibration of the detector polarization angle leads to a leakage of $E$-modes into $B$-modes, which can bias the detection of the latter. To achieve a $\sigma(r)$ of 0.003, the Simons Observatory Small Aperture Telescopes are required to calibrate the global polarization angle on the sky with an accuracy ${\lesssim}0.1^\circ$. We demonstrate a fully remote-controllable calibration system using a ``sparse wire grid," which injects a rotatable linear polarized signal across the telescope's focal plane. This calibration system is installed and operational on a Small Aperture Telescope at its observing site at the Parque Astron\'omico in the Atacama desert in Chile. We developed a pipeline for the detector polarization angle calibration, and demonstrate it using initial data for 93~GHz and 145~GHz frequency bands. The observed distribution of detector polarization angles is in agreement with the instrument design. Statistical uncertainties for the relatively calibrated polarization angles are $0.02^\circ$ and $0.03^\circ$ at 93~GHz and 145~GHz, respectively. Systematic uncertainty was evaluated to be $0.08^\circ$ at the hardware development and fabrication stage. Their sum in quadrature is less than $0.1^\circ$.

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arXiv2025

Constraints on the polarization angle oscillations of the Crab Nebula with the Simons Array and its applications to the search for axion-like particles

We present a search for polarization oscillation of the Crab Nebula, also known as Tau A, at millimeter wavelengths using observations with the Simons Array, the successor experiment to POLARBEAR. We follow up on previous work by POLARBEAR using 90 GHz band data of the 2023 observing season of the Simons Array to evaluate the variability of Tau A's polarization angle. Tau A is widely used as a polarization angle calibration source in millimeter-wave astronomy, and thus it is necessary to validate the stability. Additionally, an interesting application of the time-resolved polarimetry of Tau A is to search for axion-like particles (ALPs). We do not detect a global signal across the frequencies considered in this analysis and place a median 95% upper bound of polarization oscillation amplitude $A<0.12^{\circ}$ over oscillation frequencies from 3.39 year$^{-1}$ to 1.50 day$^{-1}$. This constrains the ALP-photon coupling at a median 95% upper bound of $g_{a\gamma\gamma}< 3.84\times 10^{-12}\times\left(m_a/10^{-21}\,\mathrm{eV}\right)$ in the mass range from $4.4\times10^{-22}$ to $7.2\times10^{-20}$ eV, assuming the ALP constitutes all of dark matter, its field is a stochastic Gaussian field, and it is the sole source of Tau A's polarization angle oscillation. Additionally, we do not detect signal at the frequencies where 2.5$\sigma$ hints were previously reported by POLARBEAR, but we do not exclude these signals at the 95% confidence level.

astro-ph.CO↗

arXiv2025

The Simons Observatory: Large Diameter and Large Load-Capacity Superconducting Magnetic Bearing for a Millimeter-Wave Polarization Modulator

We present the design methodology and characterization of a superconducting magnetic bearing (SMB) system for the polarization modulator in the SAT-LF, one of the small aperture telescopes (SATs) in the Simons Observatory (SO) that is sensitive at 30/40 GHz frequency bands. SO is a ground-based cosmic microwave background (CMB) polarization experiment, with the SATs specifically aiming to search for primordial parity-odd polarization anisotropies at degree scales. Each SAT is equipped with a cryogenic, continuously rotating half-wave plate (HWP) as a polarization modulator to mitigate atmospheric $1/f$ noise and instrumental systematics. The HWP system employs an SMB, consisting of a ring-shaped magnet and superconductor, to achieve a 550 mm clear aperture and stable 2 Hz rotation at a temperature of around 50 K. One challenge for the HWP system in the SAT-LF is the large 35 kg load on the SMB due to the thicker HWP than in previous telescopes. Since the SMB stiffness is critical for maintaining the alignment of the HWP in the telescope, we developed a method to quantitatively predict the stiffness using finite element simulations with the so-called H-formulation. We evaluated the stiffness for various geometries of the magnet and superconductor, thereby optimizing their dimensions. The prediction is in excellent agreement with experimental measurements of the fabricated SMB, demonstrating a $\sim$5\% accuracy. We also demonstrated that the SMB achieves sufficiently low friction-induced heat dissipation, measured at 0.26 W when rotating at 2 Hz. The design methodology and the implementation of the SMB demonstrated here not only provides an enabling technology for the SO SAT-LF, but also is a crucial stepping stone for future CMB experiments that make use of HWP polarization modulators.

astro-ph.IM↗

arXiv2025

The Simons Observatory: Validation of reconstructed power spectra from simulated filtered maps for the Small Aperture Telescope survey

We present a transfer function-based method to estimate angular power spectra from filtered maps for cosmic microwave background (CMB) surveys. This is especially relevant for experiments targeting the faint primordial gravitational wave signatures in CMB polarisation at large scales, such as the Simons Observatory (SO) small aperture telescopes. While timestreams can be filtered to mitigate the contamination from low-frequency noise, usual methods that calculate the mode coupling at individual multipoles can be challenging for experiments covering large sky areas or reaching few-arcminute resolution. The method we present here, although approximate, is more practical and faster for larger data volumes. We validate it through the use of simulated observations approximating the first year of SO data, going from half-wave plate-modulated timestreams to maps, and using simulations to estimate the mixing of polarisation modes induced by an example of time-domain filtering. We show its performance through an example null test and with an end-to-end pipeline that performs inference on cosmological parameters, including the tensor-to-scalar ratio $r$. The performance demonstration uses simulated observations at multiple frequency bands. We find that the method can recover unbiased parameters for our simulated noise levels.

astro-ph.CO↗

arXiv2024

A measurement of atmospheric circular polarization with POLARBEAR

At millimeter wavelengths, the atmospheric emission is circularly polarized owing to the Zeeman splitting of molecular oxygen by the Earth's magnetic field. We report a measurement of the signal in the 150 GHz band using 3 years of observational data with the \textsc{Polarbear} project. Non-idealities of a continuously rotating half-wave plate (HWP) partially convert circularly polarized light to linearly polarized light. While \textsc{Polarbear} detectors are sensitive to linear polarization, this effect makes them sensitive to circular polarization. Although this was not the intended use, we utilized this conversion to measure circular polarization. We reconstruct the azimuthal gradient of the circular polarization signal and measure its dependency from the scanning direction and the detector bandpass. We compare the signal with a simulation based on atmospheric emission theory, the detector bandpass, and the HWP leakage spectrum model. We find the ratio of the observed azimuthal slope to the simulated slope is $0.92 \pm 0.01\rm{(stat)} \pm 0.07\rm{(sys)}$. This ratio corresponds to a brightness temperature of $3.8\,\mathrm{m K}$ at the effective band center of $121.8\,\mathrm{GHz}$ and bandwidth of $3.5\,\mathrm{GHz}$ estimated from representative detector bandpass and the spectrum of Zeeman emission. This result validates our understanding of the instrument and reinforces the feasibility of measuring the circular polarization using the imperfection of continuously rotating HWP. Continuously rotating HWP is popular in ongoing and future cosmic microwave background experiments to modulate the polarized signal. This work shows a method for signal extraction and leakage subtraction that can help measuring circular polarization in such experiments.

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arXiv2024

Exploration of the polarization angle variability of the Crab Nebula with POLARBEAR and its application to the search for axion-like particles

The Crab Nebula, also known as Tau A, is a polarized astronomical source at millimeter wavelengths. It has been used as a stable light source for polarization angle calibration in millimeter-wave astronomy. However, it is known that its intensity and polarization vary as a function of time at a variety of wavelengths. Thus, it is of interest to verify the stability of the millimeter-wave polarization. If detected, polarization variability may be used to better understand the dynamics of Tau~A, and for understanding the validity of Tau~A as a calibrator. One intriguing application of such observation is to use it for the search of axion-like particles (ALPs). Ultralight ALPs couple to photons through a Chern-Simons term, and induce a temporal oscillation in the polarization angle of linearly polarized sources. After assessing a number of systematic errors and testing for internal consistency, we evaluate the variability of the polarization angle of the Crab Nebula using 2015 and 2016 observations with the 150 GHz POLARBEAR instrument. We place a median 95% upper bound of polarization oscillation amplitude $A < 0.065^\circ$ over the oscillation frequencies from $0.75~\mathrm{year}^{-1}$ to $0.66~\mathrm{hour}^{-1}$. Assuming that no sources other than ALP are causing Tau A's polarization angle variation, that the ALP constitutes all the dark matter, and that the ALP field is a stochastic Gaussian field, this bound translates into a median 95% upper bound of ALP-photon coupling $g_{aγγ} < 2.16\times10^{-12}\,\mathrm{GeV}^{-1}\times(m_a/10^{-21} \mathrm{eV})$ in the mass range from $9.9\times10^{-23} \mathrm{eV}$ to $7.7\times10^{-19} \mathrm{eV}$. This demonstrates that this type of analysis using bright polarized sources is as competitive as those using the polarization of cosmic microwave background in constraining ALPs.

astro-ph.CO↗

arXiv2024

The Simons Observatory: Deployment of the observatory control system and supporting infrastructure

The Simons Observatory (SO) is a cosmic microwave background (CMB) observatory consisting of three small aperture telescopes and one large aperture telescope. SO is located in the Atacama Desert in Chile at an elevation of 5180m. Distributed among the four telescopes are over 60,000 transition-edge sensor (TES) bolometers across six spectral bands centered between 27 and 280 GHz. A large collection of ancillary hardware devices which produce lower rate `housekeeping' data are used to support the detector data collection. We developed a distributed control system, which we call the observatory control system (ocs), to coordinate data collection among all systems within the observatory. ocs is a core component of the deployed site software, interfacing with all on-site hardware. Alongside ocs we utilize a combination of internally and externally developed open source projects to enable remote monitoring, data management, observation coordination, and data processing. Deployment of a majority of the software is done using Docker containers. The deployment of software packages is partially done via automated Ansible scripts, utilizing a GitOps based approach for updating infrastructure on site. We describe an overview of the software and computing systems deployed within SO, including how those systems are deployed and interact with each other. We also discuss the timing distribution system and its configuration as well as lessons learned during the deployment process and where we plan to make future improvements.

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arXiv2024

The Simons Observatory: Alarms and Detector Quality Monitoring

The Simons Observatory (SO) is a group of modern telescopes dedicated to observing the polarized cosmic microwave background (CMB), transients, and more. The Observatory consists of four telescopes and instruments, with over 60,000 superconducting detectors in total, located at ~5,200 m altitude in the Atacama Desert of Chile. During observations, it is important to ensure the detectors, telescope platforms, calibration and receiver hardware, and site hardware are within operational bounds. To facilitate rapid response when problems arise with any part of the system, it is essential that alerts are generated and distributed to appropriate personnel if components exceed these bounds. Similarly, alerts are generated if the quality of the data has become degraded. In this paper, we describe the SO alarm system we developed within the larger Observatory Control System (OCS) framework, including the data sources, alert architecture, and implementation. We also present results from deploying the alarm system during the commissioning of the SO telescopes and receivers.

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arXiv2024

The Simons Observatory: Design, integration, and testing of the small aperture telescopes

The Simons Observatory (SO) is a cosmic microwave background (CMB) survey experiment that includes small-aperture telescopes (SATs) observing from an altitude of 5,200 m in the Atacama Desert in Chile. The SO SATs will cover six spectral bands between 27 and 280 GHz to search for primordial B-modes to a sensitivity of $σ(r)=0.002$, with quantified systematic errors well below this value. Each SAT is a self-contained cryogenic telescope with a 35$^\circ$ field of view, 42 cm diameter optical aperture, 40 K half-wave plate, 1 K refractive optics, and $<0.1$ K focal plane that holds $>12,000$ TES detectors. We describe the nominal design of the SATs and present details about the integration and testing for one operating at 93 and 145 GHz.

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arXiv2024

The Simons Observatory: Development and Optical Evaluation of Achromatic Half-Wave Plates

The Simons Observatory (SO) experiment is a cosmic microwave background (CMB) experiment located in the Atacama Desert, Chile. The SO' s small aperture telescopes (SATs) consist of three telescopes designed for precise CMB polarimetry at large angular scales. Each SAT uses a cryogenic rotating half-wave plate (HWP) as a polarization modulator to mitigate atmospheric 1/f noise and other systematics. To realize efficient polarization modulation over the observation bands, we fabricated an achromatic HWP (AHWP) consisting of three sapphire plates with anti-reflection coatings. The AHWP is designed to have broadband modulation efficiency and transmittance. This paper reports on the design and the preliminary characterization of the AHWPs for SATs.

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arXiv2023

The Simons Observatory: A fully remote controlled calibration system with a sparse wire grid for cosmic microwave background telescopes

For cosmic microwave background (CMB) polarization observations, calibration of detector polarization angles is essential. We have developed a fully remote controlled calibration system with a sparse wire grid that reflects linearly polarized light along the wire direction. The new feature is a remote-controlled system for regular calibration, which has not been possible in sparse wire grid calibrators in past experiments. The remote control can be achieved by two electric linear actuators that load or unload the sparse wire grid into a position centered on the optical axis of a telescope between the calibration time and CMB observation. Furthermore, the sparse wire grid can be rotated by a motor. A rotary encoder and a gravity sensor are installed on the sparse wire grid to monitor the wire direction. They allow us to achieve detector angle calibration with expected systematic error of $0.08^{\circ}$. The calibration system will be installed in small-aperture telescopes at Simons Observatory.

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arXiv2023

Constraints on axion-like polarization oscillations in the cosmic microwave background with POLARBEAR

Very light pseudoscalar fields, often referred to as axions, are compelling dark matter candidates and can potentially be detected through their coupling to the electromagnetic field. Recently a novel detection technique using the cosmic microwave background (CMB) was proposed, which relies on the fact that the axion field oscillates at a frequency equal to its mass in appropriate units, leading to a time-dependent birefringence. For appropriate oscillation periods this allows the axion field at the telescope to be detected via the induced sinusoidal oscillation of the CMB linear polarization. We search for this effect in two years of POLARBEAR data. We do not detect a signal, and place a median $95 \%$ upper limit of $0.65 ^\circ$ on the sinusoid amplitude for oscillation frequencies between $0.02\,\text{days}^{-1}$ and $0.45\,\text{days}^{-1}$, which corresponds to axion masses between $9.6 \times 10^{-22} \, \text{eV}$ and $2.2\times 10^{-20} \,\text{eV}$. Under the assumptions that 1) the axion constitutes all the dark matter and 2) the axion field amplitude is a Rayleigh-distributed stochastic variable, this translates to a limit on the axion-photon coupling $g_{ϕγ} < 2.4 \times 10^{-11} \,\text{GeV}^{-1} \times ({m_ϕ}/{10^{-21} \, \text{eV}})$.

astro-ph.CO↗

arXiv2023

Case-based Similar Image Retrieval for Weakly Annotated Large Histopathological Images of Malignant Lymphoma Using Deep Metric Learning

In the present study, we propose a novel case-based similar image retrieval (SIR) method for hematoxylin and eosin (H&E)-stained histopathological images of malignant lymphoma. When a whole slide image (WSI) is used as an input query, it is desirable to be able to retrieve similar cases by focusing on image patches in pathologically important regions such as tumor cells. To address this problem, we employ attention-based multiple instance learning, which enables us to focus on tumor-specific regions when the similarity between cases is computed. Moreover, we employ contrastive distance metric learning to incorporate immunohistochemical (IHC) staining patterns as useful supervised information for defining appropriate similarity between heterogeneous malignant lymphoma cases. In the experiment with 249 malignant lymphoma patients, we confirmed that the proposed method exhibited higher evaluation measures than the baseline case-based SIR methods. Furthermore, the subjective evaluation by pathologists revealed that our similarity measure using IHC staining patterns is appropriate for representing the similarity of H&E-stained tissue images for malignant lymphoma.

cs.CV↗

arXiv2021

Simons Observatory Small Aperture Telescope overview

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment from the Atacama Desert in Chile comprising three small-aperture telescopes (SATs) and one large-aperture telescope (LAT). In total, SO will field over 60,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities. In this work, we focus on the SATs which are optimized to search for primordial gravitational waves that are detected as parity-odd polarization patterns called a B-modes on degree scales in the CMB. Each SAT employs a single optics tube with TES arrays operating at 100 mK. The high throughput optics system has a 42 cm aperture and a 35-degree field of view coupled to a 36 cm diameter focal plane. The optics consist of three metamaterial anti-re ection coated silicon lenses. Cryogenic ring baffles with engineered blackbody absorbers are installed in the optics tube to minimize the stray light. The entire optics tube is cooled to 1 K. A cryogenic continuously rotating half-wave plate near the sky side of the aperture stop helps to minimize the effect of atmospheric uctuations. The telescope warm baffling consists of a forebaffle, an elevation stage mounted co-moving shield, and a fixed ground shield that together control the far side-lobes and mitigates ground-synchronous systematics. We present the status of the SAT development.

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arXiv2018

First demonstration of gamma-ray imaging using balloon-borne emulsion telescope

We promote the precise gamma-ray observation project Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE), which uses balloon-borne emulsion gamma-ray telescopes. The emulsion telescope realizes observations with high angular resolution, polarization sensitivity, and large aperture area in the 0.01--100 GeV energy region. Herein, we report the data analysis of emulsion tracks and the first demonstration of gamma-ray imaging via an emulsion telescope by using the flight data from the balloon experiment performed in 2015 (GRAINE 2015). The emulsion films were scanned by the latest read-out system for a total area of 41 m$^2$ in three months, and then the gamma-ray event selection was automatically processed. Millions of electron-pair events are accumulated in the balloon-borne emulsion telescope. The emulsion telescope detected signals from a calibration source (gamma rays from the interaction of cosmic rays with an aluminum plate) with a high significance during the balloon observation and created a gamma-ray image consistent with the source size and the expected angular resolution in the energy range of 100--300 MeV. The flight performance obtained in the GRAINE 2015 experiment proves that balloon-borne emulsion telescope experiments with larger area are feasible while maintaining expected imaging performance.

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