arXiv subjects

Takumi Kato

Publications and source records attributed to Takumi Kato.

14 recordsLinked to original sources

arXiv2026

First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023

Please check the paper for full abstract. The Galactic Center Excess (GCE) is an unexplained excess of gamma-ray emission from the Galactic Center. The GRAINE experiment aims to reveal the origin of the GCE using an emulsion gamma-ray telescope with high angular resolutions of 1 deg at 100 MeV and 0.1 deg at 1 GeV. In this study, we search for the GCE in a small region near the Galactic Center using the GRAINE 2023 flight data. In particular, rather than focusing on the spectral peak of the GCE at 2 GeV, we focused on the energy range below 300 MeV, where the spectral differences between the dark matter annihilation and millisecond pulsar scenarios are more pronounced. We searched for the GCE within 1 deg of the Galactic Center in the 75--300 MeV energy range. Although no significant excess was observed, we obtained an upper limit on the GCE flux of 1.70*10^-7 GeV cm^-2 s^-1 at the 2 sigma confidence level for the 1deg-radius ROI centered on the Galactic Center, based on a direct observation of the narrow region around the Galactic Center. This observation requires high angular resolution and represents a unique result from GRAINE. The obtained upper limit is consistent with the GCE flux near the Galactic Center, which was estimated from existing Fermi-LAT observations using a wide ROI and assuming an NFW profile. Although the current upper limit constrains some models, the available statistics are still insufficient to distinguish between the dark matter annihilation and millisecond pulsar scenarios, and both remain consistent with the current results. We also estimated the projected sensitivity of future GRAINE experiments based on the present observation and demonstrated their potential to probe the origin of the GCE by comparing the projected sensitivity with the predicted GCE spectra.

astro-ph.HE↗

arXiv2026

First overnight balloon flight of the GRAINE 2023 emulsion gamma-ray telescope enabled by a large-scale pressure-vessel gondola

The Gamma-Ray Astro Imager with Nuclear Emulsion (GRAINE) project conducts precision observations of sub-GeV--GeV cosmic gamma rays using a balloon-borne nuclear-emulsion telescope with high angular resolution. In GRAINE 2023, a 2.5-m$^{2}$ telescope was flown in the project's first overnight balloon flight, including observation periods for the Vela pulsar and Galactic center region. To operate the telescope under the low-pressure and low-temperature stratospheric environment, the balloon-style pressure-vessel concept was scaled up to a lightweight gondola with an internal length of 4.9 m. A new aluminum-alloy ring structure and a lightweight membranous-shell material, SHL-300MDL, were developed. While the telescope aperture was increased by a factor of 6.6 over GRAINE 2018, the pressure-vessel gondola mass was limited to 179 kg. Ground tests of the completed flight assembly demonstrated a differential pressure above 100 hPa at room temperature and at a mean temperature of $-66.0^{\circ}$C. The payload was launched from Alice Springs, Australia, in April 2023 and achieved a total flight duration of approximately 27 h, including 24.3 h of level flight. Although the upper membranous shell reached approximately $-60^{\circ}$C at night, the vessel internal pressure remained above the required 100 hPa throughout level flight. These results demonstrate that the developed gondola can accommodate a 2.5-m$^{2}$ emulsion gamma-ray telescope and maintain the required pressure during overnight stratospheric flight. Scientific analyses of astrophysical and atmospheric gamma rays, including dedicated analysis of the Galactic center region, are ongoing using the recovered emulsion data. This development provides a technical basis for repeated observations with future large-area GRAINE telescopes.

astro-ph.IM↗

arXiv2026

On-Demand Instructional Material Providing Agent Based on MLLM for Tutoring Support

Effective instruction in tutoring requires promptly providing instructional materials that match the needs of each student (e.g., in response to questions). In this study, we introduce an agent that automatically delivers supplementary materials on demand during one-on-one tutoring sessions. Our agent uses a multimodal large language model to analyze spoken dialogue between the instructor and the student, automatically generate search queries, and retrieve relevant Web images. Evaluation experiments demonstrate that our agent reduces the average image retrieval time by 44.4 s compared to cases without support and successfully provides images of acceptable quality in 85.7% of trials. These results indicate that our agent effectively supports instructors during tutoring sessions.

cs.HC↗

arXiv2025

QCoder Benchmark: Bridging Language Generation and Quantum Hardware through Simulator-Based Feedback

Large language models (LLMs) have increasingly been applied to automatic programming code generation. This task can be viewed as a language generation task that bridges natural language, human knowledge, and programming logic. However, it remains underexplored in domains that require interaction with hardware devices, such as quantum programming, where human coders write Python code that is executed on a quantum computer. To address this gap, we introduce QCoder Benchmark, an evaluation framework that assesses LLMs on quantum programming with feedback from simulated hardware devices. Our benchmark offers two key features. First, it supports evaluation using a quantum simulator environment beyond conventional Python execution, allowing feedback of domain-specific metrics such as circuit depth, execution time, and error classification, which can be used to guide better generation. Second, it incorporates human-written code submissions collected from real programming contests, enabling both quantitative comparisons and qualitative analyses of LLM outputs against human-written codes. Our experiments reveal that even advanced models like GPT-4o achieve only around 18.97% accuracy, highlighting the difficulty of the benchmark. In contrast, reasoning-based models such as o3 reach up to 78% accuracy, outperforming averaged success rates of human-written codes (39.98%). We release the QCoder Benchmark dataset and public evaluation API to support further research. (Codes and datasets are available at https://qcoder-bench.github.io/ )

cs.CL↗

arXiv2025

Rapid Modeling Architecture for Lightweight Simulator to Accelerate and Improve Decision Making for Industrial Systems

Designing industrial systems, such as building, improving, and automating distribution centers and manufacturing plants, involves critical decision-making with limited information in the early phases. The lack of information leads to less accurate designs of the systems, which are often difficult to resolve later. It is effective to use simulators to model the designed system and find out the issues early. However, the modeling time required by conventional simulators is too long to allow for rapid model creation to meet decision-making demands. In this paper, we propose a Rapid Modeling Architecture (RMA) for a lightweight industrial simulator that mitigates the modeling burden while maintaining the essential details in order to accelerate and improve decision-making. We have prototyped a simulator based on the RMA and applied it to the actual factory layout design problem. We also compared the modeling time of our simulator to that of an existing simulator, and as a result, our simulator achieved a 78.3% reduction in modeling time compared to conventional simulators.

eess.SY↗

arXiv2024

Designing Unit Ising Models for Logic Gate Simulation through Integer Linear Programming

An Ising model is defined by a quadratic objective function known as the Hamiltonian, composed of spin variables that can take values of either $-1$ or $+1$. The goal is to assign spin values to these variables in a way that minimizes the value of the Hamiltonian. Ising models are instrumental in tackling many combinatorial optimization problems, leading to significant research in developing solvers for them. Notably, D-Wave Systems has pioneered the creation of quantum annealers, programmable solvers based on quantum mechanics, for these models. This paper introduces unit Ising models, where all non-zero coefficients of linear and quadratic terms are either $-1$ or $+1$. Due to the limited resolution of quantum annealers, unit Ising models are more suitable for quantum annealers to find optimal solutions. We propose a novel design methodology for unit Ising models to simulate logic circuits computing Boolean functions through integer linear programming. By optimizing these Ising models with quantum annealers, we can compute Boolean functions and their inverses. With a fixed unit Ising model for a logic circuit, we can potentially design Application-Specific Unit Quantum Annealers (ASUQAs) for computing the inverse function, which is analogous to Application-Specific Integrated Circuits (ASICs) in digital circuitry. For instance, if we apply this technique to a multiplication circuit, we can design an ASUQA for factorization of two numbers. Our findings suggest a powerful new method for compromising the RSA cryptosystem by leveraging ASUQAs in factorization.

cs.ET↗

arXiv2023

Dual-Matrix Domain-Wall: A Novel Technique for Generating Permutations by QUBO and Ising Models with Quadratic Sizes

The Ising model is defined by an objective function using a quadratic formula of qubit variables. The problem of an Ising model aims to determine the qubit values of the variables that minimize the objective function, and many optimization problems can be reduced to this problem. In this paper, we focus on optimization problems related to permutations, where the goal is to find the optimal permutation out of the $n!$ possible permutations of $n$ elements. To represent these problems as Ising models, a commonly employed approach is to use a kernel that utilizes one-hot encoding to find any one of the $n!$ permutations as the optimal solution. However, this kernel contains a large number of quadratic terms and high absolute coefficient values. The main contribution of this paper is the introduction of a novel permutation encoding technique called dual-matrix domain-wall, which significantly reduces the number of quadratic terms and the maximum absolute coefficient values in the kernel. Surprisingly, our dual-matrix domain-wall encoding reduces the quadratic term count and maximum absolute coefficient values from $n^3-n^2$ and $2n-4$ to $6n^2-12n+4$ and $2$, respectively. We also demonstrate the applicability of our encoding technique to partial permutations and Quadratic Unconstrained Binary Optimization (QUBO) models. Furthermore, we discuss a family of permutation problems that can be efficiently implemented using Ising/QUBO models with our dual-matrix domain-wall encoding.

cs.ET↗

arXiv2020

Symmetric calorons of higher charges and their large period limits

Periodic instantons, also called calorons, are the BPS solutions to the pure Yang-Mills theories on $\mathbb{R}^3\times S^1$. It is known that the calorons interconnect with the instantons and the BPS monopoles as the ratio of their size to the period of $S^1$ varies. We give, in this paper, the action density configurations of the $SU(2)$ calorons of higher instanton charges with several platonic symmetries through the numerical Nahm transform, after the construction of the analytic Nahm data. The calorons considered are 5-caloron with octahedral symmetry, 7-caloron with icosahedral symmetry, and 4-caloron interconnecting tetrahedral and octahedral symmetries. We also consider the large period, or the instanton, limits of the Nahm data, i.e., the ADHM limits, and observe the similar spatial distributions of the action densities with the calorons.

hep-th↗

arXiv2019

Solving tiling puzzles with quantum annealing

To solve tiling puzzles, such as "pentomino" or "tetromino" puzzles, we need to find the correct solutions out of numerous combinations of rotations or piece locations. Solving this kind of combinatorial optimization problem is a very difficult problem in computational science, and quantum computing is expected to play an important role in this field. In this article, we propose a method and obtained specific formulas to find solutions for tetromino tiling puzzles using a quantum annealer. In addition, we evaluated these formulas using a simulator and using actual hardware DW2000Q.

quant-ph↗

arXiv2017

Transition between Kerr comb and stimulated Raman comb in a silica whispering gallery mode microcavity

We theoretically and experimentally investigated the transition between modulation instability and Raman gain in a small silica microcavity with a large free-spectral range (FSR), which reveals that we can selectively switch from a four-wave mixing dominant state to a stimulated Raman scattering dominant state. Both the theoretical analysis and the experiment show that a Raman-dominant region is present between transitions of Kerr combs with different free-spectral range spacings. We can obtain a stable Kerr comb and a stable Raman state selectively by changing the driving power, coupling between the cavity and the waveguide, and laser detuning. Such a controllable transition is achieved thanks to the presence of gain competition between modulation instability and Raman gain in silica whispering gallery mode microcavities.

physics.optics↗

arXiv2017

The effect on Kerr comb generation in a clockwise and counter-clockwise mode coupled microcavity

We study the impact of inherent mode coupling between clockwise (CW) and counter-clockwise (CCW) modes on Kerr comb generation in a small whispering-gallery mode microcavity. Our numerical analysis using a coupled Lugiato-Lefever equation reveals the range of the coupling strength in which a soliton pulse can be obtained in the CW direction. It also showed that CCW comb power depends on the coupling strength between the CW and CCW modes. In addition to the simulation, we conducted an experiment to confirm that the power ratio between the CW and CCW comb modes depends on the coupling strength, and the experimental results agree well with the simulation results. This study helps us to understand the relationship between CW and CCW mode coupling and Kerr comb generation, and the effect on soliton formation.

physics.optics↗

arXiv2014

Harmonic mode locking in a high-Q whispering gallery mode microcavity

A numerical and experimental study of the generation of harmonic mode locking in a silica toroid microcavity is presented. We use a generalized mean-field Lugiato-Lefever equation and solve it with the split-step Fourier method. We found that stable harmonic mode locking regime can be accessed when we reduce the input power after strong pumping even when we do not carefully adjust the wavelength detuning. This is due to the bistable nature of the nonlinear cavity system. The experiment agrees well with the numerical analysis, where we obtain low-noise Kerr comb spectrum at low longitudinal mode spacing by gradually reducing the pumping input after strong pumping. This finding clarifies the procedure for generating harmonic mode locking in such high-Q microcavity systems.

physics.optics↗

arXiv2013

Fabrication of whispering gallery mode cavity using crystal growth

We developed a new method for fabricating crystalline whispering gallery mode cavities based on laser-heated pedestal growth. We fabricated sapphire cavities and obtained a Q factor of 16000 with a cavity whose diameter was about 240 um. We showed numerically that the cross-sectional shape of the cavity is sensitive to the cavity Q, and we controlled it successfully by changing the growth condition in the molten zone, without significantly degrading the crystal structure.

physics.optics↗

arXiv2012

Polygonal silica toroidal microcavity for controlled optical coupling

We fabricated polygonal silica toroidal microcavities to achieve stable mechanical coupling with an evanescent coupler such as a tapered fiber. The polygonal cavity was fabricated by using a combination of isotropic etching, anisotropic etching and laser reflow. It offers both high and low coupling efficiencies with the cavity mode even when the coupler is in contact with the cavity, which offers the possibility of taking the device outside the laboratory. A numerical simulation showed that an octagonal silica toroidal microcavity had an optical quality factor of 8.8\times10^6.

physics.optics↗