arXiv subjects

Y. Sekiguchi

Publications and source records attributed to Y. Sekiguchi.

5 recordsLinked to original sources

arXiv2026

Scalable on-chip integration of diamond color centers for cryogenic quantum photonics

Chip integration of quantum emitters is a crucial milestone for scalable quantum photonic information processing. Among optically active defect centers for quantum photonics, diamond color centers are promising because of their long spin coherence times and high photon emission rates. However, for a coherent-photon emission, they typically require a cryogenic environment to protect optical coherence from thermal phonons, which makes chip integration challenging. In this paper, we develop a chip-integrated diamond photonic crystal cavity embedding an ensemble of nitrogen-vacancy (NV) centers. We confirm cryogenic operation by observing Purcell enhancement of NV-center emission via an edge-coupled optical fiber. This result demonstrates successful integration of diamond color centers, a photonic crystal cavity, and an optical waveguide-fiber package, representing a key step toward scalable diamond-based quantum communication platforms.

quant-ph↗

arXiv2025

High-Throughput Mapping of Magnetic Properties via the on-the-fly XMCD spectroscopy in a Combinatorial Fe-Co-Ni Film

High-throughput X-ray magnetic circular dichroism (XMCD) spectroscopy was conducted on Fe-Co-Ni compositionally graded films to systematically analyze the variation of magnetic properties as a function of composition. On-the-fly XMCD measurement enabled rapid spectral acquisition. Measurement time was reduced approximately tenfold compared to conventional stepwise methods, while maintaining high precision. The obtained XMCD spectra were processed using the Savitzky-Golay denoising technique, and element-specific magnetic properties were extracted using XMCD sum rules. By mapping the orbital and spin magnetic moments across the composition gradient, we identified key regions exhibiting enhanced soft magnetic properties. This study demonstrates the effectiveness of high-throughput synchrotron-based spectroscopy for accelerating materials discovery and optimizing functional magnetic materials.

cond-mat.mtrl-sci↗

arXiv2025

The Ladder and Readout Cables of Intermediate Silicon Strip Detector for sPHENIX

A new silicon-strip-type detector was developed for precise charged-particle tracking in the central rapidity region of heavy ion collisions. A new detector and collaboration at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is sPHENIX, which is a major upgrade of the PHENIX detector. The intermediate tracker (INTT) is part of the advanced tracking system of the sPHENIX detector complex together with a CMOS monolithic-active-pixel-sensor based silicon-pixel vertex detector, a time-projection chamber, and a micromegas-based detector. The INTT detector is barrel shaped and comprises 56 silicon ladders. Two different types of strip sensors of 78~$\mu m$ pitch and 320~$\mu m$ thick are mounted on each half of a silicon ladder. Each strip sensor is segmented into 8$\times$2 and 5$\times$2 blocks with lengths of 16 and 20 mm. Strips are read out with a silicon strip-readout (FPHX) chip. In order to transmit massive data from the FPHX to the down stream readout electronics card (ROC), a series of long and high speed readout cables were developed. This document focuses on the silicon ladder, the readout cables, and the ROC of the INTT. The radiation hardness is studied for some parts of the INTT devices in the last part of this document, since the INTT employed some materials from the technology frontier of the industry whose radiation hardness is not necessarily well known.

physics.ins-det↗

arXiv2020

Design and Performance of a Silicon Tungsten Calorimeter Prototype Module and the Associated Readout

We describe the details of a silicon-tungsten prototype electromagnetic calorimeter module and associated readout electronics. Detector performance for this prototype has been measured in test beam experiments at the CERN PS and SPS accelerator facilities in 2015/16. The results are compared to those in Monte Carlo Geant4 simulations. This is the first real-world demonstration of the performance of a custom ASIC designed for fast, lower-power, high-granularity applications.

physics.ins-det↗

arXiv2007

Magnetohydrodynamics of Neutrino-Cooled Accretion Tori around a Rotating Black Hole in General Relativity

We present our first numerical results of axisymmetric magnetohydrodynamic simulations for neutrino-cooled accretion tori around rotating black holes in general relativity. We consider tori of mass $\sim 0.1$--0.4$M_{\odot}$ around a black hole of mass $M=4M_{\odot}$ and spin $a=0$--$0.9M$; such systems are candidates for the central engines of gamma-ray bursts (GRBs) formed after the collapse of massive rotating stellar cores and the merger of a black hole and a neutron star. In this paper, we consider the short-term evolution of a torus for a duration of $\approx 60$ ms, focusing on short-hard GRBs. Simulations were performed with a plausible microphysical equation of state that takes into account neutronization, the nuclear statistical equilibrium of a gas of free nucleons and $α$-particles, black body radiation, and a relativistic Fermi gas (neutrinos, electrons, and positrons). Neutrino-emission processes, such as $e^{\pm}$ capture onto free nucleons, $e^{\pm}$ pair annihilation, plasmon decay, and nucleon-nucleon bremsstrahlung are taken into account as cooling processes. Magnetic braking and the magnetorotational instability in the accretion tori play a role in angular momentum redistribution, which causes turbulent motion, resultant shock heating, and mass accretion onto the black hole. The mass accretion rate is found to be $\dot M_* \sim 1$--$10 M_{\odot}$/s, and the shock heating increases the temperature to $\sim 10^{11}$ K. This results in a maximum neutrino emission rate of $L_ν=$ several $\times 10^{53}$ ergs/s and a conversion efficiency $L_ν/\dot M_* c^2$ on the order of a few percent for tori with mass $M_{\rm t} \approx 0.1$--0.4$M_{\odot}$ and for moderately high black hole spins.

astro-ph↗