arXiv subjects

Keita Matsumoto

Publications and source records attributed to Keita Matsumoto.

8 recordsLinked to original sources

arXiv2025

A Practical Open-Source Software Stack for a Cloud-Based Quantum Computing System

Since the late 2010s, quantum computers have become commercially available, and the number of services that users can run remotely via cloud servers is increasing. In Japan, several domestic superconducting quantum computing systems, including our own, began operation in 2023. However, the design of quantum computing systems, especially in the most critical areas near quantum computers, remains largely undisclosed, creating a significant barrier to entry into the quantum computing field. If this situation continues, progress toward standardization, which is essential for guiding quantum computer development, will stall, and it will be difficult to develop a practical quantum computing system that can perform calculations on a supercomputer scale. To address this issue, we propose Open Quantum Toolchain for OPerators and USers (OQTOPUS), a full-stack quantum computing system developed from research with real quantum computers. OQTOPUS is one of the world's largest open-source software projects, covering operational software from cloud-based execution environment construction to system operation. Furthermore, to perform quantum computing effectively and efficiently, it implements key features, such as transpilers, multiprogramming, and error mitigation, in an area as close as possible to a quantum computer, an area that system vendors rarely disclose. Finally, this study presents experimental results of applying OQTOPUS to a real quantum computer. OQTOPUS is publicly available on GitHub and will notably lower the barrier to entry into the quantum computing field, contributing to the formation of a quantum computing developer community through open discussion.

quant-ph↗

arXiv2024

Sub-millimeter propagation of antiferromagnetic magnons via magnon-photon coupling

For the realization of magnon-based current-free technologies, referred to as magnonics, all-optical control of magnons is an important technique for both fundamental research and practical applications. Magnon-polariton is a coupled state of magnon and photon in a magnetic medium, expected to exhibit magnon-like controllability and photon-like high-speed propagation. While recent studies have observed magnon-polaritons as modulation of incident terahertz waves, the influence of magnon-photon coupling on magnon propagation properties remains unexplored. This study aimed to observe the spatiotemporal dynamics of coherent magnon-polaritons through time-resolved imaging measurements. BiFeO$_3$ was selected as the sample due to its anticipated strong coupling between magnons and photons. The observed dynamics suggest that antiferromagnetic magnons can propagate over long distances, up to hundreds of micrometers, through strong coupling with photons. These results enhance our understanding of the optical control of magnonic systems, thereby paving the way for terahertz opto-magnonics.

cond-mat.mtrl-sci↗

arXiv2023

Sublattice-selective inverse Faraday effect in ferrimagnetic rare-earth iron garnet

We performed time-resolved pump--probe measurements using rare-earth iron garnet \ce{Gd3/2Yb1/2BiFe5O12} as a two-sublattice ferrimagnet. We measured the initial phases of the magnetic resonance modes below and above the magnetization compensation temperature to clarify the sublattice selectivity of the inverse Faraday effect in ferrimagnets. A comparison of the time evolution of magnetization estimated using the equations of motion revealed that the inverse Faraday effect occurring in ferrimagnetic materials has sublattice selectivity. This is in striking contrast to antiferromagnets, in which the inverse Faraday effect acts on each sublattice identically. The initial phase analysis can be applied to other ferrimagnets with compensation temperatures.

cond-mat.mtrl-sci↗

arXiv2021

Fast acquisition of spin-wave dispersion by compressed sensing

For the realization of magnonic devices, spin-wave dispersions need to be identified. Recently, the time-resolved pump-probe imaging method combined with the Fourier transform was demonstrated for obtaining the dispersions in the lower-wavenumber regime. However, the measurement takes a long time when the sampling rate is sufficiently high. Here, we demonstrated the fast acquisition of spin-wave dispersions by using the compressed sensing technique. Further, we quantitatively evaluated the consistency of the results. Our results can be applied to other various pump-probe measurements, such as observations based on the electro-optical effects.

physics.optics↗

arXiv2020

Selective imaging of terahertz electric field of phonon-polariton in LiNbO$_3$

Coherent phonon-polaritons have attracted a considerable amount of interest owing to their relevance to nonlinear optics and terahertz (THz)-wave emissions. Therefore, it is important to analyze the THz electric-fields of phonon-polaritons. However, in the majority of previous measurements, only a single component of the THz electric field was detected. In this paper, we demonstrate that pump-probe electro-optical imaging measurements using the Stokes parameters of probe polarization enable the phase-resolved selective detection of THz electric-field components that are associated with the phonon-polariton. We experimentally distinguish the mode profiles of ordinary and extraordinary phonon-polaritons, and clarify the excitation mechanism as optical rectification. These results are explained by numerical calculations of Maxwell equations for the THz electric field. The technique of selectively observing the THz electric field components may be useful for designing efficient THz-wave emitters.

physics.optics↗

arXiv2020

Observation of evanescent spin waves in the magnetic dipole regime

We observed spin-wave transmission through an air gap that works as a prohibited region. The spin waves were excited by circularly polarized pump pulses via the inverse Faraday effect, and their spatial propagation was detected through the Faraday effect of probe pulses using a pump-probe imaging technique. The experimentally observed spin-wave transmission was reproduced using numerical calculations with a Green's function method and micromagnetic simulation. We found that the amplitude of the spin waves decays exponentially in the air gap, which indicates the existence of evanescent spin waves in the magnetic dipole regime. This finding will pave the way for controllable amplitudes and phases of spin waves propagating through an artificial magnonic crystal.

physics.optics↗

arXiv2020

Ultrafast Light-driven Simultaneous Excitation of Coherent Terahertz Magnons and Phonons in Multiferroic BiFeO$_3$

The ultrafast switching of magnetization in multiferroic materials by a femtosecond laser could provide various advantages in photonics and magnonics. An efficient approach to control the light matter interaction is the modulation of ultrafast coherent magnons and phonons in the high frequency range. Spontaneous Raman and infrared spectra reveal the excitation of magnons and optical phonons in multiferroic BiFeO3 in the sub few terahertz range. However, coherent control of such quasiparticles has not been achieved yet. In this study, we demonstrate that linearly polarized laser pulses simultaneously excite coherent magnons out of plane and in plane cyclone modes and optical phonon E mode in BiFeO3. Experimental results in conjugation with phenomenological theory, by considering three uniformly distributed magnetic domains reveal that impulsive stimulated Raman scattering is responsible for the generation of coherent magnons and phonons in BiFeO3. The observation of these terahertz magnon and optical phonon modes paves the way for the development of ultrafast magneto electro optical devices.

physics.optics↗

arXiv2018

Optical determination of the exchange stiffness constant in an iron garnet

Brillouin light scattering measurements were performed in the backscattering geometry on a Bi-substituted rare earth iron garnet. We observed two different peaks, one attributed to a surface spin wave in the dipole-exchange regime. The other is referred to as a backscattering magnon mode, because the incident light in this case is scattered backward by exchange-dominated spin wave inside the material. We propose a method to estimate the exchange stiffness constant from the frequency of the backscattering magnon mode. The obtained value is comparable with the previously reported values for Y$ _3 $Fe$ _5 $O$ _{12} $.

physics.optics↗