Koji Usami
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View article: Uni-Traveling-Carrier Photodiode Based on MoS2/GaN van der Waals Heterojunction for High-Speed Visible-Light Detection
Uni-Traveling-Carrier Photodiode Based on MoS2/GaN van der Waals Heterojunction for High-Speed Visible-Light Detection Open
Uni-traveling-carrier photodiodes (UTC-PDs), which utilize only electrons as the active carriers, have become indispensable in high-speed optoelectronics due to their unique capabilities, such as high saturation power and broad bandwidth. …
View article: Magnon-exciton proximity coupling at a van der Waals heterointerface
Magnon-exciton proximity coupling at a van der Waals heterointerface Open
Spin and photonic systems are at the heart of modern information devices and emerging quantum technologies. An interplay between electron-hole pairs (excitons) in semiconductors and collective spin excitations (magnons) in magnetic crystal…
View article: Heating-free, room-temperature operation of a radiofrequency-to-light signal transducer with a membrane oscillator and a built-in metasurface mirror
Heating-free, room-temperature operation of a radiofrequency-to-light signal transducer with a membrane oscillator and a built-in metasurface mirror Open
We present an electro-mechano-optical radiofrequency (rf)-to-light signal transducer robust against laser heating and thus operational at room temperature. A metal-free, low-loss metasurface mirror and an aluminum electrode made separately…
View article: Optical polarimetric measurement of surface acoustic waves
Optical polarimetric measurement of surface acoustic waves Open
A surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology for transducing, sensing, and processing various signals. Optical measurement of the SAW provides valuable information since the ampl…
View article: Cavity Magnonics
Cavity Magnonics Open
Cavity magnonics deals with the interaction of magnons - elementary
excitations in magnetic materials - and confined electromagnetic fields. We
introduce the basic physics and review the experimental and theoretical
progress of this young …
View article: Optical polarimetric imaging of surface acoustic waves
Optical polarimetric imaging of surface acoustic waves Open
Surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology, for transducing, sensing and processing various signals. Optical imaging of SAW provides valuable information since the amplitude and …
View article: Dissipation-Based Quantum Sensing of Magnons with a Superconducting Qubit
Dissipation-Based Quantum Sensing of Magnons with a Superconducting Qubit Open
Hybrid quantum devices expand the tools and techniques available for quantum sensing in various fields. Here, we experimentally demonstrate quantum sensing of a steady-state magnon population in a magnetostatic mode of a ferrimagnetic crys…
View article: Proximity-mediated magnon-exciton coupling at a van der Waals heterointerface
Proximity-mediated magnon-exciton coupling at a van der Waals heterointerface Open
Coupling between heterogeneous physical systems holds great promises to leverage their individual assets. For example, low-dissipative spin ensembles are combined with well-controlled electric and phononic devices for spintronics, or with …
View article: Radio-frequency-to-optical conversion using acoustic and optical whispering-gallery modes
Radio-frequency-to-optical conversion using acoustic and optical whispering-gallery modes Open
Whispering gallery modes (WGMs), circulating modes near the surface of a\nspheroidal material, have been known to exhibit high quality factors for both\nacoustic and electromagnetic waves. Here, we report an electro-optomechanical\nsystem,…
View article: Helicity-Changing Brillouin Light Scattering by Magnons in a Ferromagnetic Crystal
Helicity-Changing Brillouin Light Scattering by Magnons in a Ferromagnetic Crystal Open
Brillouin light scattering in ferromagnetic materials usually involves one magnon and two photons and their total angular momentum is conserved. Here, we experimentally demonstrate the presence of a helicity-changing two-magnon Brillouin l…
View article: Optical heterodyne imaging of magnetostatic modes in one-dimensional magnonic crystals
Optical heterodyne imaging of magnetostatic modes in one-dimensional magnonic crystals Open
We demonstrate a real-space imaging of a heterodyne signal of light that is produced as a result of the Brillouin light scattering by coherently driven magnons in magnetostatic modes. With this imaging technique, we characterize surface ma…
View article: Helicity-Changing Brillouin Light Scattering in a Ferromagnetic Crystal
Helicity-Changing Brillouin Light Scattering in a Ferromagnetic Crystal Open
Brillouin light scattering in ferromagnetic materials usually involves one magnon and two photons and their total angular momentum is conserved. Here, we experimentally demonstrate the presence of a helicity-changing two-magnon Brillouin l…
View article: Brillouin Light Scattering by Magnetic Quasivortices in Cavity Optomagnonics
Brillouin Light Scattering by Magnetic Quasivortices in Cavity Optomagnonics Open
A ferromagnetic sphere can support optical vortices in the form of whispering gallery modes and magnetic quasivortices in the form of magnetostatic modes with nontrivial spin textures. These vortices can be characterized by their orbital a…
View article: Electro-mechano-optical detection of nuclear magnetic resonance
Electro-mechano-optical detection of nuclear magnetic resonance Open
Signal reception of nuclear magnetic resonance (NMR) usually relies on\nelectrical amplification of the electromotive force caused by nuclear\ninduction. Here, we report up-conversion of a radio-frequency NMR signal to an\noptical regime u…
View article: Nonclassical Photon Number Distribution in a Superconducting Cavity under a Squeezed Drive
Nonclassical Photon Number Distribution in a Superconducting Cavity under a Squeezed Drive Open
A superconducting qubit in the strong dispersive regime of circuit quantum electrodynamics is a powerful probe for microwave photons in a cavity mode. In this regime, a qubit excitation spectrum is split into multiple peaks, with each peak…
View article: Electro-mechano-optical NMR detection
Electro-mechano-optical NMR detection Open
Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime usin…
View article: Cavity optomechanics with surface acoustic waves
Cavity optomechanics with surface acoustic waves Open
We report a development of an electro-optomechanical system based on a surface acoustic wave (SAW), where a piezoelectric material with a large optoelastic susceptibility is used for the coupling of both a radio wave and optical light to t…
View article: Nonclassical photon number distribution in a superconducting cavity under a squeezed drive
Nonclassical photon number distribution in a superconducting cavity under a squeezed drive Open
A superconducting qubit in the strong dispersive regime of a circuit quantum electrodynamics system is a powerful probe for microwave photons in a cavity mode. In this regime, a qubit spectrum is split into multiple peaks, with each peak c…
View article: Ground state cooling of a quantum electromechanical system with a silicon nitride membrane in a 3D loop-gap cavity
Ground state cooling of a quantum electromechanical system with a silicon nitride membrane in a 3D loop-gap cavity Open
Cavity electro-(opto-)mechanics gives us a quantum tool to access mechanical modes in a massive object. Here we develop a quantum electromechanical system in which a vibrational mode of a SiN _x membrane are coupled to a three-dimensional …
View article: Quantum magnonics: The magnon meets the superconducting qubit
Quantum magnonics: The magnon meets the superconducting qubit Open
The techniques of microwave quantum optics are applied to collective spin excitations in a macroscopic sphere of a ferromagnetic insulator. We demonstrate, in the single-magnon limit, strong coupling between a magnetostatic mode in the sph…
View article: Cavity Optomagnonics with Spin-Orbit Coupled Photons
Cavity Optomagnonics with Spin-Orbit Coupled Photons Open
We experimentally implement a system of cavity optomagnonics, where a sphere of ferromagnetic material supports whispering gallery modes (WGMs) for photons and the magnetostatic mode for magnons. We observe pronounced nonreciprocity and as…
View article: Bidirectional conversion between microwave and light via ferromagnetic magnons
Bidirectional conversion between microwave and light via ferromagnetic magnons Open
Coherent conversion of microwave and optical photons in the single-quantum level can significantly expand our ability to process signals in various fields. Efficient up-conversion of a feeble signal in the microwave domain to the optical d…
View article: Strong coupling in multimode quantum electromechanics
Strong coupling in multimode quantum electromechanics Open
Cavity electro-(opto-)mechanics allows us to access not only single isolated but also multiple mechanical modes in a massive object. Here we develop a multi-mode electromechanical system in which a several membrane vibrational modes are co…