arXiv subjects

Motoki Asano

Publications and source records attributed to Motoki Asano.

At least 19 recordsLinked to original sources

arXiv2026

Phase control of magnon-phonon coupling via magnetic field

We study the phase of the coupling between magnons and surface acoustic wave (SAW) phonons in magnetic thin films. The coupling constant changes from a real to a complex number as the external magnetic field is reduced. Below a transition field, the imaginary coupling constant allows SAW phonons to couple to overdamped magnons whose resonance frequency is close to zero and far from the SAW resonance. The strength of the imaginary coupling constant and the magnitude of the transition field both scale with magnetic damping. We find the coupling produces a broad, pronounced minimum in the SAW transmittance spectrum near zero magnetic field in a Ni/Ru/Ni synthetic antiferromagnet with large magnetic damping. These results demonstrate that the phase of the complex magnon-phonon coupling constant can be tuned via magnetic field in strongly damped magnets, offering a platform to explore novel regimes of magnon-phonon interactions.

cond-mat.mes-hall↗

arXiv2026

Nonreciprocal phonon propagation via spatially asymmetric magnon-phonon coupling

Nonreciprocal propagation of surface acoustic waves (SAWs) based on the spatial asymmetry of magnon-phonon coupling is demonstrated. This nonreciprocity is enabled by an acoustic wavelength scale thick magnetic layer formed under a thin piezoelectric film. In this configuration, magnon modes activated by dipole-dipole interactions are localized near either the top or bottom interface depending on the propagation direction of the SAW. As a result, the spatial overlap between interfacial magnon and surface phonon modes is expected to become direction dependent, in a manner that leads to distinct unidirectional propagation of SAWs. Notably, the resulting nonreciprocity reaches the highest level among those reported for SAW devices based on a single magnetic layer. This finding will establish a new strategy of nonreciprocal acoustic propagation in a structurally simple magnomechanical device.

cond-mat.mes-hall↗

arXiv2026

Optomechanical parametric control of mid-infrared photons via molecular vibrational polariton

Controlling mid-infrared (MIR) photons using well-developed telecom photonic platforms would enable new functionalities in molecular and quantum photonics. However, establishing efficient interactions between MIR and telecom photons remains challenging due to their large spectral separation and weak nonlinear coupling. Here, we demonstrate optomechanical control of MIR photons mediated by vibrational polaritons, enabling photon-photon interaction between MIR and telecom fields across distant spectral regions. Using a Fabry-P\'erot cavity incorporating a vibrationally active polymer, we observe telecom-driven dissipation enhancement of MIR photons at 9.5 $\mu$m with a modulation depth of 1% under a 4 mW pump. The linear power dependence, mixing-ratio dependence, and detuning response consistently indicate a MIR and telecom photon-photon conversion enabled by strong light-matter coupling. This approach establishes a polaritonic optomechanical platform for bridging disparate spectral regimes and provides a dissipation-engineered route toward hybrid MIR photonics and quantum transduction.

physics.optics↗

arXiv2026

Magnetoelastic Waves in Ferromagnetic Thin Films Mediated by Dipolar Interactions

Magnetoelastic coupling mediated by magnetic dipolar interactions is theoretically investigated in ferromagnetic thin films under an in-plane magnetic field. We develop a theoretical description that incorporates dipolar fields derived from Maxwell's equations in the presence of elastic deformations. The resulting coupled equations of motion predict hybridization between magnetostatic and Lamb waves. Numerical calculations for a yttrium iron garnet (YIG) film reveal anti-crossings in the dispersion relations, with hybridization gaps ranging from $0.1$ to several MHz.

cond-mat.mtrl-sci↗

arXiv2026

Topological phase dynamics described by overtone-synthesized classical and quantum Adler equations

The Adler equation is a well-known one-dimensional model describing phase locking and synchronization. Motivated by recent experiments using optomechanical oscillators, we extend the model to include overtone-synthesized sinusoidal coupling with adiabatic temporal modulation. This extension gives rise to unique topological features such as winding-number quantization, discontinuous phase-slip transitions, and hysteretic and non-reciprocal phase dynamics. We further extend the analysis to the quantum regime, where we find a counterintuitive result: the breakdown of winding-number quantization. This arises from the superposition of different winding-number states in a closed-space Thouless pump. Moreover, hysteretic dynamics, once eliminated in quantum adiabatic approximation, is recovered in non-adiabatic calculations, as the superposition of two Floquet states with different PT eigenvalues becomes the quantum counterpart of phase trajectory.

quant-ph↗

arXiv2026

Optically tunable nonlinear mechanical damping in an optomechanical resonator

We theoretically propose and experimentally demonstrate optically tunable nonlinear mechanical damping in a cavity optomechanical system utilizing a partly resolved sideband regime. Optomechanical coupling provides a delayed nonlinear backaction to the mechanical modes, resulting in nonlinear mechanical damping. This optically induced nonlinear damping is observed in the frequency and time domains, and we show using both theory and experiment that it can be tuned via laser detuning. Specifically, we observe positive nonlinear damping in the blue-detuned regime and negative nonlinear damping in the red-detuned regime. We also observe optically mediated cross-nonlinear damping between two mechanical modes: the amplitude of one mode modulates the damping of the other. The presented results show a tunable scheme of nonlinear mechanical damping that will be applicable to various non-trivial systems, governed by nonlinear, nonequilibrium, and non-Hermitian phenomena.

cond-mat.mes-hall↗

arXiv2025

On-chip magnon polaron generation in mode-matched cavity magnomechanics

Generation of magnon polarons, which are hybridized states resulting from strong magnon-phonon coupling, is a key to enabling coherent manipulation in acoustic and spintronic devices. However, the conventional device configuration, a magnetic thin film on a thick piezoelectric layer, often has difficulty achieving a large magnon-phonon coupling due to a very small spatial mode overlap. Here, we demonstrate generation of magnon polarons by using a mode-matched on-chip magnomechanical system. A configuration with a thin piezoelectric film on a magnetic layer several micrometers thick was found to sustain deeply distributed magnon modes that enable magnetoelastic coupling to phonons over almost the entire mode volume. The enhanced spatial mode overlap generated magnon polarons whose spectra showed distinct avoided crossing. This magnomechanical system will facilitate utilization of coherent magnon-phonon conversion and their hybrid states in functional phononic devices.

cond-mat.mes-hall↗

arXiv2025

Synthesized Kuramoto potential via optomechanical Floquet engineering

Synchronization is a ubiquitous scientific phenomenon in various physical systems. Here, we examine the feasibility of generating multistable and dynamically tunable synchronization by using the technique of Floquet engineering. Applying a periodically modulated laser light to optomechanical oscillators allows for stable and precise control of oscillator couplings. This enables us not only to explore the physics of quantized integer and fractional phase slips but also synthesize multioctave synchronizations of mechanical oscillators that exhibit tailorable multistability. Furthermore, the dynamically manipulated synchronizations lead to an exotic topology wherein the phase trajectories have a nontrivial winding number and giant non-reciprocity. This scheme could help to elucidate the dynamics of complicated oscillator networks like biological systems and to mimic their highly efficient information processing.

cond-mat.mes-hall↗

arXiv2024

Near-field optomechanical transduction enhanced by Raman gain

Raman-gain-enhanced near-field optomechanical transduction between a movable optical cavity and SiN-membrane resonator is demonstrated. The Raman gain compensates for the intrinsic loss of the cavity and amplifies the optomechanical transduction, through which the membrane vibration is sensed using a high-Q whispering-gallery-mode optical cavity evanescently. The optical Q of the cavity resonance is improved with respect to the optical pump power, which results in an increase in the optomechanically transduced vibration signals of the mechanical resonator. Our near-field optomechanical coupling approach with optical gain realizes highly sensitive displacement measurement in nano- and micro-mechanical resonators consisting of arbitrary materials and structures.

physics.optics↗

arXiv2024

Cavity optomechanical liquid level meter using a twin-microbottle resonator

Cavity optomechanical devices can be made to have good compatibility with optical fiber technology by utilizing fiber-based waveguides and cavities and can be used in high-performance optical sensor applications. Such optomechanical microsensors have a great potential for exploring the properties of liquids, such as density, viscosity, and masses of included nanoparticles. However, as yet, there is no cavity optomechanical architecture that can be used to sense the liquid's shape, e.g., liquid level. In this paper, we report a demonstration of a liquid-level meter using a twin-microbottle resonator that can make measurements at arbitrary positions and depths in the liquid. The twin-microbottle resonator has a maximum diameter of 68 $\mu$m and length of 800 $\mu$m. By immersing one part of it in water and keeping the other part in air, the mechanical radial breathing mode can be read out sensitively while maintaining a high optical quality factor of the optical whispering gallery mode regardless of the water immersion. This high mechanical displacement sensitivity provides a frequency resolution that is high enough to measure the mechanical frequency shift due to the water immersion and resolves the water level to 2.6$\pm$0.9 pm. This unique liquid-level meter based on a highly sensitive cavity optomechanical setup can be used to detect tiny fluctuations of various air-liquid and liquid-liquid interfaces.

physics.optics↗

arXiv2023

Magnon-phonon coupling of synthetic antiferromagnets in a surface acoustic wave cavity resonator

We use a surface acoustic wave (SAW) cavity resonator to study the coupling of acoustic magnons in a synthetic antiferromagnet (SAF) and the phonons carried by SAWs. The SAF is composed of a CoFeB/Ru/CoFeB trilayer and the scattering matrix of the SAW resonator is studied to assess the coupling. We find that the spectral linewidth of the SAW resonator is modulated when the frequency of the excited magnons approaches the SAW resonance frequency. Moreover, the linewidth modulation varies with the magnitude and orientation of the external magnetic field. Such change in the spectral linewidth can be well reproduced using macrospin-like model calculations. From the model analyses, we estimate the magnon-phonon coupling strength to be $\sim$15.6 MHz at a SAW resonance frequency of 1.8 GHz: the corresponding magnomechanical cooperativity is $\sim$0.66. As the spectral shape hardly changes in a CoFeB single layer reference sample under the same experimental condition, these results show that SAF provides an ideal platform to study magnon-phonon coupling in a SAW cavity resonator.

cond-mat.mes-hall↗

arXiv2023

A fiber-type optomechanical array using high-Q microbottle resonators

We demonstrate a fiber-type optomechanical array consisting of elastically interconnected silica microbottle resonators with high-Q optical and mechanical modes. In total, fifty optomechanical resonators fabricated by fine glass processing are uniformly arrayed on a silica fiber. Evanescent coupling of a tapered optical fiber to an arbitrary resonator allows for highly sensitive readout and efficient actuation of mechanical motion at an arbitrary position in the array. Phonon propagation through the fifty microbottles is achieved by both linearly and parametrically driving a mechanical mode at one end and by detecting it at the other end. This optomechanical array is scalable, tunable, and lithography-free and can be extended to fiber-based sensory applications with structural flexibility and operability in various environments.

cond-mat.mes-hall↗

arXiv2023

Cavity magnomechanical coupling with coupled magnon modes in a synthetic antiferromagnet

On-chip cavity magnomechanics is an emerging field exploring acoustic and magnonic functionalities of various ferromagnetic materials and structures using strongly confined phonons. It is expected that such cavity magnomechanics can be extended to multilayer ferromagnets, especially synthetic antiferromagnets (SAFs) that exhibit zero net magnetization through interlayer exchange coupling. However, the conventional theoretical framework for a single ferromagnet cannot be used directly because of the antiferromagnetic magnetization dynamics associated with the interlayer exchange coupling. In this paper, we theoretically investigate phonon-magnon coupling with a three-layer SAF. Our formulation of the phonon-magnon coupling constants reveals that the acoustic (optical) magnon mode dominantly couples to the cavity phonon when the magnetization angles in the two ferromagnetic layers are antiparallel (orthogonal). Moreover, numerical calculations including the effects of dipole-dipole interactions and in-plane uniaxial magnetic anisotropy allow us to predict phonon frequency shifts and linewidth broadening that can be detected in experiments. These theoretical insights would greatly help us to make a strategy for bringing the system into the strong coupling regime and to devise novel control protocols in analogy to cavity quantum electrodynamics and cavity optomechanics.

cond-mat.mes-hall↗

arXiv2023

Quadrature skyrmions in two-dimensionally arrayed parametric resonators

Skyrmions are topological solitons in two-dimensional systems and have been observed in various physical systems. Generating and controlling skyrmions in artificial resonator arrays lead to novel acoustic, photonic, and electric devices, but it is a challenge to implement a vector variable with the chiral exchange interaction. Here, we propose to use quadrature variables, where their parametric coupling enables skyrmions to be stabilized. A finite-element simulation indicates that a acoustic skyrmion would exist in a realistic structure consisting of a piezoelectric membrane array.

cond-mat.mes-hall↗

arXiv2023

Cavity optomechanical mass sensor in water with sub-femtogram resolution

Sub-femtogram resolution of an in-liquid cavity optomechanical mass sensor based on the twin-microbottle glass resonator is demonstrated. An evaluation of the frequency stability using an optomechanical phase-locked loop reveals that this cavity optomechanical sensor has the highest mass resolution of $(7.0\times2.0)\times 10^{-16}$ g in water, which is four orders of magnitude better than that in our first-generation setup [Sci. Adv. 8, eabq2502 (2022)]. This highly sensitive mass sensor provides a free-access optomechanical probe in liquid and could thus be extended to a wide variety of in-situ chemical and biological metrology applications.

physics.optics↗

arXiv2022

Phononic-crystal cavity magnomechanics

Establishing a way to control magnetic dynamics and elementary excitations (magnons) is crucial to fundamental physics and the search for novel phenomena and functions in magnetic solid-state systems. Electromagnetic waves have been developed as means of driving and sensing in magnonic and spintronics devices used in magnetic spectroscopy, non-volatile memory, and information processors. However, their millimeter-scale wavelengths and undesired cross-talk have limited operation efficiency and made individual control of densely integrated magnetic systems difficult. Here, we utilize acoustic waves (phonons) to control magnetic dynamics in a miniaturized phononic crystal micro-cavity and waveguide architecture. We demonstrate acoustic pumping of localized ferromagnetic magnons, where their back-action allows dynamic and mode-dependent modulation of phononic cavity resonances. The phononic crystal platform enables spatial driving, control and read-out of tiny magnetic states and provides a means of tuning acoustic vibrations with magnons. This alternative technology enhances the usefulness of magnons and phonons for advanced sensing, communications and computation architectures that perform transduction, processing, and storage of classical and quantum information.

cond-mat.mes-hall↗

arXiv2022

Free-space optomechanical liquid probes using a twin-microbottle resonator

Cavity optomechanics provides high-performance sensor technology, and the scheme is also applicable to liquid samples for biological and rheological applications. However, previously reported methods using fluidic capillary channels and liquid droplets are based on fixed-by-design structures and therefore do not allow an active free-space approach to the samples. Here, we demonstrate an alternate technique using a probe-based architecture with a twin-microbottle resonator. The probe consists of two microbottle optomechanical resonators, where one bottle (for detection) is immersed in liquid and the other bottle (for readout) is placed in air, which retains excellent detection performance through the high optical-Q (~107) of the readout bottle. The scheme allows the detection of thermomechanical motion of the detection bottle as well as its optomechanical sideband drive. This technique could lead to in-situ metrology at the target location in arbitrary media, and could be extended to ultrasensitive biochips and rheometers.

physics.optics↗

arXiv2022

A Kuramoto Network in a Single Nonlinear Microelectromechanical Device

This work presents a frequency multiplexed 3-limit cycles network in a multimode microelectromechanical nonlinear resonator. The network is composed of libration limit cycles and behaves in an analogous manner to a phase oscillator network. The libration limit cycles, being of low frequency, interact through the stress tuning of the resonator, and result in an all-to-all coupling that can be described by a Kuramoto model. Beyond the typically present cubic nonlinearity the modes in question do not require any special frequency ratios. Thus an interconnect free Kuramoto network is established within a single physical device without the need for electrical or optical coupling mechanisms between the individual elements.

physics.app-ph↗