arXiv subjects

Hiroshi Yamaguchi

Publications and source records attributed to Hiroshi Yamaguchi.

At least 55 records · Page 3Linked to original sources

arXiv2018

Pulse-width modulated oscillations in a nonlinear resonator under two-tone driving as a means for MEMS sensor readout

A MEMS Duffing resonator is driven by two adjacent frequency tones into the nonlinear regime. We show that if the two-tone drive is applied at a frequency where a bistable response of the nonlinear oscillator exists, then the system output will be modulated by a relaxation cycle caused by periodically jumping between the two solution-branches of the bistable response. Although the jumps are caused by the beating of the drives, the existence and period of this relaxation or hysteresis cycle is not solely dictated by the beat frequency between the two driving tones, but also by their amplitude and detuning with respect to the device resonance frequency. We equally demonstrate how the period of the cycles can be tuned via added tension in the device and how these oscillations can be used as a means of sensitive pulse-width modulated (PWM) readout of MEMS sensors.

cond-mat.mes-hall↗

arXiv2018

Electrostatically induced phononic crystal

The possibility of realizing an electrostatically induced phononic crystal is investigated numerically in an acoustic waveguide based on a graphene sheet that is suspended over periodically arrayed electrodes. The application of dc voltage to these electrodes exerts electrostatic force on the graphene and this results in the periodic formation of stress in the waveguide structure in a non-invasive way, unlike the cases with mass loading and air holes. This non-invasive scheme enables a bandgap, namely a phononic crystal, to be created in the waveguide that can be used to dynamically tune the acoustic transparency in the medium. Our approach will allow the dispersion relation to be locally modified, thus modulating the temporal response of traveling acoustic phonon waves. This novel phonon architecture is promising in terms of realizing the advanced control of phonon dynamics such as waveform and dissipation engineering in the device.

cond-mat.mes-hall↗

arXiv2018

An opto-electro-mechanical system based on evanescently-coupled optical microbottle and electromechanical resonator

Evanescent coupling between a silica optical microbottle resonator and a GaAs electromechanical resonator is demonstrated. This coupling provides high optical sensitivity and efficient piezoelectric controllability of mechanical motion. Opto-electro-mechanical feedback control based on optomechanical detection and electromechanical control is performed in both heating and cooling regimes at room temperature. This feedback scheme can be extended to the efficient control of thermal mechanical motion in electromechanical resonators with arbitrary structures and materials.

cond-mat.mes-hall↗

arXiv2017

Electron Paramagnetic Resonance Spectroscopy of Er$^{3+}$:Y$_2$SiO$_5$ Using Josephson Bifurcation Amplifier: Observation of Hyperfine and Quadrupole Structures

We performed magnetic field and frequency tunable electron paramagnetic resonance spectroscopy of an Er$^{3+}$ doped Y$_2$SiO$_5$ crystal by observing the change in flux induced on a direct current-superconducting quantum interference device (dc-SQUID) loop of a tunable Josephson bifurcation amplifer. The observed spectra show multiple transitions which agree well with the simulated energy levels, taking into account the hyperfine and quadrupole interactions of $^{167}$Er. The sensing volume is about 0.15 pl, and our inferred measurement sensitivity (limited by external flux noise) is approximately $1.5\times10^4$ electron spins for a 1 s measurement. The sensitivity value is two orders of magnitude better than similar schemes using dc-SQUID switching readout.

cond-mat.supr-con↗

arXiv2017

Coherent coupling of dark and bright excitons with vibrational strain

In many physical systems, there are specific electronic states called dark state that are protected from the rapid radiative decay imposed by the system symmetry. Although their long-lived nature indicates their potential for quantum information and spintronic applications, their high stability comes at the expense of optical accessibility. Breaking the symmetry by using magnetic and electric fields has been employed to hybridize dark and bright states thus making them optically active, but high-frequency and on-chip operation remains to be developed. Here we demonstrate the strain-induced coherent coupling of dark and bright exciton states in a GaAs mechanical resonator. The in-plane uniaxial strain breaks the rotational symmetry of the crystal, allowing the dark states to be optically accessible without any external fields. Such dark-bright coupling is tailored by the local strain distribution, which enables the coherent spin operation in the gigahertz regime and opens the way to on-chip excitonic quantum memories and circuits.

cond-mat.mes-hall↗

arXiv2017

Electron paramagnetic resonance spectroscopy using a single artificial atom

Electron paramagnetic resonance (EPR) spectroscopy is an important technology in physics, chemistry, materials science, and biology. Sensitive detection with a small sample volume is a key objective in these areas, because it is crucial, for example, for the readout of a highly packed spin based quantum memory or the detection of unlabeled metalloproteins in a single cell. In conventional EPR spectrometers, the energy transfer from the spins to the cavity at a Purcell enhanced rate plays an essential role and requires the spins to be resonant with the cavity, however the size of the cavity (limited by the wavelength) makes it difficult to improve the spatial resolution. Here, we demonstrate a novel EPR spectrometer using a single artificial atom as a sensitive detector of spin magnetization. The artificial atom, a superconducting flux qubit, provides advantages both in terms of its quantum properties and its much stronger coupling with magnetic fields. We have achieved a sensitivity of $\sim$400 spins/$\sqrt{\mathrm{Hz}}$ with a magnetic sensing volume around $10^{-14} λ^3$ (50 femto-liters). This corresponds to an improvement of two-order of magnitude in the magnetic sensing volume compared with the best cavity based spectrometers while maintaining a similar sensitivity as those spectrometers . Our artificial atom is suitable for scaling down and thus paves the way for measuring single spins on the nanometer scale.

quant-ph↗

arXiv2017

On-chip phononic time lens

The ability to manipulate phonon waveforms in continuous media has attracted significant research interest and is crucial for practical applications ranging from biological imaging to material characterization. Although several spatial focusing techniques have been developed, these systems require sophisticated artificial structures, which limit their practical applications. This is because the spatial control of acoustic phonon waves is not as straightforward as photonics so there is a strong demand for an alternative approach. Here we demonstrate a phononic time lens in a dispersive one-dimensional phononic crystal waveguide, which enables the temporal control of phonon wave propagation. Pulse focusing is realized at a desired time and position with chirped input pulses that agree perfectly with the theoretical prediction. This technique can be applied to arbitrary systems and will offer both an improvement in time and spatial sensing resolution and allow the creation of a highly intense strain field, enabling the investigation of novel nonlinear phononic phenomena such as phononic solitons and rogue waves.

cond-mat.mes-hall↗

arXiv2016

Broadband reconfigurable logic gates in phonon waveguides

The high-quality-factor mechanical resonator in electromechanical systems has facilitated dynamic control of phonons via parametric nonlinear processes and paved the development of mechanical logic-elements. However the resonating element with a narrow bandwidth limits the resultant operation speeds as well as constraining the availability of nonlinear phenomena to a narrow spectral range. To overcome these drawbacks we have developed phonon waveguides in which the mechanical analogue of four-wave-mixing is demonstrated that enables the frequency of phonon waves to be converted over 1 MHz. We harness this platform to execute multiple binary mechanical logic gates in parallel, via frequency division multiplexing in a two-octave-wide phonon transmission band, where each gate can be independently reconfigured. The fidelity of the binary gates is verified via temporal measurements yielding eye diagrams which confirm the availability of high speed logic operations. The phonon waveguide architecture thus offers the broadband functionality that is essential to realising mechanical signal processors.

cond-mat.mes-hall↗

arXiv2016

A strict experimental test of macroscopic realism in a superconducting flux qubit

Macroscopic realism is the name for a class of modifications to quantum theory that allow macroscopic objects to be described in a measurement-independent manner, while largely preserving a fully quantum mechanical description of the microscopic world. Objective collapse theories are examples which aim to solve the quantum measurement problem through modified dynamical laws. Whether such theories describe nature, however, is not known. Here we describe and implement an experimental protocol capable of constraining theories of this class, that is more noise tolerant and conceptually transparent than the original Leggett-Garg test. We implement the protocol in a superconducting flux qubit, and rule out (by ~84 s.d.) those theories which would deny coherent superpositions of 170 nA currents over a ~10 ns timescale. Further, we address the 'clumsiness loophole' by determining classical disturbance with control experiments. Our results constitute strong evidence for the superposition of states of nontrivial macroscopic distinctness.

quant-ph↗

arXiv2016

Observation of collective coupling between an engineered ensemble of macroscopic artificial atoms and a superconducting resonator

The hybridization of distinct quantum systems is now seen as an effective way to engineer the properties of an entire system leading to applications in quantum metamaterials, quantum simulation, and quantum metrology. One well known example is superconducting circuits coupled to ensembles of microscopic natural atoms. In such cases, the properties of the individual atom are intrinsic, and so are unchangeable. However, current technology allows us to fabricate large ensembles of macroscopic artificial atoms such as superconducting flux qubits, where we can really tailor and control the properties of individual qubits. Here, we demonstrate coherent coupling between a microwave resonator and several thousand superconducting flux qubits, where we observe a large dispersive frequency shift in the spectrum of 250 MHz induced by collective behavior. These results represent the largest number of coupled superconducting qubits realized so far. Our approach shows that it is now possible to engineer the properties of the ensemble, opening up the way for the controlled exploration of the quantum many-body system.

quant-ph↗

arXiv2016

A strongly-coupled $Λ$-type micromechanical system

We study a classical $Λ$-type three-level system based on three high-$Q$ micromechanical beam resonators embedded in a gradient electric field. By modulating the strength of the field at the difference frequency between adjacent beam modes, we realize strong dynamic two-mode coupling, via the dielectric force. Driving adjacent pairs simultaneously, we observe the formation of a purely mechanical 'dark' state and an all-phononic analog of coherent population trapping --- signatures of strong three-mode coupling. The $Λ$-type micromechanical system is a natural extention of previously demonstrated 'two-level' micromechanical systems and offers new perspectives on the architecture of all-phononic micromechanical circuits and arrays.

cond-mat.mes-hall↗

arXiv2015

Electron paramagnetic resonance spectroscopy using a dc-SQUID magnetometer directly coupled to an electron spin ensemble

We demonstrate electron spin polarization detection and electron paramagnetic resonance (EPR) spectroscopy using a direct current superconducting quantum interference device (dc-SQUID) magnetometer. Our target electron spin ensemble is directly glued on the dc-SQUID magnetometer that detects electron spin polarization induced by a external magnetic field or EPR in micrometer-sized area. The minimum distinguishable number of polarized spins and sensing volume of the electron spin polarization detection and the EPR spectroscopy are estimated to be $\sim$$10^6$ and $\sim$$10^{-10}$ $\mathrm{cm}^{3}$ ($\sim$0.1 pl), respectively.

cond-mat.mes-hall↗

arXiv2015

Optically detected magnetic resonance of high-density ensemble of NV centers in diamond

Optically detected magnetic resonance (ODMR) is a way to characterize the NV centers. Recently, a remarkably sharp dip was observed in the ODMR with a high-density ensemble of NV centers, and this was reproduced by a theoretical model in [Zhu et al., Nature Communications 5, 3424 (2014)], showing that the dip is a consequence of the spin-1 properties of the NV centers. Here, we present much more details of analysis to show how this model can be applied to investigate the properties of the NV centers. By using our model, we have reproduced the ODMR with and without applied magnetic fields. Also, we theoretically investigate how the ODMR is affected by the typical parameters of the ensemble NV centers such as strain distributions, inhomogeneous magnetic fields, and homogeneous broadening width. Our model could provide a way to estimate these parameters from the ODMR, which would be crucial to realize diamond-based quantum information processing.

quant-ph↗

arXiv2015

Improving the lifetime of the NV center ensemble coupled with a superconducting flux qubit by applying magnetic fields

One of the promising systems to realize quantum computation is a hybrid system where a superconducting flux qubit plays a role of a quantum processor and the NV center ensemble is used as a quantum memory. We have theoretically and experimentally studied the effect of magnetic fields on this hybrid system, and found that the lifetime of the vacuum Rabi oscillation is improved by applying a few mT magnetic field to the NV center ensemble. Here, we construct a theoretical model to reproduce the vacuum Rabi oscillations with/without magnetic fields applied to the NV centers, and we determine the reason why magnetic fields can affect the coherent properties of the NV center ensemble. From our theoretical analysis, we quantitatively show that the magnetic fields actually suppress the inhomogeneous broadening from the strain in the NV centers.

quant-ph↗

arXiv2015

Phonon propagation dynamics in band-engineered one-dimensional phononic crystal waveguides

The phonon propagation dynamics in a phononic crystal waveguide, realized via a suspended one-dimensional membrane array with periodic air holes, is investigated as function of its geometry. The bandstructure of the phononic crystal can be engineered by modifying the characteristics of the phonon standing waves in the waveguide by varying the waveguide width and the pitch of the air holes. This enables the phonon transmission bands, the bandgaps, the velocity and the nonlinear dispersion in the phononic crystal to be controlled. Indeed the engineered bandstructure can also be tuned to sustain multiple phonon modes in a given branch which whilst being spectrally degenerate can be temporally resolved via their differing group velocities. This systematic study reveals the key geometric parameters that enable the phonon transport in phononic crystal waveguides to be fully controlled.

cond-mat.mes-hall↗

arXiv2015

Ising interaction between capacitively-coupled superconducting flux qubits

Here, we propose a scheme to generate a controllable Ising interaction between superconducting flux qubits. Existing schemes rely on inducting couplings to realize Ising interactions between flux qubits, and the interaction strength is controlled by an applied magnetic field On the other hand, we have found a way to generate an interaction between the flux qubits via capacitive couplings. This has an advantage in individual addressability, because we can control the interaction strength by changing an applied voltage that can be easily localized. This is a crucial step toward the realizing superconducting flux qubit quantum computation.

quant-ph↗

arXiv2014

Robust entanglement-based magnetic field sensor beyond the standard quantum limit

Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.

quant-ph↗

arXiv2014

Improving the coherence time of a quantum system via a coupling with an unstable system

Here, we propose a counter-intuitive use of a hybrid system where the coherence time of a quantum system is actually improved via a coupling with an unstable system. If we couple a two-level system with a single NV center, then a dark state of the NV center naturally forms after the hybridization. We show that this dark state becomes robust against environmental fluctuations due to the coupling even when the coherence time of the two-level system is much shorter than that of the NV center. Our proposal opens a new way to use a quantum hybrid system for the realization of robust quantum information processing

quant-ph↗