Optomechanical Coupling Rate Research Articles

Coupling ideality of standing-wave supermode microresonators

Standing-wave supermode microresonators that are created through the strong coupling between counter-propagating modes have emerged as versatile platforms for sensing and nonlinear optics. For example, these microresonators have shown potential in nanoparticle sizing and counting, as well as enhancing the single-photon optomechanical coupling rate of stimulated Brillouin scattering. However, it has been observed that the relation between the mode linewidth and on-resonance transmission of the split supermodes differs obviously from that of the non-split modes. This behavior is typically quantified by the coupling ideality (I), which remains inadequately explored for the standing-wave supermodes. In this study, we theoretically and experimentally investigate the coupling ideality of standing-wave supermodes in a commonly employed configuration involving a SiO2 microresonator side-coupled to a tapered fiber. Our findings demonstrate that, even with a single-mode tapered fiber, the coupling ideality of the standing-wave supermodes is limited to 0.5, due to the strong backscattering-induced energy loss into the counter-propagating direction, resulting in an additional equivalent parasitic loss. While achieving a coupling ideality of 0.5 presents challenges for reaching over-coupled regimes, it offers a convenient approach for adjusting the total linewidth of the modes while maintaining critically-coupled conditions.

Optomechanical Coupling Optimization in Engineered Nanocavities

AbstractIn optomechanics, the interaction between light and matter is enhanced by engineering cavities where the electromagnetic field and the mechanical displacement are confined simultaneously within the same volume. This leads to a wide range of interesting phenomena, such as optomechanically induced transparency and the cooling of macroscopic objects to their lowest possible motion state. In this manuscript, the focus is on designed optomechanical cavities exploiting heterostructures in air‐slot photonic‐crystal waveguides, incorporating different hole shapes and dimensions to engineer and control their optomechanical properties. The aim is to maximize the optical quality factor of the optical cavity, while ensuring optical mode volumes below the diffraction limit. These optimized optical modes interact with in‐plane motional degrees of freedom of the structures achieving high optomechanical coupling rates, thus opening up the possibility of mechanical amplification, nonlinear dynamics and chaos through the optomechanical back‐action.

Influence of thermal effects on the optomechanical coupling rate in acousto-optic cavities

Influence of thermal effects on the optomechanical coupling rate in acousto-optic cavities

Multimode optomechanics with a two-dimensional optomechanical crystal

Chip-scale multimode optomechanical systems have unique benefits for sensing, metrology, and quantum technologies relative to their single-mode counterparts. Slot-mode optomechanical crystals enable sideband resolution and large optomechanical couplings of a single optical cavity to two microwave-frequency mechanical modes. Still, previous implementations have been limited to nanobeam geometries, whose effective quantum cooperativity at ultralow temperatures is limited by their low thermal conductance. In this work, we design and experimentally demonstrate a two-dimensional mechanical–optical–mechanical (MOM) platform that dispersively couples a slow-light slot-guided photonic-crystal waveguide mode and two slow-sound ∼ 7 GHz phononic wire modes localized in physically distinct regions. We first demonstrate optomechanical interactions in long waveguide sections, unveiling acoustic group velocities below 800 m/s, and then move on to mode-gap adiabatic heterostructure cavities with a tailored mechanical frequency difference. Through optomechanical spectroscopy, we demonstrate optical quality factors Q ∼ 105, vacuum optomechanical coupling rates, go/2π, of 1.5 MHz, and dynamical back-action effects beyond the single-mode picture. At a larger power and adequate laser-cavity detuning, we demonstrate regenerative optomechanical oscillations involving a single mechanical mode, extending to both mechanical modes through modulation of the input laser drive at their frequency difference. This work constitutes an important advance toward engineering MOM systems with nearly degenerate mechanical modes as part of hybrid multipartite quantum systems.

Dissipative optomechanics in high-frequency nanomechanical resonators

The coherent transduction of information between microwave and optical domains is a fundamental building block for future quantum networks. A promising way to bridge these widely different frequencies is using high-frequency nanomechanical resonators interacting with low-loss optical modes. State-of-the-art optomechanical devices rely on purely dispersive interactions that are enhanced by a large photon population in the cavity. Additionally, one could use dissipative optomechanics, where photons can be scattered directly from a waveguide into a resonator hence increasing the degree of control of the acousto-optic interplay. Hitherto, such dissipative optomechanical interaction was only demonstrated at low mechanical frequencies, precluding prominent applications such as the quantum state transfer between photonic and phononic domains. Here, we show the first dissipative optomechanical system operating in the sideband-resolved regime, where the mechanical frequency is larger than the optical linewidth. Exploring this unprecedented regime, we demonstrate the impact of dissipative optomechanical coupling in reshaping both mechanical and optical spectra. Our figures represent a two-order-of-magnitude leap in the mechanical frequency and a tenfold increase in the dissipative optomechanical coupling rate compared to previous works. Further advances could enable the individual addressing of mechanical modes and help mitigate optical nonlinearities and absorption in optomechanical devices.

Heterogeneous optomechanical crystal cavity coupled by a wavelength-scale mechanical waveguide

Integrated optomechanical crystal (OMC) cavities provide a vital device prototype for highly efficient microwave to optical conversion in quantum information processing. In this work, we propose a novel heterogeneous OMC cavity consisting of a thin-film lithium niobate (TFLN) slab and chalcogenide (ChG) photonic crystal nanobeam coupled by a wavelength-scale mechanical waveguide. The optomechanical coupling rate of the heterogeneous OMC cavity is optimized up to 340 kHz at 1.1197 GHz. Combined with phononic band and power decomposition, 17.38% energy from the loaded RF power is converted into dominant fundamental horizontal shear mode (SH0) in the narrow LN mechanical waveguide. Based on this fraction, as a result, 3.51% power relative to the loaded RF energy is scattered into the fundamental longitudinal mode (L0) facing the TFLN-ChG heterogeneous waveguide. The acoustic breathing mode of the heterogeneous OMC is successfully excited under the driving of the propagating L0 mode in the heterogeneous waveguide, demonstrating the great potentials of the heterogeneous piezo-optomechanical transducer in high-performance photon–phonon interaction fields.

Levitated Optomechanics with Meta-Atoms.

We propose to introduce additional control in levitated optomechanics by trapping a meta-atom, i.e., a subwavelength and high-permittivity dielectric particle supporting Mie resonances. In particular, we theoretically demonstrate that optical levitation and center-of-mass ground-state cooling of silicon nanoparticles in vacuum is not only experimentally feasible but it offers enhanced performance over widely used silica particles in terms of trap frequency, trap depth, and optomechanical coupling rates. Moreover, we show that, by adjusting the detuning of the trapping laser with respect to the particle's resonance, the sign of the polarizability becomes negative, enabling levitation in the minimum of laser intensity, e.g., at the nodes of a standing wave. The latter opens the door to trapping nanoparticles in the optical near-field combining red and blue-detuned frequencies, in analogy to two-level atoms, which is of interest for generating strong coupling to photonic nanostructures and short-distance force sensing.

Parameter investigations on lithium-niobate-based photonic crystal optomechanical cavity

In this paper, to fully understand the influence of nanofabrication error issues on the lithium-niobate-based device, the systematic simulations and optimizations of lithium-niobate-based photonic crystal (PhC) optomechanical cavity considering the material dispersion and inclination angle of PhC air hole are investigated in details. The structural parameter influences on the PhC band gap, the line defected waveguide transmission characteristics, the optical resonant wavelength of the PhC microcavity, and the mechanical resonant frequency are all discussed. The effects of the simulation methods on the PhC band gap are investigated as well. And finally, the opto-mechanical coupling rate of the lithium-niobate-based PhC optomechanical cavity structure is calculated. Such obtained results can help researchers to precisely design the required optomechanical cavity for specific applications.

Study on the Acousto-Optic Coupling Effect of a One-Dimensional Hetero-Optomechanical Crystal Nanobeam Resonator

The optomechanical crystal nanobeam resonator has attracted the attention of researchers due to its high optomechanical coupling rate and small modal volume. In this study, we propose a high-optomechanical-coupling-rate heterostructure with a gradient cavity, and the optomechanical rates of the single mirror and hetero-optomechanical crystal nanobeam resonators are calculated. The results demonstrate that the heterostructure based on the utilization of two mirror regions realizes better confinement of the optical and mechanical modes. In addition, the mechanical breathing mode at 9.75 GHz and optical mode with a working wavelength of 1.17 μm are demonstrated with an optomechanical coupling rate g0 = 3.81 MHz between them, and the mechanical quality factor is increased to 3.18 × 106.

Engineering Multiple GHz Mechanical Modes in Optomechanical Crystal Cavities

Optomechanical crystal cavities (OMCCs) are fundamental nanostructures for a wide range of phenomena and applications. Usually, optomechanical interaction in such OMCCs is limited to a single optical mode and a unique mechanical mode. In this sense, eliminating the single-mode constraint---for instance, by adding more mechanical modes---should enable more complex physical phenomena, giving rise to a context of multimode optomechanical interaction. However, a general method to produce in a controlled way multiple mechanical modes with large coupling rates in OMCCs is still missing. In this work, we present a route to confine multiple GHz mechanical modes coupled to the same optical field with similar optomechanical coupling rates---up to 400 kHz---by OMCC engineering. In essence, we increase the number of unit cells (consisting of a silicon nanobrick perforated by circular holes with corrugations at both its sides) in the adiabatic transition between the cavity center and the mirror region. Remarkably, the mechanical modes in our cavities are located within a full phononic band gap, which is a key requirement to achieve ultrahigh mechanical $Q$ factors at cryogenic temperatures. The multimode behavior in a full phononic band gap and the easiness of realization using standard silicon nanotechnology make our OMCCs highly appealing for applications in the classical and quantum realms.

Large Single-Phonon Optomechanical Coupling Between Quantum Dots and Tightly Confined Surface Acoustic Waves in the Quantum Regime

Surface acoustic waves (SAWs) coupled to quantum dots (QDs), trapped atoms and ions, and point defects have been proposed as quantum transduction platforms, yet the requisite coupling rates and cavity lifetimes have not been experimentally established. Although the interaction mechanism varies, small acoustic cavities with large zero-point motion are required for high efficiencies. We experimentally establish the feasibility of this platform through electro- and optomechanical characterization of tightly focusing, single-mode Gaussian SAW cavities at approximately 3.6 GHz on $\mathrm{Ga}\mathrm{As}$. We explore the performance limits of the platform by fabricating SAW cavities with mode volumes approaching $6{\ensuremath{\lambda}}^{3}$ and linewidths less than 1 MHz. Employing strain-coupled single $\mathrm{In}\mathrm{As}$ QDs as optomechanical intermediaries, we measure single-phonon optomechanical coupling rates ${g}_{0}\ensuremath{\approx}2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}1.2$ MHz. Sideband scattering rates thus exceed intrinsic phonon loss, indicating the potential for quantum optical readout and transduction of cavity phonon states. To demonstrate the feasibility of this platform for low-noise ground-state quantum transduction, we develop a fiber-based confocal microscope in a dilution refrigerator and perform single-QD resonance fluorescence sideband spectroscopy at millikelvin temperatures. These measurements show conversion between microwave phonons and optical photons with sub-natural linewidths.

Laser Cooling of a Lattice Vibration in van der Waals Semiconductor.

Laser cooling atoms and molecules to ultralow temperatures has produced plenty of opportunities in fundamental physics, precision metrology, and quantum science. Although theoretically proposed over 40 years, the laser cooling of certain lattice vibrations (i.e., phonon) remains a challenge owing to the complexity of solid structures. Here, we demonstrate Raman cooling of a longitudinal optical phonon in two-dimensional semiconductor WS2 by red-detuning excitation at the sideband of the exciton (bound electron-hole pair). Strong coupling between the phonon and exciton and appreciable optomechanical coupling rates provide access to cooling high-frequency phonons that are robust against thermal decoherence even at room temperature. Our experiment opens possibilities of laser cooling and control of individual optical phonon and, eventually, possible cooling of matter in van der Waals semiconductor.

Microwave-to-optical conversion with a gallium phosphide photonic crystal cavity

Electrically actuated optomechanical resonators provide a route to quantum-coherent, bidirectional conversion of microwave and optical photons. Such devices could enable optical interconnection of quantum computers based on qubits operating at microwave frequencies. Here we present a platform for microwave-to-optical conversion comprising a photonic crystal cavity made of single-crystal, piezoelectric gallium phosphide integrated on pre-fabricated niobium circuits on an intrinsic silicon substrate. The devices exploit spatially extended, sideband-resolved mechanical breathing modes at ~3.2 GHz, with vacuum optomechanical coupling rates of up to g0/2π ≈ 300 kHz. The mechanical modes are driven by integrated microwave electrodes via the inverse piezoelectric effect. We estimate that the system could achieve an electromechanical coupling rate to a superconducting transmon qubit of ~200 kHz. Our work represents a decisive step towards integration of piezoelectro-optomechanical interfaces with superconducting quantum processors.

Hetero-Optomechanical Crystal Zipper Cavity for Multimode Optomechanics

Multimode optomechanics exhibiting several intriguing phenomena, such as coherent wavelength conversion, optomechanical synchronization, and mechanical entanglements, has garnered considerable research interest for realizing a new generation of information processing devices and exploring macroscopic quantum effect. In this study, we proposed and designed a hetero-optomechanical crystal (OMC) zipper cavity comprising double OMC nanobeams as a versatile platform for multimode optomechanics. Herein, the heterostructure and breathing modes with high mechanical frequency ensured the operation of the zipper cavity at the deep-sideband-resolved regime and the mechanical coherence. Consequently, the mechanical breathing mode at 5.741 GHz and optical odd mode with an intrinsic optical Q factor of 3.93 × 105 were experimentally demonstrated with an optomechanical coupling rate g0 = 0.73 MHz between them, which is comparable to state-of-the-art properties of the reported OMC. In addition, the hetero-zipper cavity structure exhibited adequate degrees of freedom for designing multiple mechanical and optical modes. Thus, the proposed cavity will provide a playground for studying multimode optomechanics in both the classical and quantum regimes.

Optical Control of Bulk Phonon Modes in Crystalline Solids

AbstractLong‐lived phonons within crystalline bulk acoustic wave (BAW) resonators have become coherent carriers of information, which can be utilized for a variety of scientific and technological applications. Herein, a brief introduction to the field of phonon control is given with an emphasis on bulk phonons at high frequencies within crystalline solids. In cavity optomechanics, the photons and phonons can be confined by material boundaries, yielding large optomechanical coupling rates at gigahertz (GHz) frequencies, but the spurious heating is detrimental to robust operation. Although electromechanical techniques can be used to access long‐lived phonons in piezoelectric crystals, they are not suitable for the study of non‐piezoelectric crystals. The phase‐matched Brillouin interactions enable efficient optical access GHz frequency mechanical modes within macroscopic crystalline solids. Combining with the well‐established framework of cavity optomechanics, efficient optical control of BAWs can be obtained. For optical phonons, strong spontaneous Raman cooling and heating based on the interaction between excitons and phonons are considered. In addition, the application of optical phonons in quantum memory at room temperature is introduced. The review finishes with a discussion of the research direction for bulk optomechanical systems and exciton–phonon coupling systems in the future.

Acousto-optic cavity coupling in 2D phoxonic crystal with combined convex and concave holes

A two-dimensional cross-like phoxonic crystal (PxC) model is proposed, which exhibits simultaneously large complete photonic crystal (PtC) and phononic crystal (PnC) bandgaps. The most salient trait of the structure is the wide range of geometrical parameters compatible with large complete bandgaps. After geometrical optimization, photonic and phononic bandgaps with gap-to-midgap ratios of 11.5% and 90.7% are obtained, respectively. These values are close to the best topology-optimized reported values but are obtained with simple shapes compatible with nanoscale fabrication technology. These characteristics make the convex–concave topology a promising candidate for PxC devices. A cavity is then introduced by filling up one cross-like hole in the 7 × 7 super-cell. PtC and PnC bands with defects appear in the respective large complete bandgaps, confining phonons and photons in the same cavity. Acousto-optic (AO) coupling between photonic and phononic defect modes is further investigated by the finite element method, taking both photoelastic and moving interface mechanisms into consideration. The symmetries of both photonic and phononic modes play a dominant role in the coupling strength. Results show that the strongest linear coupling between a photonic transverse magnetic mode and phononic breathing mode is obtained due to the in-phase superposition in the x and y directions. A quadratic nonlinear coupling is observed when photonic modes are coupled with the phononic stretching mode due to the inverse superposition of x and y directions. Finally, the optomechanical coupling rates relative to zero-point motion are estimated.

Strong optomechanical coupling in chain-like waveguides of silicon nanoparticles with quasi-bound states in the continuum

We propose and demonstrate that strong optomechanical coupling can be achieved in a chain-like waveguide consisting of silicon nanorods. By employing quasi-bound states in the continuum and mechanical resonances at a frequency around 10 GHz, the optomechanical coupling rate can be above 2 MHz and surpass most microcavities. We have also studied cases with different optical wave numbers and size parameters of silicon, and a robust coupling rate has been verified, benefiting the experimental measurements and practical applications. The proposed silicon chain-like waveguide of strong optomechanical coupling may pave new ways for research on photon-phonon interaction with microstructures.

Phonon lasing in a hetero optomechanical crystal cavity

Micro- and nanomechanical resonators have emerged as promising platforms for sensing a broad range of physical properties, such as mass, force, torque, magnetic field, and acceleration. The sensing performance relies critically on the motional mass, mechanical frequency, and linewidth of the mechanical resonator. Herein, we demonstrate a hetero optomechanical crystal (OMC) cavity based on a silicon nanobeam structure. The cavity supports phonon lasing in a fundamental mechanical mode with a frequency of 5.91 GHz, an effective mass of 116 fg, and a mechanical linewidth narrowing in the range from 3.3 MHz to 5.2 kHz, while the optomechanical coupling rate is as high as 1.9 MHz. With this phonon laser, on-chip sensing can be predicted with a resolution of δ λ / λ = 1.0 × 10 − 8 . The use of a silicon-based hetero OMC cavity that harnesses phonon lasing could pave the way toward high-precision sensors that allow silicon monolithic integration and offer unprecedented sensitivity for a broad range of physical sensing applications.

Nonsuspended optomechanical crystal cavities using As2S3 chalcogenide glass

An optomechanical crystal cavity with nonsuspended structure using As 2 S 3 material is proposed. The principle of mode confinement in the nonsuspended cavity is analyzed, and two different types of optical and acoustic defect modes are calculated through appropriate design of the cavity structure. An optomechanical coupling rate of 82.3 kHz is obtained in the proposed cavity, and the designed acoustic frequency is 3.44 GHz. The acoustic mode coupling between two nonsuspended optomechanical crystal cavities is also demonstrated, showing that the proposed cavity structure has great potential for realizing further optomechanical applications in multicavity systems.

Absolute Determination of the Single-Photon Optomechanical Coupling Rate via a Hopf Bifurcation

We establish a method for the determination of the single-photon optomechanical coupling rate, which characterizes the radiation pressure interaction in an optomechanical system. The estimation of the rate with which a mechanical oscillator, initially in a thermal state, undergoes a Hopf bifurcation, and reaches a limit cycle, allows us to determine the single-photon optomechanical coupling rate in a simple and consistent way. Most importantly, and in contrast to other methods, our method does not rely on knowledge of the system's bath temperature and on a calibration of the signal. We provide the theoretical framework, and experimentally validate this method, providing a procedure for the full characterization of an optomechanical system, which could be extended outside cavity optomechanics, whenever a resonator is driven into a limit cycle by the appropriate interaction with another degree of freedom.