Optomechanical Crystals Research Articles

High Q-Factor Diamond Optomechanical Resonators with Silicon Vacancy Centers at Millikelvin Temperatures.

Phonons are envisioned as coherent intermediaries between different types of quantum systems. Engineered nanoscale devices, such as optomechanical crystals (OMCs), provide a platform to utilize phonons as quantum information carriers. Here we demonstrate OMCs in diamond designed for strong for interactions between phonons and a silicon vacancy (SiV) spin. Using optical measurements at millikelvin temperatures, we measure a line width of 13 kHz (Q-factor of ∼4.4 × 105) for a 6 GHz acoustic mode, a record for diamond in the GHz frequency range and within an order of magnitude of state-of-the-art line widths for OMCs in silicon. We investigate SiV optical and spin properties in these devices and outline a path toward a coherent spin-phonon interface.

In situ tuning of optomechanical crystals with nano-oxidation

Optomechanical crystals are a promising device platform for quantum transduction and sensing. Precise targeting of the optical and acoustic resonance frequencies of these devices is crucial for future advances on these fronts. However, fabrication disorder in these wavelength-scale nanoscale devices typically leads to inhomogeneous resonance frequencies. Here we achieve in situ, selective frequency tuning of optical and acoustic resonances in silicon optomechanical crystals via electric field-induced nano-oxidation using an atomic-force microscope. Our method can achieve a tuning range >2nm (0.13%) for the optical resonance wavelength in the telecom C-band, and >60MHz (1.2%) for the acoustic resonance frequency at 5 GHz. The tuning resolution of 1.1 pm for the optical wavelength and 150 kHz for the acoustic frequency allows us to spectrally align multiple optomechanical crystal resonators using a pattern generation algorithm. Our results establish a method for precise post-fabrication tuning of optomechanical crystals. This technique can enable coupled optomechanical resonator arrays, scalable resonant optomechanical circuits, and frequency matching of microwave-optical quantum transducers.

Experimental Evaluation of All-Optical Up- and Down-Conversion of 3GPP 5G NR Signals using an Optomechanical Crystal Cavity Frequency Comb

Experimental Evaluation of All-Optical Up- and Down-Conversion of 3GPP 5G NR Signals using an Optomechanical Crystal Cavity Frequency Comb

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.

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.

Clamped and sideband-resolved silicon optomechanical crystals

Optomechanical crystals (OMCs) are a promising and versatile platform for transduction between mechanical and optical fields. However, the release from the substrate used in conventional suspended OMCs also complicates manufacturing and severely reduces thermal anchoring. This may be improved by attaching the OMCs directly to the substrate. Previous work towards such clamped, i.e., non-suspended, OMCs suffers from weak interaction rates and insufficient lifetimes. Here, we present a class of clamped OMCs realizing—for the first time, to our knowledge—optomechanical interactions in the resolved-sideband regime required for quantum transduction. Our approach leverages high-wavevector mechanical modes outside the continuum. We observe a record zero-point optomechanical coupling rate of g0/(2π)≈0.50MHz along with a sevenfold improvement in the single-photon cooperativity of clamped OMCs. Our devices operate at frequencies commonly used in superconducting qubits. This opens an avenue using clamped OMCs in both classical and quantum communications, sensing, and computation through scalable mechanical circuitry that couples strongly to light.

Optical bistability and four-wave mixing response of a quantum dot coupled to an optomechanical photonic crystal nanocavity

We theoretically explore the nonlinear optical response including optical bistability and four-wave mixing (FWM) process in a hybrid cavity quantum electrodynamic (C-QED) system. The hybrid C-QED system consists of a quantum dot (QD) which is coherently driven by two-tone laser fields and embedded in an optomechanical photonic crystal (PhC) nanocavity. Our theoretical analysis demonstrates optical bistability, where the steady-state photon number follows a constant rise in the gain of the switch by controlling a strong pump field driving the QD. A strong coupling between quantised fields and matter (e.g. in optical cavities) is a successful approach for conventionally modifying the dressed state and by altering the field parameters, the modulation of QD dressed state is accomplished. In addition, we list the influence of off-resonant detuning, exciton-nanocavity coupling strength and Rabi coupling strength in our proposed system which generates a controllable four-wave mixing (FWM) signal in the output probe field of the system. The intensity of the FWM is significantly changed when strong coupling and high pump power are present simultaneously and results in the formation of an optomechanically induced transparency (OMIT) window and slow light. The investigation of the proposed system have potential application towards on-chip QD-based nanophotonic devices.

Phoxonic bandgap modulation in optomechanical crystals with shifting hole

Optomechanical crystals (OMCs) control light and mechanical vibrations by simultaneously presenting photonic and phononic bandgaps. Tuning the position of these bandgaps is essential to address different technological applications. In this study, we present a one-dimensional OMC with wings and a hole whose position is shifting sideways. Simulations of the photonic and phononic band diagrams show that the hole shift effectively controls the width and position of the band gaps. Furthermore, the hole shift also opens new photonic bandgaps that extend the frequency range with full photonic bandgaps. The width of the phononic bandgap is maximum for a hole shift to be 42% wider than without a hole shift. Despite large band movements induced by the hole shift, the average displacement is null, which means that the hole shift does not impact the photon and phonon density of states (DOS). These results can be used to optimize the design of optomechanical cavities for specific frequency range applications.

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.

Synchronization of Optomechanical Oscillators in Coupled 1D Optomechanical Crystal Nanobeam Cavities

We proposed a new optomechanical system (OMS) based on parallel suspended one-dimensional optomechanical crystal (1D-OMC) nanobeam cavities for optomechanical synchronization. The optomechanical oscillators (OMOs) were spaced apart by an air-slot gap and coupled through optical radiation fields. The numerical simulation showed that the evolution process of 1D-OMC nanobeam cavities to mechanical synchronization could be divided into three clear stages. The synchronization of two mechanical breathing modes at 5.8846 GHz was achieved by using a single laser source. Finally, we investigated the relationship between the threshold power and detuning of an input laser for self-sustaining and synchronization states. Such chip-based structures hold great potential for large-scale synchronized oscillator networks.

Homodyne coherent quantum noise cancellation in a hybrid optomechanical force sensor

In this paper we propose an experimentally viable scheme to enhance the sensitivity of force detection in a hybrid optomechanical setup assisted by squeezed vacuum injection, beyond the standard quantum limit (SQL). The scheme is based on a combination of the coherent quantum noise cancellation (CQNC) strategy with a variational homodyne detection of the cavity output spectrum in which the phase of the local oscillator is optimized. In CQNC, realizing a negative-mass oscillator in the system leads to exact cancellation of the backaction noise from the mechanics due to destructive quantum interference. Squeezed vacuum injection enhances this cancellation and allows sub-SQL sensitivity to be reached in a wide frequency band and at much lower input laser powers. We show here that the adoption of variational homodyne readout enables us to enhance this noise cancellation up to $40\phantom{\rule{3.33333pt}{0ex}}\mathrm{dB}$ compared to the standard case of detection of the optical output phase quadrature, leading to a remarkable force sensitivity of the order of ${10}^{\ensuremath{-}19}\phantom{\rule{0.28em}{0ex}}\mathrm{N}/\sqrt{\mathrm{Hz}}$, about $70%$ enhancement compared to the standard case. Moreover, we show that at nonzero cavity detuning, the signal response can be amplified at a level three to five times larger than that in the standard case without variational homodyne readout, improving the signal-to-noise ratio. Finally, the variational readout CQNC developed in this paper may be applied to other optomechanical-like platforms such as levitated systems and multimode optomechanical arrays or crystals as well as Josephson-based optomechanical systems.

Optomechanical crystal with bound states in the continuum

Chipscale micro- and nano-optomechanical systems, hinging on the intangible radiation-pressure force, have shown their unique strength in sensing, signal transduction, and exploration of quantum physics with mechanical resonators. Optomechanical crystals, as one of the leading device platforms, enable simultaneous molding of the band structure of optical photons and microwave phonons with strong optomechanical coupling. Here, we demonstrate a new breed of optomechanical crystals in two-dimensional slab-on-substrate structures empowered by mechanical bound states in the continuum (BICs) at 8 GHz. We show symmetry-induced BIC emergence with optomechanical couplings up to g/2π ≈ 2.5 MHz per unit cell, on par with low-dimensional optomechanical crystals. Our work paves the way towards exploration of photon-phonon interaction beyond suspended microcavities, which might lead to new applications of optomechanics from phonon sensing to quantum transduction.

Chiral spin-phonon bound states and spin-spin interactions with phononic lattices

Designing unconventional interactions between single phonons and spins is fascinating for its applications in quantum phononics. Here we propose a reliable scheme for coupling spins and phonons in phononic dimer and trimer lattices, with the combination of solid-state defects and diamond phononic (optomechanical) crystals. The dimer and trimer lattices used are an array of coupled phononic cavities with spatially modulated hopping rates. We predict a series of unconventional sound-matter interaction phenomena in this hybrid quantum system. In the dimer lattice we show the formation of chiral spin-phonon bound states and topology-dependent phononic collective radiation. While in the trimer lattice, chiral bound states still exist and the spin relaxation is sublattice dependent. The chiral bound states existing in both types of lattices are robust to a large amount of disorder, which can mediate chiral and robust spin-spin interactions. This work provides a promising platform for phonon-based quantum information processing and quantum simulation.

Deep sub-wavelength localization of light and sound in dielectric resonators.

Optomechanical crystals provide coupling between phonons and photons by confining them to commensurate wavelength-scale dimensions. We present a new concept for designing optomechanical crystals capable of achieving unprecedented coupling rates by confining optical and mechanical waves to deep sub-wavelength dimensions. Our design is based on a dielectric bowtie unit cell with an effective optical/mechanical mode volume of 7.6 × 10-3(λ/nSi)3/1.2×10-3 λ mech 3. We present results from numerical modeling, indicating a single-photon optomechanical coupling of 2.2 MHz with experimentally viable parameters. Monte Carlo simulations are used to demonstrate the design's robustness against fabrication disorder.

Reservoir-Engineered Spin Squeezing: Macroscopic Even-Odd Effects and Hybrid-Systems Implementations

We revisit the dissipative approach to producing and stabilizing spin-squeezed states of an ensemble of $N$ two-level systems, providing a detailed analysis of two surprising yet generic features of such protocols. The first is a macroscopic sensitivity of the steady state to whether $N$ is even or odd. We discuss how this effect can be avoided (if the goal is parity-insensitive squeezing), or could be exploited as a new kind of sensing modality to detect the addition or removal of a single spin. The second effect is an anomalous emergent long timescale and a "prethermalized" regime that occurs for even weak single-spin dephasing. This effect allows one to have strong spin squeezing over a long transient time even though the level of spin squeezing in the steady state is very small. We also discuss a general hybrid-systems approach for implementing dissipative spin squeezing that does not require squeezed input light or complex multi-level atoms, but instead makes use of bosonic reservoir-engineering ideas. Our protocol is compatible with a variety of platforms, including trapped ions, NV defect spins coupled to diamond optomechanical crystals, and spin ensembles coupled to superconducting microwave circuits.

Piezoelectric Optomechanical Approaches for Efficient Quantum Microwave‐to‐Optical Signal Transduction: The Need for Co‐Design

AbstractPiezoelectric optomechanical platforms represent one of the most promising routes toward achieving quantum transduction of photons between the microwave and optical frequency domains. However, there are significant challenges to achieving near‐unity transduction efficiency. The authors discuss such factors in the context of the two main approaches being pursued for high efficiency transduction. The first approach uses 1D nanobeam optomechanical crystals excited by interdigitated transducers and is characterized by large single‐photon optomechanical coupling strength, limited intracavity pump photon population to avoid absorption‐induced heating (at cryogenic temperature), and low phonon injection efficiency from the transducer to the optomechanical cavity. The second approach uses (quasi) bulk acoustic wave resonators integrated into photonic Fabry–Perot cavity geometries and is characterized by low single‐photon optomechanical coupling strength, high intracavity pump photon population without significant heating, and high phonon injection efficiency. After reviewing the current status of both approaches, the need for co‐designing the electromechanical and optomechanical sub‐systems is discussed in order to achieve high transduction efficiencies, taking the GaAs piezo‐optomechanical platform as an example.

Unconventional Quantum Sound-Matter Interactions in Spin-Optomechanical-Crystal Hybrid Systems.

We predict a set of unusual quantum acoustic phenomena resulting from sound-matter interactions in a fully tunable solid-state platform in which an array of solid-state spins in diamond are coupled to quantized acoustic waves in a one-dimensional optomechanical crystal. We find that, by using a spatially varying laser drive that introduces a position-dependent phase in the optomechanical interaction, the mechanical band structure can be tuned insitu, consequently leading to unconventional quantum sound-matter interactions. We show that quasichiral sound-matter interactions can occur, with tunable ranges from bidirectional to quasiunidirectional, when the spins are resonant with the bands. When the solid-state spin frequency lies within the acoustic band gap, we demonstrate the emergence of an exotic polariton bound state that can mediate long-range tunable, odd-neighbor, and complex spin-spin interactions. This work expands the present exploration of quantum phononics and can have wide applications in quantum simulations and quantum information processing.

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.

Optomechanical crystals for spatial sensing of submicron sized particles

Optomechanical crystal cavities (OMC) have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of OMCs operating under ambient conditions as a sensor of submicrometer particles by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region. OMCs have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, viruses and bacteria.

Novel one-dimensional optomechanical crystal nanobeam with high optomechanical coupling rate under different defect states

Optomechanical crystals can simultaneously modulate elastic waves and electromagnetic waves as well as localizing phonons and photons to enhance the acousto-optic interaction. In this work, a new type of optomechanical crystal nanobeam cavity is designed by periodically arranging the unit cells with double holes on both sides of a hexagonal prism. Considering the moving boundary effect and the photoelastic effect as well as using the first-order electromagnetic perturbation theory and the optomechanical coupling coefficient calculation method, the optomechanical coupling rate of the structure is calculated. The result shows that the overlap between the optical mode and the mechanical mode can be improved by changing the number of defects and optimizing the geometric structure. For the nanobeam cavity structures with different numbers of the like defects, the number of defects will only affect the action mode of the moving boundary effect and photoelastic effect in the optomechanical coupling rate, but will not change the coupling rate too much. In particular, the optomechanical coupling rate of the single defect optomechanical crystal nanobeam cavity can reach –1.29 MHz, and the equivalent mass is 42.6 fg. Moreover, the designed structure is simple and easy to process and fabricate. The coupling rate of even-symmetric optomechanical crystal nanobeam cavity based on gradient defect can reach 2.25 MHz, and the coupling rate of odd symmetric structure can reach 2.18 MHz, in which the moving boundary effect is dominant. Based on the symmetry analysis of the vibration modes of the optomechanical crystal nanobeam cavity with gradient defects, it is worth noting that only the even symmetrical vibration modes of <i>x</i>-<i>y</i>, <i>x</i>-<i>z</i> and <i>y</i>-<i>z</i> can strongly couple with the optical modes. The surface density of the moving boundary effect is calculated and analyzed, and it is found that the surface density of the acoustic resonance mode with high symmetry also possesses high symmetry. However, when the surface density of the moving boundary effect in the defect state appears adjacent to each other and cancels out each other, it will destroy the coupling mode of the moving boundary effect and reduce the coupling rate, whether the symmetry is high or low. In addition, the designed optomechanical crystal nanobeam can also improve the quality factor of the resonant cavity by optimizing the defect structure while maintaining a high optomechanical coupling rate. Therefore, this research provides an effective means to find a structure with high optomechanical coupling rate, and also presents the ideas for designing the space sensors.