Using inverse-design and a novel design pattern which breaks crystal periodicity, we demonstrate experimentally the, to our knowledge, highest vacuum optomechanical interaction rate for release-free systems at 770 kHz.

Interactions between light and mechanics provide a powerful interface between optical and microwave-frequency signals, with applications spanning classical signal processing and quantum technologies. High-performance optomechanical devices require both strong photon-phonon coupling and tolerance to parasitic laser heating. Release-free optomechanical crystals provide improved thermal anchoring compared to suspended nanobeams, but have so far exhibited weaker vacuum optomechanical coupling rates, leaving a trade-off between coupling strength and thermal robustness. Here, we largely close this gap: we design and experimentally demonstrate a release-free silicon optomechanical crystal with a record vacuum optomechanical coupling rate of about g_OM / (2 π) = 800 kHz, comparable to suspended state-of-the-art devices. The resulting optomechanical scattering rate Γ_OM/(2 π)= 1.1 kHz is nearly twice that of previous release-free implementations. This performance is achieved by combining physics-guided human intuition with a multiphysics inverse-design algorithm introduced here for resonant optomechanical structures. Beyond the specific device demonstrated, the inverse-design framework is applicable to co-optimizing optical and mechanical resonances and eigenmodes more broadly. These results strengthen release-free optomechanical crystals as a platform for fast, low-noise classical and quantum optomechanics.

Piezo-optomechanical quantum transducers are poised to marry the strengths of optical photons with those of superconducting qubits. We present first experimental results on a novel release-free transducer architecture with large thermal contact area to the substrate.

Electro-optic modulation is central to classical optical communications and emerging quantum technologies. High-confinement optomechanical crystal modulators enable microwave-optical transduction through strong optomechanical interactions and offer a promising interface between superconducting qubits and optical fibers. However, their performance is limited by thermal noise from optical absorption. Release-free optomechanical crystals provide improved thermal anchoring but have not yet been integrated into a microwave-optical transducer. Here, we demonstrate a release-free electro-optomechanical transducer combining strong optomechanical interactions in silicon with the efficient piezoelectricity of lithium niobate via micro-transfer printing. We observe electro- and optomechanical coupling rates compatible with quantum-level operation when co-integrated with a superconducting microwave circuit. This advance moves release-free electro-optomechanical devices toward practical microwave-optical interfaces.

Phonons hold promise for storing and transferring quantum information, including in mechanically-mediated quantum interconnects between superconducting qubits and light. Phononic crystal cavities confine gigahertz sound to micron-scale volumes well matched to near-infrared light. So far, these devices have typically been suspended to suppress phononic radiation loss into the substrate, but suspension limits thermal anchoring leading to excess noise. Release-free phononic crystals have emerged as a way to address this challenge – but had yet to be shown compatible with strong electromechanical interactions. Here, we demonstrate a release-free phononic crystal cavity strongly coupled to a high-impedance microwave resonator, with an electromechanical coupling rate g_em/(2π) ≈ 30 MHz that exceeds both the mechanical and microwave loss rates, leading to a cooperativity up to 𝒞≈ 180 on resonance. In addition, our lithium niobate phononic crystals reach quality factors above 10^4 at millikelvin temperature on both silicon and sapphire substrates. Our results establish release-free phononic crystals as compact, scalable interfaces between microwaves and gigahertz sound for emerging sensing, communication, and computing systems.

We present cryogenic measurements of release-free silicon optomechanical crystals (OMC), focusing on resilience to optical absorption heating. Our device sustains near-unity phonon occupation at 35 dB higher intracavity optical energy compared to a suspended OMC.

Quantum transduction between microwave and optical photons offers the potential to merge the long-range connectivity of optical photons with the deterministic quantum operations of superconducting microwave qubits. A promising approach to achieving this uses an intermediary mechanical mode along with piezo-optomechanical interactions. Traditionally, these transducers are suspended to confine mechanical fields, but this complicates manufacturing and comes with the major challenge of poor thermal anchoring and a trade-off between noise and efficiency. To overcome these issues, we introduce the—to our knowledge—first design of a release-free electro-optomechanical quantum transducer. Our release-free, i.e., non-suspended, design leverages a silicon-on-sapphire platform. It combines release-free lithium niobate electromechanical crystals with silicon optomechanical crystals on a sapphire substrate, optimizing thermal anchoring and microwave and mechanical coherence. Despite departing from the traditional suspended transducer paradigm, our release-free design achieves coupling rates sufficient for quantum-level interactions between microwave photons, phonons, and optical photons. Unconventionally, it utilizes high-wavevector mechanical modes tightly confined to the chip surface. Beyond quantum science and engineering, this platform and its design principles could also propel low-power acousto-optic systems in integrated photonics.

We report early results on inverse-designed release-free optomechanical crystals, a possible path to thermally robust microwave-to-optics transducers. We demonstrate the, to our knowledge, highest vacuum optomechanical interaction rate for release-free systems at 770 kHz.

Lithium niobate (LN) is a promising material for complex photonic‐electronic circuits with wide applications in fields like data communications, sensing, optical computation, and quantum optics. There is a great step toward LN photonic integrated circuits (PICs) with the development of dry etching for low‐loss LN on insulator (LNOI) waveguides. However, the versatility of the LN waveguide platform for applications like nonlinear devices and passive phase sensitive components, has not been fully utilized. Two significant challenges are the difficulty of making highly confined ultralow‐loss waveguides and overcoming the strong material birefringence. Here a fabrication technology is developed for an ultralow‐loss, tightly‐confined, dispersion‐engineered LN waveguide. An ultra‐low propagation loss of 5.8 dB/m is demonstrated in a decimeter‐long LN spiral waveguide. This study is focused on Z‐cut LN waveguides with TE mode to avoid the material birefringence. Aiming for nonlinear applications, it is demonstrated that the first all normal‐dispersion (ANDi) based coherent octave‐spanning supercontinuum frequency comb in integrated LN waveguide. This ultralow‐loss Z‐cut LN long waveguide might be useful in on‐chip narrow linewidth lasers, optical delay lines, and parametric amplifiers.

Interaction between light and high-frequency sound is a key area in integrated photonics, quantum and nonlinear optics, and quantum science. However, the typical suspended optomechanical structures suffer from poor thermal anchoring, making them susceptible to thermal noise arising from optical absorption. Here, we demonstrate a chip-scale, release-free silicon optomechanical crystal cavity (OMC) operating cryogenically with improved resilience to laser light. Relative to a suspended nanobeam OMC, we observe an 18 dB suppression of the thermo-optic effect, and the device sustains near-unity phonon occupation at 35 dB higher intracavity optical energy. Time-resolved measurements further reveal rapid initial thermalization governed by the mechanical decay time. With further material and design improvements in sight, these results bolster release-free systems on a chip as a path for low-noise and high-power classical and quantum electro-optomechanics, such as for frequency converters between microwave and optical photons.

Exploiting the strengths of different quantum hardware components may enhance the capabilities of emerging quantum processors. Here, we propose and analyze a quantum architecture that leverages the non-local connectivity of optics, along with the exquisite quantum control offered by superconducting microwave circuits, to produce entangled optical resource states. Contrary to previous proposals on optically distributing entanglement between superconducting microwave processors, we use squeezing between microwaves and optics to produce microwave-optical Bell pairs in a dual-rail encoding from a single microwave quantum processor. Moreover, the microwave quantum processor allows us to deterministically entangle microwave-optical Bell pairs into larger cluster states, from which entangled optical photons can be extracted through microwave measurements. Our scheme paves the way for small microwave quantum processors to create heralded entangled optical resource states for optical quantum computation, communication, and sensing using imperfect microwave-optics transducers. We expect that improved isolation of the superconducting processor from stray optical fields will allow the scheme to be demonstrated using currently available hardware.

Lithium niobate (LN) is a promising material among integrated photonics, with applications like high-speed EO modulators, frequency combs, frequency converters, and photon-pair sources [1]. Increasing the system complexity of LN integrated circuits requires large-scale arrays of photonic components [2]. Therefore, an ideal integrated LN waveguide platform should allow dense integration, low propagation losses, and exhibit low fabrication complexity.

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 prevents heat-carrying noise phonons from rapidly leaking away. Thermal anchoring 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 new class of clamped OMCs realizing -- for the first time -- 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 $g_0/(2\pi) \approx 0.50$ MHz 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 a new avenue using clamped OMCs in both classical and quantum communications, sensing, and computation through scalable mechanical circuitry that couples strongly to light.

A quantum network that distributes and processes entanglement would enable powerful new computers and sensors. Optical photons with a frequency of a few hundred terahertz are perhaps the only way to distribute quantum information over long distances. Superconducting qubits on the other hand, which are one of the most promising approaches for realizing large-scale quantum machines, operate naturally on microwave photons that have roughly $40,000$ times less energy. To network these quantum machines across appreciable distances, we must bridge this frequency gap and learn how to generate entanglement across widely disparate parts of the electromagnetic spectrum. Here we implement and demonstrate a transducer device that can generate entanglement between optical and microwave photons, and use it to show that by detecting an optical photon we add a single photon to the microwave field. We achieve this by using a gigahertz nanomechanical resonance as an intermediary, and efficiently coupling it to optical and microwave channels through strong optomechanical and piezoelectric interactions. We show continuous operation of the transducer with $5\%$ frequency conversion efficiency, and pulsed microwave photon generation at a heralding rate of $15$ hertz. Optical absorption in the device generates thermal noise of less than two microwave photons. Joint measurements on optical photons from a pair of transducers would realize entanglement generation between distant microwave-frequency quantum nodes. Improvements of the system efficiency and device performance, necessary to realize a high rate of entanglement generation in such networks are within reach.

Lithium niobate (LN) is a promising material for future complex photonic-electronic circuits, with wide applications in fields like communications, sensing, quantum optics, and computation. LN took a great stride toward compact photonic integrated circuits (PICs) with the development of partially-etched LN on insulator (LNOI) waveguides. However, integration density is still limited for future high-compact PICs due to the partial edge nature of their waveguides. Here, we demonstrate a fully-etched LN PIC platform which, for the first time, simultaneously achieves ultra-low propagation loss and compact circuit size. The tightly-confined fully-etched LN waveguides with smooth sidewalls allow us to bring the bending radius down to 20 $\mu$m (corresponds to 1 THz FSR). We have achieved compact high-$Q$ microring resonators with $Q/V$ of 7.1 $\times$ 10$^{4}$ $\mu$m$^{-3}$, almost one order of magnitude larger than previous demonstrations. The statistical mean propagation losses of our LN waveguides is 8.5 dB/m (corresponds to mean $Q$-factor of 4.9 $\times$ 10$^{6}$) even with a small bending radius of 40 $\mu$m. Our compact and ultra-low-loss LN platform shows great potential in future miniaturized multifunctional integration systems. As complementary evidence to show the utility of our platform, we demonstrate soliton microcombs with an ultra-high repetition rate of 500 GHz in LN.

Interconnecting distant superconducting quantum processors requires optical links. Here, we demonstrate a transducer that generates entangled pairs of microwave and optical photons, achieving a heralding rate of 15 Hz with two added noise photons.

Lithium niobate (LN) is a promising material for future complex photonic-electronic circuits, with wide applications in such fields as communications, sensing, quantum optics, and computation. LN took a great stride toward compact photonic integrated circuits (PICs) with the development of partially etched LN on insulator (LNOI) waveguides. However, integration density is still limited for future highly compact PICs, owing to the partial etching nature of their waveguides. Here, we demonstrate a fully etched LN PIC platform, which, for the first time to our knowledge, simultaneously achieves ultralow propagation loss and compact circuit size. The tightly confined fully etched LN waveguides with smooth sidewalls allow us to bring the bending radius down to 20 μm (corresponding to 1 THz free spectral range). We have achieved compact high Q microring resonators with Q/V of 8.7 × 104 μm-3, almost one order of magnitude larger than previous demonstrations. The statistical mean propagation losses of our LN waveguides is 8.5 dB/m (corresponding to a mean Q factor of 4.9 × 106), even with a small bending radius of 40 μm. Our compact and ultralow-loss LN platform shows great potential in future miniaturized multifunctional integration systems. As complementary evidence to show the utility of our platform, we demonstrate soliton microcombs with an ultrahigh repetition rate of 500 GHz in LN.

Cavity optomechanics and Brillouin scattering have historically developed as separate fields of study, focused on distinct optoacoustic interaction effects, and realized in different physical platforms. These gaps are now closing rapidly, as researchers embrace the fundamental similarities between the two fields. Both fields study the three-wave mixing between electromagnetic and acoustic waves. Here, we review this convergence by showing how optoacoustic platforms increasingly blur the traditional distinctions between cavity optomechanics and Brillouin scattering. We discuss how the theoretical formalisms used by the two communities can be directly mapped between each other in both waveguides and cavities.

Intensity modulators are an essential component in optics for controlling free-space beams. Many applications require the intensity of a free-space beam to be modulated at a single frequency, including wide-field lock-in detection for sensitive measurements, mode-locking in lasers, and phase-shift time-of-flight imaging (LiDAR). Here, we report a new type of single frequency intensity modulator that we refer to as a longitudinal piezoelectric resonant photoelastic modulator. The modulator consists of a thin lithium niobate wafer coated with transparent surface electrodes. One of the fundamental acoustic modes of the modulator is excited through the surface electrodes, confining an acoustic standing wave to the electrode region. The modulator is placed between optical polarizers; light propagating through the modulator and polarizers is intensity modulated with a wide acceptance angle and record breaking modulation efficiency in the megahertz frequency regime. As an illustration of the potential of our approach, we show that the proposed modulator can be integrated with a standard image sensor to effectively convert it into a time-of-flight imaging system.

We demonstrate that coating with a thin blanket layer reduces the propagation loss of silicon nitride dispersion-engineered waveguides featuring strong optical field confinement.