Matt Eichenfield

Realizing photonic quantum computing at scale requires integrated circuits that combine ultra-low loss with fast, low-power, low-hysteresis, and low-crosstalk reconfiguration. These requirements are particularly challenging at visible wavelengths, where many quantum resource-state generators, including single-photon sources and quantum memories, naturally operate. Low-confinement silicon nitride waveguides offer the requisite loss performance, but conventional thermo-optic modulators dissipate significant static power, driving thermal crosstalk and precluding cryogenic operation. Visible-wavelength piezo-optomechanical circuits avoid these drawbacks, but existing demonstrations rely either on high-confinement waveguides with propagation losses of 35-100 dB/m, or on low-confinement platforms using foundry-incompatible lead zirconate titanate (PZT). Here we combine piezo-optomechanical actuation with a CMOS-foundry-fabricated, low-confinement silicon nitride platform, achieving 2.6 dB/m propagation loss at 780 nm, megahertz-scale modulation bandwidth, a half-wave voltage-length product of 2.8 V ⋅ m, and negligible hysteresis. We demonstrate reconfigurable Mach-Zehnder interferometers with 0.63 dB loss per spiral phase shifter, enabling deep, actively reconfigurable visible-wavelength quantum photonic circuits.

We demonstrate heterogeneous integration of 5 µm-thick Y-cut lithium niobate (LN) films onto 2 µm-thick yttrium iron garnet (YIG) on gadolinium gallium garnet (GGG) via bonding and substrate removal, producing large, void-free active areas. The LN-on-YIG heterostructure enables low-loss acoustic waveguiding while maintaining sufficient strain-mediated coupling to spin waves in the buried YIG. Using this platform, we realize surface acoustic wave delay devices and observe acoustic-driven magnetic resonance at 655 MHz, with 6.66 dB/mm absorption and a − 44°/mm phase shift. Spatially resolved laser Doppler vibrometry further shows a magnetic field-dependent long-wavelength modulation of the propagating acoustic wave, possible evidence of driven energy exchange between the acoustic and magnetic spin system. These results establish heterogeneous integration as a wafer-scalable route to low-loss magnetoacoustic devices that combine high-performance piezoelectrics with ultralow-damping magnetic insulators, eliminating the need for lattice matching.

Acceleration sensing underlies a wide range of commercial and scientific technologies, yet optomechanical accelerometers, despite their impressive displacement sensitivity, have not reached practical viability for commercial or defense applications. Most optomechanical sensors are sensitive to external non-inertial forces, vibrations, temperature drift, and wavelength drift. In the case of the photonic integrated optomechanical accelerometers, these effects are primary sources of bias instability and limit the ability of these sensors to attain navigation-grade performance. We present a photonic integrated, fiber-packaged optomechanical accelerometer that advances toward navigation-grade accelerometry, especially with regard to bias instability. Displacement readout is provided by an integrated differential strain-sensing Mach–Zehnder interferometer attached to an ultra-rigid, bulk-micromachined proof mass with a 93.4 kHz fundamental resonance frequency (22.5 pm/g displacement). The high displacement sensitivity provides a 4.2 μg/Hz acceleration resolution over a 66 kHz operational bandwidth. Furthermore, we show that the combination of high rigidity and intrinsic differential optical readout makes the device insensitive to the common causes of bias instability, and we measure a bias instability of 6.3 μg at 243 s. The device operates over a temperature range of greater than 20 °C and a 17 nm optical bandwidth, eliminating the need for sophisticated laser sources, providing a pathway to reduced size, weight, and power. Our device is well suited for operation in practical environments and establishes a pathway for chip-scale optomechanical accelerometers to approach and potentially surpass the performance of existing chip-scale accelerometer platforms.

Next-generation photonic architectures for AI, sensing, and quantum computing require thousands to millions of reprogrammable photonic devices on a chip ¹ . The monolithic integration of Electronically-backed Photonic Integrated Circuits (EPICs) allows for very high density electrical interconnection and electronic drivers that can scale with photonics. Piezo-optomechanical photonic integrated circuits (POMPICs) offer low power consumption, high speed modulation, cryogenic compatibility and broadband optical transparency from ultraviolet to infrared wavelengths ^2,3 , but have not been demonstrated with monolithically integrated CMOS electronics. Here, we show a fully monolithic, all-CMOS fabricated platform for POMPICs co-fabricated with commercial control electronics. 200 millimeter photonic wafers are constructed directly on completed CMOS driver wafers by back-end-of-line processing, connecting integrated piezoelectric actuators under broadband silicon nitride waveguides to a high-density digital backplane comprising >2 million electrical connections per die with 6.4×6.4 micron electrode pitch. We introduce segmented POMPIC components as Photonic Digital-to-Analog converters (PDACs) that convert low-voltage digital electronic signals to multi-bit analog optical phase and amplitude modulation, and we demonstrate parallel control of optical phase shifters, Mach-Zehnder interferometers, optical routing trees, and tunable ring resonators using a standard HDMI interface to program CMOS electronics. We test multiple reticles and perform electronic and photonic characterization across the entire wafer to establish uniformity and yield, demonstrating wafer-scale integration of POMPICs on an electronic backplane and enabling dense, scalable electronic control of piezo-optomechanical circuits. This architecture provides a path to tightly integrated, high-channel-count control of quantum and classical piezo-optomechanical photonic integrated circuits, supporting applications in linear optical quantum computing, hybrid quantum systems with solid-state emitters, photonic neural networks, quantum networking, and display technologies.

Surface acoustic wave platforms based on piezoelectric thin-film heterostructures provide sub-wavelength acoustic confinement, making them attractive for compact nonlinear phononic systems with applications including frequency conversion, parametric interactions, and nonlinear signal processing. Here, we investigate guided surface acoustic wave phononic four-wave mixing at gigahertz frequencies in an aluminum scandium nitride (Al0.58Sc0.42N)/4H–silicon carbide heterostructure operated at both room temperature (295 K) and cryogenic temperature (4 K). The 500-nm thick aluminum scandium nitride film supports guided Rayleigh and Sezawa modes with distinct displacement and strain energy density distributions, allowing a direct comparison of mode-dependent nonlinear behavior within the same device. Continuous-wave four-wave mixing measurements reveal an enhancement in the extracted modal nonlinear coefficient at 4 K relative to 295 K for both modes. In addition, the Rayleigh mode exhibits a modal nonlinearity approximately two orders of magnitude larger than that of the Sezawa mode across both temperature regimes. These results demonstrate that phononic four-wave mixing is strongly influenced by temperature, mode confinement, and strain localization while establishing aluminum scandium nitride on silicon carbide heterostructures as a promising platform for engineering enhanced nonlinear phononic interactions for future classical and quantum acoustic on-chip signal processing systems.

The stringent demands of photonic quantum computing protocols motivate photonic integrated circuit (PIC) platforms with passive optical properties such as extremely low losses and correspondingly large circuit depths, as well as active optical properties such as high reconfiguration rates, low power dissipation, and minimal crosstalk. At the same time, many quantum photonic resource state generators, such as single-photon sources and quantum memories, require operation in the visible wavelength range. These requirements make the passive optical properties of CMOS-fabricated, ultralow-loss, low-confinement silicon nitride waveguides especially attractive. However, the conventional active properties of these systems based on thermo-optic modulation are plagued by high levels of crosstalk, slow modulation rates, and high power dissipation. Although there have been recent demonstrations of CMOS-fabricated, visible wavelength, piezo-optomechanical PICs that solve the above challenges associated with implementing active functionality, these have made use of high-confinement waveguides with currently demonstrated losses of order 0.3–1 dB/cm, precluding circuit depths required for scalable quantum algorithms. Here, we demonstrate that combining piezo-optomechanical actuation with a low-confinement, ultra-low loss silicon nitride platform addresses the scalability challenge while enabling high-performance active functionality at visible wavelengths. This platform achieves a propagation loss 0.026 dB/cm at 780 nm, modulation bandwidths in the MHz range, and a phase shifter voltage-length product (VπL) of approximately 2.8 V · m and negligible hysteresis. We further demonstrate reconfigurable Mach-Zehnder interferometers based on spiral phase shifters with 0.63 dB loss per phase shifter.

A seamless chip-to-world photonic interface enables broad advancements in optical ranging, display, communication, computation and quantum information science. The ideal solution enables two-dimensional scanning of a diffraction-limited beam from anywhere on a photonic integrated circuit to a large number of resolvable spots. Current beam-scanning technologies are limited by a fundamental trade-off: photonic-integrated-circuits with diffractive optics offer scalability but have poor mode quality^1,2, whereas inertially limited micromechanical scanners provide high-quality beams but lack scalable integration^3,4. Here we report a photonic ski-jump—a nanoscale waveguide monolithically integrated on a piezoelectric cantilever—to overcome these limitations. It passively curls ~90° out-of-plane within a less-than-0.1 mm² footprint, emits a submicrometre, broadband diffraction-limited beam, and exhibits kilohertz-rate mechanical resonances with quality factors of over 10,000. Fabricated in a volume complementary metal–oxide–semiconductor (CMOS) foundry, our device enables scalable two-dimensional beam scanning. Driven on-resonance at CMOS-level voltages, it achieves a footprint-adjusted spot rate of 68.6 mega spots s^–1 mm^–², exceeding state-of-the-art micro-electro-mechanical systems mirrors by more than 50-fold, which is sufficient for one million pixels at 100 Hz from an approximately 1.5 mm diameter footprint. We demonstrate full-colour image and video projection, and single-photon initialization and readout from silicon vacancy centres in diamond. Finally, by demonstrating uniformity across a 64 ski-jump array, we establish a pathway to achieving greater than one gigaspot resolution at kilohertz rates within a sub-5-cm-diameter footprint, creating a seamless optical pipeline between integrated photonic processors and the free-space world.

Programmable photonic integrated circuits (PICs) have recently emerged as an important technology for quantum information science and artificial neural networks. In particular, PICs with microelectromechanical-based modulators have the advantages of voltage-based control, ultra-low-energy consumption, cryogenic compatibility, and CMOS-foundry support. Here, we report a cantilever optical modulator that utilizes hybrid piezoelectric and electrostatic tuning forces together on a monolithic silicon nitride (SiN) PIC platform. The device achieves actuation of visible-wavelength light with quasi-static tuning up to 10 kHz at 1.5 Vπ-cm as well as high-speed (>20 MHz) AC modulation with dynamically adjustable (25–40 MHz) mechanical resonances. We report the physics of how geometric nonlinearities, such as capacitive pull-in, give rise to suspended and contacted cantilever modes. These reversible operating regimes generate different strain profiles and boundary conditions, which are responsible for the active tuning of the mechanical resonances. Our proof-of-concept electrostatic–piezo modulator shows promising potential in large-scale programmable PICs applied to high-speed optical switching and optomechanical sensing.

Surface acoustic waves (SAWs) enable a wide array of technologies, including radiofrequency filters^1,2, chemical and biological sensors^3,4,5, acousto-optic devices^6,7,8, acoustic control of microfluidic flow in lab-on-a-chip systems^9,10,11 and quantum phononics^{12,13,14,15,16,17,18,19}. Although numerous methods exist for generating SAWs, they each have intrinsic limitations that inhibit performance, operation at high frequencies and use in systems constrained in size, weight and power. Here we present a completely solid-state, single-chip SAW phonon laser consisting of a lithium niobate SAW resonator with an internal, d.c. electrically injected and broadband semiconductor gain medium with 2 footprint. Below the threshold bias of 36 V, the device behaves as a resonant amplifier, and above it exhibits self-sustained coherent oscillation, linewidth narrowing and high output powers. A continuous on-chip acoustic output power of up to −6.1 dBm is generated at 1 GHz with a resolution-limited linewidth of −1 at 1 kHz offset. Through detailed modelling, we show pathways for improving the performance of these devices, including mHz linewidths, high power efficiencies and footprints under 550 μm² at 10 GHz. This demonstration paves the way for ultrahigh-frequency SAW sources on-chip and highly miniaturized SAW-based systems that can be operated without an external radiofrequency source.

We analytically and experimentally show how voltage modulation of a microfabricated piezo-optomechanical magnetic field sensor improves performance at Super Low Frequencies, an especially important frequency range not currently served by microfabricated optomechanical magnetometers.