Evelyn L. Hu

4H-silicon carbide is a promising platform for solid-state quantum technology due to its commercial availability as a wide bandgap semiconductor and ability to host numerous spin-active color centers. Integrating color centers into suspended nanodevices enhances defect control and readout, key advances needed to fully harness their potential. However, challenges in developing robust fabrication processes for 4H-SiC thin films, due to the material's chemical and mechanical stability, limit their implementation in quantum applications. Here, we report on a new fabrication approach that first synthesizes suspended thin films from a monolithic platform and then patterns devices. With this technique, we fabricate and characterize structures tailored for defect integration, demonstrating 1D photonic crystal cavities, with and without waveguide interfaces, and lithium niobate on 4H-SiC acoustic cavities. This approach allows for greater fabrication flexibility, supporting high temperature annealing and heterogeneous material platform compatibility, providing a versatile platform for scalable fabrication of 4H-SiC devices for quantum technologies.

Abstract Iron oxide (Fe 3 O 4 ) has attracted significant attention as a promising anode material for sodium‐ion batteries (SIBs) due to its natural abundance, environmental benignity, and high theoretical capacity of 926 mA h g −1 . Nevertheless, its practical application is limited by intrinsic drawbacks, including low electrical conductivity, sluggish Na⁺ diffusion kinetics, and severe volume variation during cycling, leading to rapid capacity fading and poor rate capability. To address these issues, a novel Fe 3 O 4 /Fe@N‐doped carbon (Fe 3 O 4 /Fe@CN) nanostructure is rationally designed, which integrates Fe 3 O 4 /Fe homogeneous heterojunctions with a uniform nitrogen‐doped carbon shell. The built‐in electric field at the Fe‐Fe 3 O 4 interface promotes charge redistribution and accelerates electron/ion transport, while the N‐doped carbon shell enhances electrical conductivity and buffers mechanical stress during sodiation/desodiation processes. Benefiting from this synergistic structure, the Fe 3 O 4 /Fe@CN anode delivers a high reversible capacity of 336.9 mA h g −1 at 0.1 A g −1 , excellent rate capability with 244.7 mA h g −1 at 2 A g −1 , and remarkable cycling stability, retaining 76.4% capacity after 500 cycles. Furthermore, a full cell assembled with a Na 3 V 2 (PO 4 ) 3 cathode exhibits a high energy density of 112.67 Wh·kg −1 at 51.42 W·kg −1 and outstanding cycling performance. This study offers a versatile strategy to unlock the potential of Fe 3 O 4 for high‐performance SIB anodes through heterojunction and interfacial engineering.

This study investigates the design and performance of a Vertical Axis Wind Turbine (VAWT), which uses the S809 airfoil for blade design and employs 3D printing for blade fabrication. Performance testing is conducted in a Low-Speed Wind Tunnel (LSWT) to evaluate the turbine’s power output under varying rotational speeds. Experimental results show a wind speed of 9.51 m/s, the maximum power output of the generator reached 450 mW. Therefore, 3D printing has the potential to develop wind turbine components for renewable energy technology.

In the original Letter, the value for the thickness of each slab was mistakenly reported as 0.54a; the correct value is 0.35a.

This paper proposes a circularly polarised (CP) microstrip antenna array featuring irregularly configured J-shaped magneto-electric (ME) dipoles. Each antenna element consists of a set of similarly shaped J-shaped irregular patches sand a set of similarly shaped rectangular irregular patches.These patches couple energy to four metallised apertures (serving as magnetic dipoles) through a unique H-shaped slot, which then transfers the energy to the J-shaped radiating patches (electric dipoles), thereby generating the rotating electric field necessary for CP radiation, resulting in left-handed circularly polarised (LHCP) waves. By arranging the designed antenna elements into a 4 × 4 array and adopting sequential rotation feeding (SRF), the array achieves an impedance bandwidth (IBW) of 53.2% (21.73–37.48 GHz) and an axial ratio (AR) bandwidth of 48.71% (22.8–37.48 GHz). Within the AR bandwidth range, it exhibits a peak gain of 17.75 dBic and stable gain. The average radiation efficiency exceeds 80%, and the overall size is 4.83λ0 × 5.05λ0 × 0.17λ0. This antenna array boasts wide impedance and AR bandwidths, ease of integration, and many other advantages, making it suitable for a wide range of applications in millimetre-wave(mmW) communication systems.

Dynamic control of a material’s optical properties lays the groundwork for reconfigurable flat optical devices, tunable devices that can learn from optical inputs, and energy-efficient chip-scale communications and computation platforms that promise to reduce the energy consumption of the modern telecommunications infrastructure. One appealing method to achieve this relies on electro-optics, which provides a direct connection between driving electronics and optical properties of materials. Integrating electro-optic materials into micro and nanostructures heralds a new generation of devices with light-matter-microwave interactions much stronger than bulk devices, creating a platform for unprecedented photonic devices. This presentation will highlight integrated photonic devices based on Lithium Niobate on Insulator, including femtosecond optical pulse generation driven by dispersion engineering and microwave modulation. I will conclude the presentation with some work establishing the fundamental processing-performance relationships that give rise to low frequency instability in the device platform, enabling a new generation of compact, ultra-stable photonic switches.

Background: Severe autoimmune encephalitis (AE) can cause significant neurological deficits, status epilepticus, status dystonicus, and even death, which can be life-threatening to patients. Accurate risk stratification for severe AE progression is critical for optimizing therapeutic strategies. The comprehensive prediction models for severe AE based on routine clinical data and laboratory indicators remain lacking. Objective: To develop and validate a prediction model for severe AE to optimize individualized treatment. Methods: We collected clinical data and laboratory examination results from 207 patients with confirmed AE. The study population was divided into development and validation cohort. A prediction model for severe AE was constructed using a nomogram and was rigorously validated both internally and externally. Severe AE was defined as modified Rankin Scale (mRS) > 2 and Clinical Assessment Scale for Encephalitis (CASE) > 4. Results: The variables ultimately included in the nomogram for the severe AE predictive model were age, psychiatric and/or behavioral abnormalities, seizures, decreased level of consciousness, cognitive impairment, involuntary movements, autonomic dysfunction, and increased intrathecal IgG synthesis rate. It demonstrated excellent discriminative capacity and calibration through internal-external validation. Conclusion: The prediction model has highly feasibility in clinical practice, and holds promise as an important tool for risk assessment and guiding individualized treatment in patients with AE.

Silicon carbide (SiC) is a semiconductor used in quantum information processing, microelectromechanical systems, photonics, power electronics, and harsh environment sensors. However, its high-temperature stability, high breakdown voltage, wide bandgap, and high mechanical strength are accompanied by a chemical inertness, which makes complex micromachining difficult. Photoelectrochemical (PEC) etching is a simple, rapid means of wet processing SiC, including the use of dopant-selective etch stops that take advantage of the mature SiC homoepitaxy. However, dopant-selective PEC etching typically relies on highly doped material, which poses challenges for device applications such as quantum defects and photonics that benefit from low doping to produce robust emitter properties and high optical transparency. In this work, we develop a selective PEC process that relies not on high doping but on the electrical depletion of a fabricated diode structure, allowing the selective etching of an n -doped substrate wafer versus an undoped epitaxial (carrier density of 1(10) 14 cm –3 ) device layer. We characterize the photoresponse and PEC behavior of the diode under bias and use those insights to suspend large (100 × 100 μm) undoped membranes of SiC. We further characterize the compatibility of membranes with quantum emitters, performing comparative spin spectroscopy between undoped and highly doped membrane structures, finding the use of undoped material improves ensemble spin lifetime by >5×. This work enables the fabrication of high-purity suspended thin films suitable for scalable photonics, mechanics, and quantum technologies in SiC.

Solid-state defect quantum systems are exquisite probes of their local charge environment. Nonlinear dynamical electric fields in solids are challenging to characterize directly, conventionally limited to coarse macroscopic methods which fail to capture subtle effects in the material. Here, through transient optical spectroscopy on an embedded T center ensemble, we realize the in-situ observation of a silicon PIN-diode phase transition to a regime of self-sustained carrier oscillatory dynamics characteristic of negative differential resistance. Manifest in both the ensemble electroluminescence and photoluminescence, we find a temperature and field-dependent phase space for persistent undamped amplitude oscillations indicative of a collective ensemble response to the field dynamics. These findings shed new light on the cryogenic behavior of silicon, provide fundamental insight into the physics of the T center for improved quantum device performance, and open a promising new direction for defect-based local quantum sensing in semiconductor devices.

Moiré photonics has become a burgeoning research field with many potential applications, one being a new kind of nanoscale, actively tunable semiconductor laser. Stacked bilayer photonic crystal lasers provide possibilities in active tuning using multiple degrees of freedom, including the twist angle and coupling distance between the two layers. Initial demonstrations of moiré photonic crystal lasers with embedded gain material have been shown in devices where the two layers are “merged” into a single layer; however, to fully realize the promise of moiré lasers’ tunability, true bilayer systems must be explored. We demonstrate a fabrication protocol to realize this kind of laser in gallium nitride with embedded indium gallium nitride emitters. We discuss fabrication challenges, including rotational precision, membrane adhesion, and material strain, as well as initial photoluminescent characterization. This research elucidates design questions and limitations that are critical for moving towards novel, tunable, low-threshold lasers in the visible regime.

Silicon carbide (SiC) is a semiconductor used in quantum information processing, microelectromechanical systems, photonics, power electronics, and harsh environment sensors. However, its high temperature stability, high breakdown voltage, wide bandgap, and high mechanical strength are accompanied by a chemical inertness which makes complex micromachining difficult. Photoelectrochemical etching is a simple, rapid means of wet processing SiC, including the use of dopant selective etch stops that take advantage of mature SiC homoepitaxy. However, dopant selective photoelectrochemical etching typically relies on highly doped material, which poses challenges for device applications such as quantum defects and photonics that benefit from low doping to produce robust emitter properties and high optical transparency. In this work, we develop a new, selective photoelectrochemical etching process that relies not on high doping but on the electrical depletion of a fabricated diode structure, allowing the selective etching of an n-doped substrate wafer versus an undoped epitaxial ($N_a=1(10)^{14}cm^{-3}$) device layer. We characterize the photo-response and photoelectrochemical etching behavior of the diode under bias and use those insights to suspend large ($>100μm^2$) undoped membranes of SiC. We further characterize the compatibility of membranes with quantum emitters, performing comparative spin spectroscopy between undoped and highly doped membrane structures, finding the use of undoped material improves ensemble spin lifetime by $>3x$. This work enables the fabrication of high-purity suspended thin films suitable for scalable photonics, mechanics, and quantum technologies in SiC.

Silicon color centers have emerged as promising candidates for quantum information technologies, yet their interaction with electric fields is not well understood. We will discuss electrical manipulation of G-centers in silicon -- quantum emitters that photoluminesce in the telecom O-band. We fabricated lateral electrical diodes with an integrated ensemble of G centers in a commercial silicon on insulator wafer. Under application of a reverse-biased DC electric field, the ensemble of G-centers redshifts by approximately 1.4 GHz/V above a threshold “turn-on voltage.” The fluorescence intensity is modulated by increasing electric field, ultimately achieving 100% extinction. Finally, we use G center fluorescence to directly image the electric field distribution within the devices, obtaining insight into the spatial and voltage-dependent variation of the junction depletion region and the associated mediating effects on the ensemble. The emitter-field coupling is correlated to the photocurrent generated in the device. Our device architecture uniquely enables simultaneous optical and electrical manipulation of quantum emitters, and it is readily extensible to other quantum emitters.

Silicon color centers have recently emerged as promising candidates for commercial quantum technology, yet their interaction with electric fields has yet to be investigated. In this paper, we demonstrate electrical manipulation of telecom silicon color centers by implementing novel lateral electrical diodes with an integrated G center ensemble in a commercial silicon on insulator wafer. The ensemble optical response is characterized under application of a reverse-biased DC electric field, observing both 100% modulation of fluorescence signal, and wavelength redshift of approximately 1.24 ± 0.08 GHz/V above a threshold voltage. Finally, we use G center fluorescence to directly image the electric field distribution within the devices, obtaining insight into the spatial and voltage-dependent variation of the junction depletion region and the associated mediating effects on the ensemble. Strong correlation between emitter-field coupling and generated photocurrent is observed. Our demonstration enables electrical control and stabilization of semiconductor quantum emitters.

<title>Abstract</title> Moiré photonic structures permit the engineering of optical band structures and light-matter interactions, offering new opportunities in photonics and optoelectronics, paving the way for new nanophotonic applications, such as ultra-low threshold lasing and versatile nonlinear and quantum light sources. Until now, however, the lack of in situ tunability has limited the potential of these structures. For example, the lack of control of the twist angle poses challenges for high-resolution material spectroscopy and the development of new applications that require moiré optical properties. In this paper we present a MEMS-integrated twisted moiré photonic-crystal sensor with tunable interlayer distance and twist angle. The MEMS actuators modulate the wavelength and polarization resonances of the photonic crystal sensor via a twist- and gap-tuned moiré scattering effect. Using a reconstruction algorithm, this chip-based sensor can be used to simultaneously resolve the spectrum and polarization state of a wide-band signal in the telecom range and the full Poincaré sphere. We also demonstrate hyperspectral and hyperpolarimetric imaging using this single sensor. Our research illustrates some of the remarkable applications of multidimensional control of degrees of freedom in twisted moiré photonic platforms and establishes a scalable pathway towards creating comprehensive flat-optics devices suitable for versatile light manipulation and information processing.

Metasurfaces and photonic crystals have revolutionized classical and quantum manipulation of light and opened the door to studying various optical singularities related to phases and polarization states. However, traditional nanophotonic devices lack reconfigurability, hindering the dynamic switching and optimization of optical singularities. This paper delves into the underexplored concept of tunable bilayer photonic crystals (BPhCs), which offer rich interlayer coupling effects. Utilizing silicon nitride-based BPhCs, we demonstrate tunable bidirectional and unidirectional polarization singularities, along with spatiotemporal phase singularities. Leveraging these tunable singularities, we achieve dynamic modulation of bound-state-in-continuum states, unidirectional guided resonances, and both longitudinal and transverse orbital angular momentum. Our work paves the way for multidimensional control over polarization and phase, inspiring new directions in ultrafast optics, optoelectronics, and quantum optics.

This paper explores tunable bilayer photonic crystals (BPhCs) for dynamic control of optical singularities, demonstrating bidirectional/unidirectional polarization, and spatiotemporal phase singularities. This study enables multidimensional control in ultrafast and quantum optics.

Reconfigurable optics, optical systems that have a dynamically tunable configuration, are emerging as a new frontier in photonics research. Recently, twisted moiré photonic crystal has become a competitive candidate for implementing reconfigurable optics because of its high degree of tunability. However, despite its great potential as versatile optics components, simultaneous and dynamic modulation of multiple degrees of freedom in twisted moiré photonic crystal has remained out of reach, severely limiting its area of application. In this paper, we present a MEMS-integrated twisted moiré photonic crystal sensor that offers precise control over the interlayer gap and twist angle between two photonic crystal layers, and demonstrate an active twisted moiré photonic crystal-based optical sensor that can simultaneously resolve wavelength and polarization. Leveraging twist- and gap-tuned resonance modes, we achieve high-accuracy spectropolarimetric reconstruction of light using an adaptive sensing algorithm over a broad operational bandwidth in the telecom range and full Poincaré sphere. Our research showcases the remarkable capabilities of multidimensional control over emergent degrees of freedom in reconfigurable nanophotonics platforms and establishes a scalable pathway towards creating comprehensive flat-optics devices suitable for versatile light manipulation and information processing tasks.

Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon-vacancy centers have been shown to operate at temperatures beyond 1 K without phonon-mediated decoherence. In this work, we combine high-stress silicon-nitride thin films with diamond nanostructures to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of ∼4×10−4. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5 K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well.

Metasurfaces and photonic crystals have revolutionized classical and quantum manipulation of light, and opened the door to studying various optical singularities related to phases and polarization states. However, traditional nanophotonic devices lack reconfigurability, hindering the dynamic switching and optimization of optical singularities. This paper delves into the underexplored concept of tunable bilayer photonic crystals (BPhCs), which offer rich interlayer coupling effects. Utilizing silicon nitride-based BPhCs, we demonstrate tunable bidirectional and unidirectional polarization singularities, along with spatiotemporal phase singularities. Leveraging these tunable singularities, we achieve dynamic modulation of bound-state-in-continuum states, unidirectional guided resonances, and both longitudinal and transverse orbital angular momentum. Our work paves the way for multidimensional control over polarization and phase, inspiring new directions in ultrafast optics, optoelectronics, and quantum optics.

Silicon color centers have recently emerged as promising candidates for commercial quantum technology, yet their interaction with electric fields has yet to be investigated. In this paper, we demonstrate electrical manipulation of telecom silicon color centers by fabricating lateral electrical diodes with an integrated G center ensemble in a commercial silicon on insulator wafer. The ensemble optical response is characterized under application of a reverse-biased DC electric field, observing both 100% modulation of fluorescence signal, and wavelength redshift of approximately 1.4 GHz/V above a threshold voltage. Finally, we use G center fluorescence to directly image the electric field distribution within the devices, obtaining insight into the spatial and voltage-dependent variation of the junction depletion region and the associated mediating effects on the ensemble. Strong correlation between emitter-field coupling and generated photocurrent is observed. Our demonstration enables electrical control and stabilization of semiconductor quantum emitters.

Abstract Bulk acoustic resonators can be fabricated on the same substrate as other components and can operate at various frequencies with high quality factors. Mechanical dynamic metrology of these devices is challenging as the surface information available through laser Doppler vibrometry lacks information about the acoustic energy stored in the bulk of the resonator. Here we report the spin-acoustic control of naturally occurring negatively charged silicon monovacancies in a lateral overtone bulk acoustic resonator that is based on 4H silicon carbide. We show that acoustic driving can be used at room temperature to induce coherent population oscillations. Spin-acoustic resonance is shown to be useful as a frequency-tunable probe of bulk acoustic wave resonances, highlighting the dynamical strain distribution inside a bulk acoustic wave resonator at ambient operating conditions. Our approach could be applied to the characterization of other high-quality-factor microelectromechanical systems and has the potential to be used in mechanically addressable quantum memory.

Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color-centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon vacancy centers have been shown to operate at temperatures beyond 1K without phonon-mediated decoherence. In this work we combine high-stress silicon nitride thin films with diamond nanostructures in order to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of $\sim 4 \times 10^{-4}$. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well.

We demonstrate optically pumped blue lasing at room temperature in a merged moiré photonic crystal fabricated out of gallium nitride with embedded, fragmented quantum wells. Lasing occurs at two closely spaced wavelengths of 450 and 451 nm, matched to simulated flat bands induced by the moiré superlattice. Both thresholds occur at 30 μJ/cm 2 . Light in–light out curves were taken at both room temperature and 77 K across different gain materials, including fragmented quantum wells, continuous quantum wells, and quantum dots. Lasing was observed only at room temperature in fragmented quantum well devices, suggesting the importance of gain material carrier dynamics in unconventional laser cavities like the moiré design explored. These insights and the experimental validation of moiré simulations in a previously unexplored III–V material indicate promise toward a new kind of efficient, tunable laser.

Upload of data used for figure production in "SPIN-ACOUSTIC CONTROL OF SILICON VACANCIES IN 4H SILICON<br> CARBIDE"

High-yield engineering and characterization of cavity–emitter coupling is an outstanding challenge in developing scalable quantum network nodes. Ex situ defect formation systems prevent real-time analysis, and previous in situ methods are limited to bulk substrates or require further processing to improve the emitter properties^ 1 – 6 . Here we demonstrate the direct laser writing of cavity-integrated spin defects using a nanosecond pulsed above-bandgap laser. Photonic crystal cavities in 4H-silicon carbide serve as a nanoscope monitoring silicon-monovacancy defect formation within the approximately 200 nm^3 cavity-mode volume. We observe spin resonance, cavity-integrated photoluminescence and excited-state lifetimes consistent with conventional defect formation methods, without the need for post-irradiation thermal annealing. We further find an exponential reduction in excited-state lifetime at fluences approaching the cavity amorphization threshold and show the single-shot annealing of intrinsic background defects at silicon-monovacancy formation sites. This real-time in situ method of localized defect formation, paired with cavity-integrated defect spins, is necessary towards engineering cavity–emitter coupling for quantum networking. Using direct laser writing with a nanosecond pulsed laser operating at above-bandgap photon energies, we demonstrate the selective formation of spin defects in photonic crystal cavities in 4H-silicon carbide and their in situ characterization.