arXiv subjects

Evelyn L. Hu

Publications and source records attributed to Evelyn L. Hu.

At least 19 recordsLinked to original sources

arXiv2026

Hysteresis and trap emission in dc-biased integrated lithium niobate electro-optic modulators

The electro-optic effect is crucially important for low power and efficient tuning of integrated photonic circuits. However, in electro-optic materials such as lithium niobate, dc biasing for an extended duration of time results in the emergence of numerous nonidealities, including hysteresis -- a persistent degradation of the magnitude and linearity of the dc electro-optic response. We show that electro-optic hysteresis can be reversed under both zero-bias and reverse-bias conditions, given sufficient time or reverse voltage and consistent with a defect model of the underlying physics. Specifically, we find that drift phenomena at short time scales can be explained by charge trapping dynamics near the contact junction, and thereby devise an active reset protocol that restores the magnitude of the response and partially restores the drift time scales.

physics.optics↗

arXiv2026

Resolving and resetting the charge environment of single T-centers in silicon p-i-n waveguides

The silicon T-center is a telecom-band spin-photon interface in a manufacturable photonics platform. In nanophotonic devices, however, its optical linewidth is broadened by a fluctuating charge environment, limiting photon indistinguishability for quantum networking. Here, we address this challenge through characterization and suppression of the local charge-noise of single T-centers in lateral p-i-n waveguides, demonstrating an unheralded method of T-center optical linewidth narrowing. Above-band illumination resets the charge environment, neutralizing the local field and suppressing spectral diffusion. Across 46 emitters this reset narrows the median linewidth 3.5-fold to 0.57(11) GHz, and an optimized emitter reaches 128(22) MHz, the narrowest unheralded linewidth reported for an integrated T-center. The narrowed transition supports coherent optical Rabi oscillations with a coherence time of 20(2) ns. Finally, we perform Stark-shift tuning using the p-i-n junction, and read out the local electric field and the charge-noise width at 15 mK. An analytical model of proximal surfaces, bulk, and junction field effects provides good agreement with our findings. Our multi-pronged characterization of the nanophotonic-integrated T-center charge environment enables future device optimization toward scalable quantum interconnects.

quant-ph↗

arXiv2026

Probing negative differential resistance in silicon with a P-I-N diode-integrated T center ensemble

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.

quant-ph↗

arXiv2025

A Suspended 4H-Silicon Carbide Membrane Platform for Defect Integration into Quantum Devices

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, 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.

physics.app-ph↗

arXiv2024

Selective Undercut of Undoped Optical Membranes for Spin-Active Color Centers in 4H-SiC

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.

physics.app-ph↗

arXiv2023

Three Dimensional Reconfigurable Optical Singularities in Bilayer Photonic Crystals

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.

physics.optics↗

arXiv2023

Electrical Manipulation of Telecom Color Centers in Silicon

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.

quant-ph↗

arXiv2022

Deterministic Laser Writing of Spin Defects in Nanophotonic Cavities

High-yield engineering and characterization of cavity-emitter coupling is an outstanding challenge in developing scalable quantum network nodes. Ex-situ defect formation processes prevent real-time defect-cavity characterization, and previous in-situ methods require further processing to improve emitter properties or are limited to bulk substrates. We demonstrate 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 (V$_{Si}^-$) defect formation within the $100~\text{nm}^3$ cavity mode volume. We observe defect spin resonance, cavity-integrated photoluminescence and excited-state lifetimes consistent with conventional defect formation methods, without 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 single-shot local annealing of the intrinsic background defects at the V$_{Si}^-$ formation sites. This real-time in-situ method of localized defect formation, paired with demonstration of cavity-integrated defect spins, marks an important step in engineering cavity-emitter coupling for quantum networking.

physics.app-ph↗

arXiv2022

Spin-Acoustic Control of Silicon Vacancies in 4H Silicon Carbide

We demonstrate direct, acoustically mediated spin control of naturally occurring negatively charged silicon monovacancies (V$_{Si}^-$) in a high quality factor Lateral Overtone Bulk Acoustic Resonator fabricated out of high purity semi-insulating 4H-Silicon Carbide. We compare the frequency response of silicon monovacancies to a radio-frequency magnetic drive via optically-detected magnetic resonance and the resonator's own radio-frequency acoustic drive via optically-detected spin acoustic resonance and observe a narrowing of the spin transition to nearly the linewidth of the driving acoustic resonance. We show that acoustic driving can be used at room temperature to induce coherent population oscillations. Spin acoustic resonance is then leveraged to perform stress metrology of the lateral overtone bulk acoustic resonator, showing for the first time the stress distribution inside a bulk acoustic wave resonator. Our work can be applied to the characterization of high quality-factor micro-electro-mechanical systems and has the potential to be extended to a mechanically addressable quantum memory.

physics.app-ph↗

arXiv2022

Optical and Strain Stabilization of Point Defects in Silicon Carbide

The photoluminescence and spin properties of ensembles of color centers in silicon carbide are enhanced by fabricating optically isolated slab waveguide structures and carefully controlling annealing and cooling conditions. We find that the photoluminescence signal of an ensemble of implanted defects is enhanced in slab waveguides by an order of magnitude over identically implanted bulk defects. The slab waveguide-enhanced photoluminescence of several defect species is used to study recombination and diffusion in the presence of thermal annealing with both rapid quench cooling and a longer return to ambient conditions. The confined mechanical geometry of the thin film is exploited to measure the spin-strain coupling of the negatively charged silicon monovacancy. The methods in this work can be used to exercise greater control on near-surface emitters in silicon carbide and better understand and control the effects of strain on spin measurements of silicon carbide based color centers.

cond-mat.mtrl-sci↗

arXiv2020

Enhanced cavity coupling to silicon monovacancies in 4-H Silicon Carbide using below bandgap laser irradiation and low temperature thermal annealing

The negatively charged silicon monovacancy $V_{Si}^-$ in 4H-silicon carbide (SiC) is a spin-active point defect that has the potential to act as a qubit or quantum memory in solid-state quantum computation applications. Photonic crystal cavities (PCCs) can augment the optical emission of the $V_{Si}^-$, yet fine-tuning the defect-cavity interaction remains challenging. We report on two post-fabrication processes that result in enhancement of the $V_1^{'}$ optical emission from our 1-dimensional PCCs, indicating improved coupling between the ensemble of silicon vacancies and the PCC. One process involves below bandgap illumination at 785 nm and 532 nm wavelengths and above bandgap illumination at 325 nm, carried out at times ranging from a few minutes to several hours. The other process is thermal annealing at $100^o C$, carried out over 20 minutes. Every process except above bandgap irradiation improves the defect-cavity coupling, manifested in augmented Purcell factor enhancement of the $V_1^{'}$ zero phonon line at 77K. The below bandgap laser process is attributed to a modification of charge states, changing the relative ratio of $V_{Si}^0$ (dark state) to $V_{Si}^-$ (bright state), while the thermal annealing process may be explained by diffusion of carbon interstitials, $C_i$, that subsequently recombine with other defects to create additional $V_{Si}^-$s. Above bandgap radiation is proposed to initially convert $V_{Si}^{0}$ to $V_{Si}^-$, but also may lead to diffusion of $V_{Si}^-$ away from the probe area, resulting in an irreversible reduction of the optical signal. Observations of the PCC spectra allow insights into defect modifications and interactions within a controlled, designated volume and indicate pathways to improve defect-cavity interactions.

physics.optics↗

arXiv2016

Selective Purcell enhancement of two closely linked zero-phonon transitions of a silicon carbide color center

Point defects in silicon carbide are rapidly becoming a platform of great interest for single photon generation, quantum sensing, and quantum information science. Photonic crystal cavities (PCC) can serve as an efficient light-matter interface both to augment the defect emission and to aid in studying the defects' properties. In this work, we fabricate 1D nanobeam PCCs in 4H-silicon carbide with embedded silicon vacancy centers. These cavities are used to achieve Purcell enhancement of two closely spaced defect zero-phonon lines (ZPL). Enhancements of >80-fold are measured using multiple techniques. Additionally, the nature of the cavity coupling to the different ZPLs is examined.

cond-mat.mes-hall↗

arXiv2014

Deterministic coupling of delta-doped NV centers to a nanobeam photonic crystal cavity

The negatively-charged nitrogen vacancy center (NV) in diamond has generated significant interest as a platform for quantum information processing and sensing in the solid state. For most applications, high quality optical cavities are required to enhance the NV zero-phonon line (ZPL) emission. An outstanding challenge in maximizing the degree of NV-cavity coupling is the deterministic placement of NVs within the cavity. Here, we report photonic crystal nanobeam cavities coupled to NVs incorporated by a delta-doping technique that allows nanometer-scale vertical positioning of the emitters. We demonstrate cavities with Q up to ~24,000 and mode volume V ~ $0.47(λ/n)^{3}$ as well as resonant enhancement of the ZPL of an NV ensemble with Purcell factor of ~20. Our fabrication technique provides a first step towards deterministic NV-cavity coupling using spatial control of the emitters.

cond-mat.mes-hall↗

arXiv2014

Distinctive Signature of Indium Gallium Nitride Quantum Dot Lasing in Microdisks Cavities

Low threshold lasers realized within compact, high quality optical cavities enable a variety of nanophotonics applications. Gallium nitride (GaN) materials containing indium gallium nitride (InGaN) quantum dots and quantum wells offer an outstanding platform to study light matter interactions and realize practical devices such as efficient light emitting diodes and nanolasers. Despite progress in the growth and characterization of InGaN quantum dots, their advantages as the gain medium in low threshold lasers have not been clearly demonstrated. This work seeks to better understand the reasons for these limitations by focusing on the simpler, limited-mode microdisk cavities, and by carrying out comparisons of lasing dynamics in those cavities using varying gain media including InGaN quantum wells, fragmented quantum wells, and a combination of fragmented quantum wells with quantum dots. For each gain medium, we utilize the distinctive, high quality (Q~5500) modes of the cavities, and the change in the highest intensity mode as a function of pump power to better understand the dominant radiative processes. The variations of threshold power and lasing wavelength as a function of gain medium help us identify the possible limitations to lower-threshold lasing with quantum dot active medium. In addition, we have identified a distinctive lasing signature for quantum dot materials, which consistently lase at wavelengths shorter than the peak of the room temperature gain emission. These findings not only provide better understanding of lasing in nitride-based quantum dot cavity systems, but also shed insight into the more fundamental issues of light matter coupling in such systems.

physics.optics↗

arXiv2013

Silicon-Vacancy Color Centers in Nanodiamonds: Cathodoluminescence Imaging Marker in the Near Infrared

We demonstrate that nanodiamonds fabricated to incorporate silicon-vacancy (Si-V) color centers provide bright, spectrally narrow, and stable cathodoluminescence (CL) in the near-infrared. Si-V color centers containing nanodiamonds are promising as non-bleaching optical markers for correlated CL and secondary electron microscopy, including applications to nanoscale bioimaging.

cond-mat.mtrl-sci↗

arXiv2013

Bottom-up Engineering of Diamond Nanostructures

Engineering nanostructures from the bottom up enables the creation of carefully engineered complex structures that are not accessible via top down fabrication techniques, in particular, complex periodic structures for applications in photonics and sensing. In this work, we propose and demonstrate a bottom up approach that can be adopted and utilized to controllably build diamond nanostructures. A realization of periodic structures and optical wave-guiding is achieved by growing nanoscale single crystal diamond through a defined pattern.

cond-mat.mtrl-sci↗

arXiv2013

Effect of fluorinated diamond surface on charge state of nitrogen-vacancy centers

We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with CF4 plasma and the surface chemistry is confirmed with x-ray photoemission spectroscopy. Photoluminescence of these ensemble NVs reveal that fluorine-treated surfaces lead to a higher negatively charged nitrogen vacancy (NV-) population than oxygen-terminated surfaces. Using surface chemistry to control NV charges, in particular increasing the density of NV- centers, is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.

cond-mat.mtrl-sci↗

arXiv2013

Photoluminescent SiC tetrapods

Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors which allow control over their geometry via simple chemical processes. Here, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow linewidth photoluminescence at wavelengths spanning the visible to near infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This new, previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics and optoelectronics.

cond-mat.mtrl-sci↗