Increased negatively charged nitrogen-vacancy centers in fluorinated diamond

We investigated the effect of fluorine-terminated diamond surface on the charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is achieved with $CF_4$ plasma, and the surface chemistry is confirmed with x-ray photoemission spectroscopy. Photoluminescence of these ensemble NVs reveals that fluorine-treated surfaces lead to a higher and more stable negatively charged nitrogen vacancy $(NV^−)$ population than oxygen-terminated surfaces. $NV^−$ population is estimated by the ratio of negative to neutral charged NV zero-phonon lines. Surface chemistry control of $NV^−$ density is an important step towards improving the optical and spin properties of NVs for quantum information processing and magnetic sensing.Engineering and Applied Science

Near-surface Nitrogen Vacancy Centers in Diamond

The nitrogen-vacancy (NV) center is a point defect in diamond and has been championed as a promising solid-state "artificial atom." NV center properties such as its bright luminescence, room-temperature optical readout of spin states, and long spin decoherence lifetime make it an excellent system for applications in quantum information processing, high sensitivity magnetometry, and biotagging. In all applications, near-surface NVs are desirable. However, it has been found that the favorable properties of the NV center are significantly diminished as the NV center nears the surface. This dissertation presents efforts in understanding the effect of the surface on the luminescence of NV centers less than a wavelength of light from the surface. We use plasma assisted etching to, independently, change the surface termination and bring the NV closer to the surface. We find that treating the surface with CF4 plasma results in a deposited polymerous fluorocarbon which helps stabilize nearby NVs. We propose using a downstream etcher to bring NVs closer to the surface, while minimizing damage and maintaining NV luminescence. Finally, we enhance emission of these near-surface NVs by coupling them into a hybrid diamond plasmonic cavity. The fabricated devices result in a measured Q of 170, higher than other previously fabricated diamond plasmonic devices.Engineering and Applied Science

Controlled mode tuning in 1-D ‘RIM’ plasmonic crystal trench cavities probed with coupled optical emitters

We present a design of plasmonic cavities that consists of two sets of 1-D plasmonic crystal reflectors on a plasmonic trench waveguide. A 'reverse image mold' (RIM) technique was developed to pattern high-resolution silver trenches and to embed emitters at the cavity field maximum, and FDTD simulations were performed to analyze the frequency response of the fabricated devices. Distinct cavity modes were observed from the photoluminescence spectra of the organic dye embedded within these cavities. The cavity geometry facilitates tuning of the modes through a change in cavity dimensions. Both the design and the fabrication technique presented could be extended to making trench waveguide-based plasmonic devices and circuits.Engineering and Applied Science

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 ~ $0.47({\lambda}/n)^{3}$ 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.Comment: 13 pages, 3 figure

Large spontaneous emission enhancement in plasmonic nanocavities

Cavity–emitter coupling can enable a host of potential appli- cations in quantum optics, from low-threshold lasers to brighter single-photon sources for quantum cryptography1. Although some of the first demonstrations of spontaneous emission modification occurred in metallic structures2,3, it was only after the recent demonstration of cavity quantum electrody- namics effects in dielectric optical cavities4 that metal-based optical cavities were considered for quantum optics appli- cations5–13. Advantages of metal–optical cavities include their compatibility with a large variety of emitters and their broad- band cavity spectra, which enable enhancement of spectrally broad emitters. Here, we demonstrate radiative emission rate enhancements approaching 1,000 for emitters coupled to the nanoscale gap between a silver nanowire and a silver substrate. A quantitative comparison of our results with analytical theory shows that the enhanced emission rate of gap-mode plasmons in our structures can yield high internal quantum efficiency despite the close proximity of metal surfaces.Engineering and Applied Science

Hybrid Plasmonic Photonic Crystal Cavity for Enhancing Emission from near-Surface Nitrogen Vacancy Centers in Diamond

Optical cavities create regions of high field intensity, which can be used for selective spectral enhancement of emitters such as the nitrogen vacancy center (NV) in diamond. This report discusses a hybrid metal–diamond photonic crystal cavity, which provides greater localization of the electric field than dielectric cavities and mitigates metal-related losses in existing plasmonic structures. We fabricated such hybrid structures using silver and single-crystal diamond and observed emission enhancement of NVs near the diamond surface. We measured a mode quality factor (<i>Q</i>) as high as 170 with a simulated mode volume of ∼0.1 (λ/<i>n</i>)³ and demonstrated its tunability. This cavity design and the associated fabrication approach specifically target enhancement of emission from near-surface NVs