Person:

Cui, Shanying

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.

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.

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.

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.