With in-built advantages (high quantum efficiency and room temperature photostability<sup>1</sup>) for deployment in quantum technologies as a bright on-demand source of single photons, the nitrogen vacancy (NV) center is the most widely studied optical defect in diamond. Despite significant success in controlling its spontaneous emission<sup>2</sup>, the fundamental understanding of its photo-physics in various environments and host material remains incomplete. Studying NV photoemission from nanodiamonds on a glass substrate, we recently pointed out a disparity between the measured and calculated decay rates (assuming near unity quantum efficiency)<sup>3</sup>. This indicates the presence of some strong nonradiative influences from factors most likely intrinsic to nanodiamond itself. To obtain a clearer picture of the NV emission, here we remove the substrate contributions to the decay rates by embedding our nanodiamonds inside silica aerogel, a substrate-free environment of effective index <i>n</i> ~ 1.05.
Nanodiamond doped aerogel samples were fabricated using the “two-step” process<sup>4</sup>. Time-resolved fluorescence measurement on ~20 centers for both coverslip and aerogel configurations, showed an increase in the mean lifetime (~37%) and narrowing of the distribution width (~40%) in the aerogel environment, which we associate with the absence of a air/cover-glass interface near the radiating dipoles<sup>3</sup>. Finite difference time domain (FDTD) calculations showed the strong influence of the irregular nanodiamond geometry on the remaining distribution width. Finally a comparison between measurements and calculations provides an estimate of the quantum efficiency of the nanodiamond NV emitters as ~0.7. This value is apparently consistent with recent reports concerning the oscillation of the NV center between negative and neutral charge states<sup>5</sup>.
Nitrogen-vacancy centers in diamond typically have spin-conserving optical transitions, a feature which allows
for optical detection of the long-lived electronic spin states through fluorescence detection. However, by applying
stress to a sample it is possible to obtain spin-nonconserving transitions in which a single excited state couples to
multiple ground states. Here we describe two-frequency optical spectroscopy on single nitrogen-vacancy centers
in a high-purity diamond sample at low temperature. When stress is applied to the sample it is possible to
observe coherent population trapping with a single center. By adjusting the stress it is possible to obtain a
situation in which all of the transitions from the three ground sublevels to a common excited state are strongly
allowed. These results show that all-optical spin manipulation is possible for this system, and we propose that
that by coupling single centers to optical microcavities, a scalable quantum network could be realized for photonic
quantum information processing.
Moore's Law has set great expectations that the performance/price ratio of commercially available semiconductor
devices will continue to improve exponentially at least until the end of the next decade. Although the physics
of nanoscale silicon transistors alone would allow these expectations to be met, the physics of the metal wires
that connect these transistors will soon place stringent limits on the performance of integrated circuits. We
will describe a Si-compatible global interconnect architecture - based on chip-scale optical wavelength division
multiplexing - that could precipitate an "optical Moore's Law" and allow exponential performance gains until
the transistors themselves become the bottleneck. Based on similar fabrication techniques and technologies, we
will also present an approach to an optically-coupled quantum information processor for computation beyond
Moore's Law, encouraging the development of practical applications of quantum information technology for
commercial utilization. We present recent results demonstrating coherent population trapping in single N-V
diamond color centers as an important first step in this direction.
We describe how a quantum non-demolition device based on electromagnetically-induced transparency in solidstate atom-like systems could be realized. Such a resource, requiring only weak optical nonlinearities, could potentially enable photonic quantum information processing (QIP) that is much more efficient than QIP based on linear optics alone. As an example, we show how a parity gate could be constructed. A particularly interesting physical system for constructing devices is the nitrogen-vacancy defect in diamond, but the excited-state structure for this system is unclear in the existing literature. We include some of our latest spectroscopic results that indicate that the optical transitions are generally not spin-preserving, even at zero magnetic field, which allows the realization of a Λ-type system.