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Key challenges for high-Q photonic circuits in diamond

This presentation will describe several recent results relevant to photonic networks incorporating NV centers. The first experiment relates to the intrinsic properties of NV centers in bulk diamond. An important question is what temperatures are required to emit indistinguishable photons that carry information about the electron spin state of the NV center. While the long-lived coherence in the ground-state spin sublevels persists up to room temperature, transform-limited optical transitions have been observed only at liquid-helium temperatures due to decoherence within the excited states. Recent experiments have shown that this line broadening is due in large part to population relaxation between the two orbital branches which occurs through a two-phonon process. It is difficult to conceive of an entanglement formation scheme that is insensitive to this process, and it appears most likely that a quantum-optical network based on NV centers will have to operate at liquid helium temperatures. This presentation will also summarize our latest results on coupling NV centers to optical cavities, including, for example, hybrid GaP/diamond microdisk cavities with mode volumes of a few cubic wavelengths and experimental quality factors above 25000.