A composite microcavity of diamond nanopillar and deformed silica microsphere with enhanced evanescent decay length

We report the experimental realization of a composite microcavity system, in which negatively-charged nitrogen vacancy (NV) centers in diamond nanopillars couple evanescently to whispering-gallery modes (WGMs) in a deformed, non-axisymmetric silica microsphere. We show that the deformed microsphere can feature an evanescent decay length four times larger than that of a regular silica microsphere. With the enhanced evanescent coupling, WGMs can in principle couple to NV centers that are 100 to 200 nm beneath the diamond pillar surface, providing a promising avenue for exploring evanescently-coupled cavity QED systems of NV centers in ultrahigh purity diamond.