Three megahertz photon collection rate from an NV center with millisecond spin coherence

Efficient collection of the broadband fluorescence of the diamond nitrogen vacancy center is essential for a range of applications in sensing, on-demand single photon generation, and quantum information processing. Here, we introduce a circular `bullseye' diamond grating enabling a collected photon rate of $(3.0\pm0.1)\times10^6$ counts per second from a single nitrogen-vacancy center with a spin coherence time of 1.7$\pm$0.1 ms. Back-focal-plane studies indicate efficient redistribution into low-NA modes.