Sub-GHz linewidths ensembles of SiV centers in a diamond nano-pyramid revealed by charge state conversion

Producing nano-structures with embedded bright ensembles of lifetime-limited emitters is a challenge with potential high impact in a broad range of physical sciences. In this work, we demonstrate controlled charge transfer to and from dark states exhibiting very long lifetimes in high density ensembles of SiV centers hosted in a CVD-grown diamond nano-pyramid. Further, using a combination of resonant photoluminescence excitation and a frequency-selective persistent hole burning technique that exploits such charge state transfer, we could demonstrate close to lifetime-limited linewidths from the SiV centers. Such a nanostructure with thousands of bright narrow linewidth emitters in a volume much below $\lambda^3$ will be useful for coherent light-matter coupling, for biological sensing, and nanoscale thermometry.