Emission of nitrogen-vacancy centres in diamond shaped by topological photonic waveguide modes.

As the ability to integrate single-photon emitters into photonic architectures improves, so does the need to characterize and understand their interaction. Here we use a scanning diamond nanocrystal to investigate the interplay between the emission of room-temperature nitrogen-vacancy (NV) centres and a proximal topological waveguide. In our experiments, NVs serve as local, spectrally broad light sources, which we exploit to characterize the waveguide bandwidth as well as the correspondence between the light injection site and the directionality of wave propagation. We find that near-field coupling to the waveguide influences the spectral shape and ellipticity of the NV photoluminescence, revealing nanostructured light fields through polarization and amplitude contrasts exceeding 50%, with a spatial resolution set by the nanoparticle size. Our results expand on the sensing modalities afforded by colour centres, highlighting novel opportunities for on-chip quantum optics devices that leverage topological photonics to optimally manipulate and read out single-photon emitters.