A device for achieving multi-photon interference is provided based on nitrogen-vacancy defects in diamond material. Nitrogen-vacancy defects having a narrow band width and a similar emission frequency are identified within a high quality diamond material. The device has an excitation arrangement configured to individually address nitrogen-vacancy defects and optical outcoupling structures for increasing outcoupling of photons from each nitrogen-vacancy defect. A tuning arrangement is configured to tune the emission from each nitrogen-vacancy defect to reduce differences in frequency and the photons are overlapped. A detector is provided to detect the photon emissions. The detector is configured to resolve sufficiently small differences in photon detection times such that tuned photon emissions from the nitrogen-vacancy defects are quantum mechanically indistinguishable resulting in quantum interference between indistinguishable photon emissions from different nitrogen-vacancy defects.