Hong–Ou–Mandel interference in colloidal CsPbBr3 perovskite nanocrystals

In the search for novel, robust quantum emitters, inorganic lead halide perovskite nanocrystals have emerged as potential colloidal sources of coherent single photons. While colloidal perovskite nanocrystals offer a great source of synthetically scalable, tunable photon sources, observation of two-photon quantum interference from the emission of any colloidal nanoparticle has not been previously reported. In this work we prepare large CsPbBr3 nanocrystals and observe direct evidence of interference between indistinguishable single photons sequentially emitted from a single nanocrystal. We measure Hong–Ou–Mandel interference from photons in CsPbBr3 nanocrystals, showing corrected visibilities of up to 0.56 ± 0.12 in the absence of any radiative enhancement or photonic architecture. These results demonstrate the unique potential of perovskite nanocrystals to serve as scalable, colloidal sources of indistinguishable single photons. Large perovskite nanocrystals are synthesized to increase the cryogenic exciton radiative rate. At liquid helium temperatures, single photons from perovskite nanocrystals coalesce at a beam splitter, signalling the existence of indistinguishable photon emission.