Entangled Photon Triplets Using Lithium Niobate Nanophotonics

Abstract Multiphoton states are needed for quantum communication and computation. Multiphoton states are significantly more difficult to generate than one- and two-photon states because two individual downconversion processes must be cascaded. Only efficiencies of <100 Hz/mW have been reported to date. We integrate two downconverters on the same thin-film lithium niobate waveguide, significantly enhancing the cascaded process efficiency to 237 ± 36 kHz/mW. The measured 4.4 × 10–5 probability of the second downconverter, which sets the limit on detectable triplet rates, exceeds those of previous triplet sources by an order of magnitude and demonstrates a path toward MHz rates of triplets for quantum applications.