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 down-conversion processes must be cascaded. Only efficiencies of <100 Hz/mW have been reported to date. We integrate two down-converters 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 down-converter, which sets the limit on detectable triplet rates, exceeds those of previous triplet sources by an order of magnitude and demonstrates a path towards MHz rates of triplets for quantum applications.
@article{arxiv.2512.24053,
title = {Entangled photon triplets using lithium niobate nanophotonics},
author = {Nathan A. Harper and Ayantika Sengupta and Emily Y. Hwang and Scott K. Cushing},
journal= {arXiv preprint arXiv:2512.24053},
year = {2026}
}