Scalable quantum interference in integrated lithium niobate nanophotonics

Photonics has emerged as one of the leading platforms for the implementation of real-world-applicable quantum technologies, enabling secure communication, enhanced sensing capabilities, as well as resolving previously intractable computational challenges. However, to harness the full potential of the photonics platform, several engineering feats need to be accomplished, among those is the quest for a scalable source of pure single photons. While single photon sources can be implemented in a variety of different ways, integrated lithium niobate stands out as a prime contender for a monolithic quantum photonics platform, given its second-order nonlinearity and proven classical scalability. Despite the extensive effort put into developing the platform, integrating suitable photon pair sources remains a hurdle limiting the scalability of quantum photonic systems in lithium niobate. We engineer three-wave-mixing in a nanophotonic lithium niobate device, integrating multiple near-perfect spectrally separable heralded single photon sources. By mixing photons generated via the developed sources, we show bosonic interference between indistinguishable photons, a crucial interaction for many photonic quantum computing protocols. This demonstration of the first proof-of-principle multi-source interference in integrated lithium niobate contributes to developing a truly scalable quantum photonics platform.