  Large-photon-number quantum state is a fundamental but non-resolved request
for practical quantum information applications. Here we propose an N-photon
state generation scheme that is feasible and scalable, using lithium niobate on
insulator circuits. Such scheme is based on the integration of a common
building block called photon-number doubling unit (PDU), for deterministic
single-photon parametric down-conversion and up-conversion. The PDU relies on
10^7-optical-quality-factor resonator and mW-level on-chip power, which is
within the current fabrication and experiment limits. N-photon state generation
schemes, with cluster and GHZ state as examples, are shown for different
quantum tasks.
