  Arrays of nonlinear resonators offer a fertile ground for a wide range of
complex phenomena and opportunities for advanced photonic sensing and
computing. Recently, significant attention has focused on studying coupled
resonators in special-purpose configurations either on chips or in table-top
experiments. However, a path to realizing a large-scale programmable network of
nonlinear photonic resonators remains elusive because of the challenges
associated with simultaneously achieving strong nonlinearity, independent
operation of the resonators, and programmability of the couplings. In this
work, we break these barriers by realizing large-scale, time-multiplexed
optical parametric oscillators (OPOs) on a single lithium niobate nanophotonic
chip. We show independent operation of 70 identical OPOs in an ultrafast
nanophotonic circuit. The OPOs exhibit an ultra-low threshold of a few
picojoules, substantially surpassing the strength of nonlinearity of other
platforms. Using our ultrafast nanophotonic circuit, a network of N OPOs with
programmable all-to-all couplings requires only a few additional components.
The time-multiplexed nanophotonic OPOs can enable myriad applications,
including ultrafast classical and quantum information processing.
