  Photonic entangled states lie at the heart of quantum science for the
demonstrations of quantum mechanics foundations and supply as a key resource
for approaching various quantum technologies. An integrated realization of such
states will certainly guarantee a high-degree of entanglement and improve the
performance like portability, stability and miniaturization, hence becomes an
inevitable tendency towards the integrated quantum optics. Here, we report the
compact realization of steerable photonic path-entangled states from a
monolithic quadratic nonlinear photonic crystal. The crystal acts as an
inherent beam splitter to distribute photons into coherent spatial modes,
producing the heralded single-photon even appealing beamlike two-photon
path-entanglement, wherein the entanglement is characterized by quantum spatial
beatings. Such multifunctional entangled source can be further extended to
high-dimensional fashion and multi-photon level as well as involved with other
degrees of freedom, which paves a desirable way to engineer miniaturized
quantum light source.
