  Generating and interfering non-classical states of light is fundamental to
optical quantum information science and technology. Quantum photonic integrated
circuits provide one pathway towards scalability by combining nonlinear sources
of non-classical light and programmable circuits in centimeter-scale devices.
The key requirements for quantum applications include efficient generation of
indistinguishable photon-pairs and high-visibility programmable quantum
interference. Here, we demonstrate a lithium niobate-on-insulator (LNOI)
integrated photonic circuit that generates a two-photon path-entangled state,
and a programmable interferometer for quantum interference. We generate
entangled photons with $\sim2.3\times10^8$ pairs/s/mW brightness and perform
quantum interference experiments on the chip with $96.8\pm3.6\%$ visibility.
LNOI is an emerging photonics technology that has revolutionized high-speed
modulators and efficient frequency conversion. Our results provide a path
towards large-scale integrated quantum photonics including efficient
photon-pair generation and programmable circuits for applications such as boson
sampling and quantum communications.
