  Lithium-Niobate-On-Insulator (LNOI) is emerging as a promising platform for
integrated quantum photonic technologies because of its high second-order
nonlinearity and compact waveguide footprint. Importantly, LNOI allows for
creating electro-optically reconfigurable circuits, which can be efficiently
operated at cryogenic temperature. Their integration with superconducting
nanowire single-photon detectors (SNSPDs) paves the way for realizing scalable
photonic devices for active manipulation and detection of quantum states of
light. Here we report the first demonstration of these two key components
integrated in a low loss (0.2 dB/cm) LNOI waveguide network. As an experimental
showcase of our technology, we demonstrate the combined operation of an
electrically tunable Mach-Zehnder interferometer and two waveguide-integrated
SNSPDs at its outputs. We show static reconfigurability of our system with a
bias-drift-free operation over a time of 12 hours, as well as high-speed
modulation at a frequency up to 1 GHz. Our results provide blueprints for
implementing complex quantum photonic devices on the LNOI platform.
