Figure 1. Integrated tunable N00N state generator.

A ps-laser at 712 nm is coupled to an integrated directional coupler (block I on the left) to simultaneously pump two PPLN/ws (block II in the center). Each produces pairs of photons at 1310/1560 nm by SPDC. Each pair is then coupled to the state-engineering chip (block III on the right) and are deterministically separated by means of integrated WDMs. The two 1310 nm photons herald the complementary 1560 nm photons routed towards a Mach-Zehnder interferometer (MZI), which can be phase-controlled using a thermo-optic, voltage-driven, transducer placed over one of its two arms. Detection scheme: the photons are collected using single mode optical fibers. A filtering stage selects a single temporal mode per pulse. Finally, quantum correlations are measured by recording 4-fold coincidences using two detectors at the two output modes of the MZI, triggered by the detection of two heralding photons in the external modes. Filtering stage: fiber Bragg gratings (FBG) filters, wavelength-division multiplexers (WDM), Detection system: avalanche photodiodes (APD), time-to-digital converter (TDC), DC: 50/50 coupler, V: voltage controller, δt: laser pulse duration, F: laser repetition frequency.