Generation of Entangled Photon Pairs from a Silicon Bichromatic Photonic Crystal Cavity

Integrated quantum photonics leverages the on-chip generation of nonclassical states of light to realize key function-alities of quantum devices. Typically, the generation of such nonclassical states relies on whispering gallery moderesonators, such as integrated optical micro-rings, which enhance the efficiency of the underlying spontaneous non-linear processes. While this kind of resonators excel in maximizing either the temporal confinement or the spatialoverlap between different resonant modes, they are usually associated with large mode volumes, imposing an intrin-sic limitation on the device efficiency and footprint. Here, we engineer a source of time-energy entangled photonpairs based on a silicon photonic crystal cavity, implemented in a fully CMOS-compatible platform. In this device,resonantly enhanced spontaneous four-wave mixing converts pump photon pairs into signal/idler photon pairs at theenergy-conserving condition in the telecommunication C-band. The design of the resonator is based on an effectivebichromatic confinement potential, allowing to achieve up to 9 close-to-equally spaced modes in frequency, while pre-serving small mode volumes, and the whole chip, including grating couplers and access waveguides, is fabricated ina single run on a silicon-on-insulator platform. Besides demonstrating efficient photon pair generation, we also im-plement a Franson-type interference experiment, demonstrating entanglement between signal and idler photons witha Bell inequality violation exceeding 5 standard deviations. The high generation efficiency combined with the smalldevice footprint in a CMOS-compatible integrated structure opens a pathway towards the implementation of compactquantum light sources in all-silicon photonic platforms.