High-performance source of indistinguishable polarization-entangled photons with a local oscillator reference for quantum networking

Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact, source of indistinguishable pairs of polarization entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves $(99.11\pm 0.01)\mathrm{\%}$ polarization entanglement visibility, $(96.3\pm 0.6)\mathrm{\%}$ successive-photon Hong-Ou-Mandel interference visibility, $(68.0\pm 0.1$) % heralded efficiency as detected, and $(88.6\pm 0.2)\mathrm{\%}$ interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.