Efficient single-spatial-mode periodically-poled KTiOPO_4 waveguide source for high-dimensional entanglement-based quantum key distribution

摘要

We demonstrate generation of high-purity photon pairs at 1560 nm in a singlespatial mode from a periodically-poled KTiOPO_4 (PPKTP) waveguide. With nearlylossless spectral filtering, the PPKTP waveguide source shows approximately 80% single-mode fiber coupling efficiency and is well suited for high-dimensionaltime-energy entanglement-based quantum key distribution. Using high-count-rateself-differencing InGaAs single-photon avalanche photodiodes configured witheither square or sinusoidal gating, we achieve > 1 Mbit/s raw key generationwith 3 bits-per-photon encoding, and, to the best of our knowledge, the highestreported Franson quantum-interference visibility of 98.2 % without subtractionof accidental coincidences.