Pulsed Sagnac polarization-entangled photon source with a PPKTP crystal at telecom wavelength

Abstract

We demonstrate pulsed polarization-entangled photons generated from a periodically poled KTiOPO 4 (PPKTP) crystal in a Sagnac interferometer configuration at telecom wavelength. Since the group-velocity-matching (GVM) condition is satisfied, the intrinsic spectral purity of the photons is much higher than in the previous scheme at around 800 nm wavelength. The combination of a Sagnac interferometer and the GVM-PPKTP crystal makes our entangled source compact, stable, highly entangled, spectrally pure and ultra-bright. The photons were detected by two superconducting nanowire single photon detectors (SNSPDs) with detection efficiencies of 70% and 68% at dark counts of less than 1 kcps. We achieved fidelities of 0.981 ± 0.0002 for |ψ − and 0.980 ± 0.001 for |ψ + respectively. This GVM-PPKTP-Sagnac scheme is directly applicable to quantum communication experiments at telecom wavelength, especially in free space.

Efficient detection of an ultra-bright single-photon source using superconducting nanowire single-photon detectors

“…From the perspective of single-photon sources, the one based on a spontaneous parametric down-conversion (SPDC) process from a periodically poled KTiOPO 4 (PPKTP) crystal has been proved to be very promising in many experiments [12][13][14][15][16][17][18][19][20][21][22][23]. The PPKTP crystal has a high nonlinear efficiency and a high damage threshold.…”