Ultrabright source of non-degenerate polarization-entangled photon pairs based on off-the-shelf polarization optics

Abstract

We report a Sagnac-type source based on a MgO:PPLN non-linear crystal pumped with a 532 nm continuous-wave laser, which generates spectrally non-degenerate, polarization-entangled photon pairs of 785 nm signal and 1651 nm idler wavelength, via the type-0 spontaneous parametric downconversion (SPDC) process. We use standard off-the-shelf components; hence, no custom-designed multi-wavelength polarization optics are required. At the same time, long-term phase stability can be achieved due to the geometry of our Sagnac-type design. The source's brightness is 6.17(4)×106 pairs/sec/mW, which is comparable to the brightest state-of-the-art non-degenerate polarization-entangled photon-pair source. The spectral bandwidth of the single photon is approximately 195 GHz (root mean square). The fidelity of the entangled state is measured to be 96.72(1)%, the concurrence is 94.7(2)%, and the Bell-CHSH value S=2.71(6). This source has the potential to be applied in long-distance quantum communication using both free-space and fiber links simultaneously.