Generation of Polarization-Entangled Photons via type-II SPDC in a Sagnac Interferometer

A polarization-entangled photon pair source has been constructed based on a Sagnac interferometer, following the design outlined in Ref. [1]. A pulsed laser at 780 nm pumps a periodically poled potassium titanyl phosphate (PPKTP) crystal, where type-II spontaneous parametric down-conversion (SPDC) generates orthogonally polarized signal and idler photon pairs. Bidirectional SPDC within the Sagnac loop allows for coherent superposition of the down-converted pairs, resulting in polarization entanglement. The photon pairs are detected using superconducting nanowire single-photon detectors (SNSPDs), which provide high detection efficiency. This source enables investigations into the spectral-temporal shaping of entangled photon pairs for applications in quantum networks [2,3].

[1] Jin, Rui-Bo, et al. “Pulsed Sagnac Polarization-Entangled Photon Source with a PPKTP Crystal at Telecom Wavelength.” Opt. Express, vol. 22, no. 10, 2014, pp. 11498–11498, https://doi.org/10.1364/oe.22.011498.

[2] Filip Sośnicki, et al. “Interface between Picosecond and Nanosecond Quantum Light Pulses.” Nat. Photonics, vol. 17, no. 9, 2023, pp. 761–766, https://doi.org/10.1038/s41566-023-01214-z.

[3] Michał Karpiński, et al. “Control and Measurement of Quantum Light Pulses for Quantum Information Science and Technology.” Adv. Quantum Technol., vol. 4, no. 9, 2021, https://doi.org/10.1002/qute.202000150.