Abstract:

Single-photon sources are crucial for fields such as optical quantum informa-tion processing and secure communication. Current heralded single-photon sources based onspontaneous parametric down-conversion in nonlinear crystals often struggle to simultaneouslyachieve high heralding efficiency and high purity, which directly limits the secure key rateand transmission distance of quantum key distribution. In this paper, we develop a high-purity, high-heralding-efficiency single-photon source based on a PPKTP nonlinear crystal using continuous-wave pumped spontaneous parametric down-conversion. By employing a longcrystal and optimizing the pump beam waist, the photon heralding efficiency and collectionefficiency are significantly improved. Under an experimental condition with a pump powerof 1 mW, source brightness of 6.3 x 10⁴ pairs/(s-mW) and heralding efficiency of 57.3%, asingle-photon purity of 0.994 6 is achieved. Additionally, the source exhibits good stability andstrong suppression of multiphoton noise. The results provide a feasible solution for fabricatinglow-cost, high-quality heralded single-photon sources.

Key words: single-photon source, PPKTP crystal, spontaneous parametric down-conversion, conditional second-order correlation function