Fig. 1. Schematic diagram of the preparation of a heralded single photon source using entangled photons. The laser pumped nonlinear crystal causes parametric down-conversion to produce entangled signal light (s, the lower path in the figure) and idle light (i, the upper one in the figure); Detecting signal photons to “herald” the twinned photon into single photons.利用纠缠光子对制备宣布式单光子源的原理示意图　激光抽运非线性晶体使其发生参量下转换, 产生纠缠的信号光(s, 图中下面一路)和闲置光(i, 图中上面一路); 探测信号光子从而将其孪生的闲置光子“宣布”为单光子

Fig. 2. Schematic diagram of generating entangled photon pairs using class I BBO nonlinear crystals. The cone represents the light field distribution, and the intersection with the upper and lower light paths is the collection point of the photon signal, and the acquired photon polarization is or . 利用I类BBO非线性晶体产生纠缠光子对的原理简图　圆锥表示光场分布, 与上下光路的交叉点为光子信号的采集点, 所采集的光子偏振为 或者为

Fig. 3. Schematic diagram of entangled photon pair polarization correlation measurement. The polarized beam splitter (PBS) before Lens is used to filter out horizontally polarized lasers, the half-wave plate (HWP) before the BBO crystal is used to generate polarized superimposed pump light, and BBO is used to generate entangled photon pairs. A half-wave plate, a filter, a PBS, and a detector constitute a photon polarization detection system, coincidence counter records and display the coincidence signals for two single photon detectors.纠缠光子对偏振关联测量原理图　透镜(Lens)之前的极化分束器(PBS)的作用是滤掉水平偏振的激光(取其反射光进入透镜, 这里省略了反射光路), BBO晶体之前的半波片(HWP)用于产生偏振叠加抽运光, BBO用于产生纠缠双光子, 半波片、滤波片(Filter)、PBS和探测器构成光子的偏振探测系统, 符合计数器记录并显示两个单光子探测器的符合信号

Fig. 4. Experimental measurement results of the polarization correlations for entangled photon-pairs.纠缠光子偏振关联的实验测量结果

Fig. 5. Schematic diagram of the HBT experiment, wherein a laser beam is splitted, after a 50/50 beam splitter, into two paths; one of them is delayed by a duration , then the signals of the two paths are detected by the two detectors, respectively. The simultaneity of the detected signals is characterized by the coincidence countings. HBT实验原理图　一束光通过50/50分束器后被均分为两路(其中一路经过延时 ), 最后两路信号分别被两个探测器所探测, 其同时性由符合计数特性表征

Fig. 6. The measured second-order coherence for the idle light field without being heralded by the signal light.不对信号光宣布而直接测量闲置光场二阶相干度的实验结果

Fig. 7. Optical path system for measuring the heralded efficiency of the heralded single photons.宣布式单光子场的二阶关联函数实验测量光路图

Fig. 8. Measurement results of second-order coherence of the single photon field.宣布式单光子场二阶相干度测量结果