Heralded Single Photon Source Based On Parametric Down-Conversion Process

Single photon is the basic precondition for realizing optical quantum information processing.Therefore,single photon source is a research hotspot in the field of quantum information in recent years.An ideal single photon source is a physical system,which emits only one photon at any time,and thus its preparation is very difficult.As a possible alternative approach,i.e.,by measuring one photon of the entangled photon pair produced by the nonlinear material parametric down-conversion process to herald another photon as the single-photon,is considered to be an effective method to realize the single photon preparation.The heralded single-photon possesses certain advantages,such as working at the room temperature,easy to be collected,and also its frequency is adjustable.However,one of the bottlenecks of this approach is that the heralded efficiency needs to be improved.Based on the physical properties of single photon wave packets,especially Gaussian single photon wave packets,we analyze the two-photon characteristics in parametric down-conversion are analyzed.A possible way to improve the heralded efficiency of the heralded single photon is then given.Furthermore,based on the experimental measurements of the second-order correlation function of the light field in the famous Hanbury Brown-Twiss(HBT)experiment,the experimental and unannounced single-photon second-order correlation functions were experimentally measured.Next,with the polarization entangled photon pair generated in the parametric down-conversion process of the class-I phase-matched nonlinear crystal barium metaborate(BBO)?we discuss how to optimize the measurement base to improve the single-photon heralded efficiency.Experimentally,we built an extended HBT experimental system using three single-photon detectors to measure heralded efficiency of the heralded single photons.The experimental results show that the second-order coherence of the heralded single-photon field satisfies the"anti-bunching" characteristic of g2(0)<1;By choosing the appropriate measurement base,the two-photon entanglement can be increased by approximately 8%,resulting in an increase of the heralded efficiency of approximately 4%.Our work suggests that higher heralded efficiency is possible by further optimizing the measurement base.