Research On Design Of Pure-State Three-Photon Source And Broadband Single-Photon Frequency Conversion

With the development of quantum information,the technologies of quantum communication and storage are becoming more and more mature.The nonclassical and nonlocal properties of photon states make it the core of quantum information processing.Light source and interface device are critical for quantum research,and wavelength conversion based on nonlinear process provides reliable support for quantum technology research.Nonlinear interaction between single photons is an indispensable part of the development of modern quantum networks.It has great prospects in many application fields,such as quantum cryptography,quantum teleportation,and quantum entanglement exchange.Among the numerous nonlinear crystals,lithium niobite has relatively higher nonlinear coefficient,which leads to a greater conversion efficiency.There is a wide range of transparency which is from 420 nm to 5200 nm.Due to the development of the process,the Li Nb O₃ crystal has good integration.The development of the waveguide chip also greatly improves the efficiency of frequency conversion.Based on the good nonlinear characteristics of PPLN,the following two aspects of work are carried out in this paper:1.Based on the cascade PPLN crystal,the pure-state photon triplet is realized theoretically in the communication band,which provides a theoretical basis for the subsequent applications of the relative quantum light sources.Due to the limitation of the refractive index of materials,the study of pure-state three-photon only be realized in?3000nm.We use Gaussian filters in part,and the crystal length and the pulse duration of the pump can be obtained through the theoretical calculation.Eventually we achieve the photonic triplet with a spectral purity of 100%in the communication band.2.High efficiency single photon sum frequency generation based on chirp technology.Most of the previous work are carried out by weak coherent light.The single photons in our experiment all come from SPDC in PPLN waveguide.By adding fiber Bragg gratings to the photons of two channels and introducing positive and negative group velocity dispersion,single photons can be more effectively applied to the sum frequency process.The efficiency of broadband single photons sum frequency can reach 10^-8.