基于PPLN波导非线性效应的确定性量子纠缠网络实验研究

量子纠缠网络是应用量子信息和检验量子理论的重要平台。纠缠交换是构建量子纠缠网络的关键技术。然而，基于线性光学纠缠交换的量子纠缠网络在没有后选择的情况下无法使用。为此亟需研制出确定性的量子纠缠网络。我们预研发现，基于非线性光学技术理论上可以实现无需后选择的纠缠交换，这为构建确定性的量子纠缠网络提供了重要途径。我们前期研究已实现单光子源和单光子的非线性作用。本项目基于周期性极化铌酸锂（PPLN）波导良好的非线性特性，围绕“确定性量子纠缠网络”的主题，拟开展以下研究：（1）高亮度单光子源的非线性产生；（2）远距离的量子纠缠分发；（3）确定性的量子纠缠交换；（4）基于纠缠交换的量子安全直接通信。通过4年的努力，实现一个确定性的量子纠缠网络，完成300公里以上的纠缠分发，实现各用户间共享纠缠态的保真度均大于90%，完成点对点的量子安全直接通信，为构建大规模地面量子纠缠网络提供理论依据和实验基础。

Quantum entanglement network is an important platform for applying quantum information and testing quantum theory. Entanglement swapping is the key technology for constructing quantum entanglement networks. However, quantum entanglement networks based on linear optical entanglement swapping cannot be used without post-selection. Therefore, it is urgent to develop a deterministic quantum entanglement network. Our preliminary research found that based on nonlinear optical technology, quantum entanglement swapping without post-selection can be realized in theory, which provides an important way to build a deterministic quantum entanglement network. Our previous research has achieved a single-photon source, and nonlinear interaction between single photons. This project is going to focus on the nonlinear effect of PPLN waveguides and experimental research on quantum entanglement network, which includes the following parts: (1) Non-linear generation of high-brightness single-photon source; (2) Long-distance quantum entanglement distribution; (3) Deterministic quantum entanglement swapping; (4) Quantum secure direct communication based on entanglement swapping. After 4 years of efforts, a deterministic quantum entanglement network has been implemented, entanglement distribution over 300 kilometers has been completed, the fidelity of any two users sharing entanglement states is greater than 90%, and point-to-point quantum secure direct communication has been realized. This project will provide theoretical and experimental basis for building a large-scale ground entanglement swapping quantum communication network.