基于非线性干涉仪的高效率可调谐纯态单光子源

Single photons with pure quantum state is a crucial resource in quantum information processing. Heralded single photon source, which is based on the quantum correlated photon pairs from spontaneous parametric process in nonlinear medium, has been recognized as a simple and effective way for generating single photons. The realization of pure-state heralded single photons requires photon pairs with a factorable joint spectrum. To fulfill this requirement, one solution is applying narrow bandpass filters to the photon pairs, but the efficiency of the source would decrease accordingly; another solution is directly controlling the spectrum of photon pairs by modifying the dispersion of the nonlinear medium, so that the loss of efficiency could be avoid. However, in current heralded single photon sources usually only one single piece of nonlinear medium is employed, so that the phase matching of parametric process and the spectral control interwind with each other and this situation limits the output flexibility of spectral control. Here we propose a new method to realize the spectral control of photon pairs by using nonlinear interferometers. In nonlinear interferometers, two- or multi-stage nonlinear media are employed, and the spectral control is realized by the quantum interference. The arrangement can significantly improve the flexibility of spectral control. This project, which focuses on the research of heralded single photon sources based on nonlinear interferometer, will not only demonstrate a new kind of high-efficiency and tunable source of pure-state single photons, but also provide a new solution for the generation and control of quantum states from parametric processes.

纯态单光子是量子信息处理中的重要资源。宣布式单光子源基于非线性介质中自发参量过程所产生的关联光子对，是一种简单有效的单光子制备途径。为了获得纯态宣布式单光子，关联光子对的联合频谱需满足可分解条件。此条件的实现途径之一是对光子对进行窄带滤波，但光源效率也会随之下降；之二是通过改变非线性介质的色散等参数，直接调控光子对频谱使其满足可分解条件，从而避免效率损失。然而，现有的宣布式单光子源多基于单级非线性介质，参量过程的相位匹配条件和光子对频谱调控相互影响，限制了调控的灵活性。本项目由此提出一种利用非线性干涉仪调控关联光子对频谱的新方法，其包含两级或多级非线性介质，利用量子干涉效应实现频谱调控，从而可显著提高调控的灵活性。本项目将围绕基于非线性干涉仪的宣布式单光子源开展研究；研究成果将不仅为量子信息处理提供一种高效率可调谐的纯态单光子源，也为基于参量过程的量子态产生和调控提供一种新的解决思路。

非线性介质中的参量过程是制备宣布式单光子源、纠缠光子源等量子光源的有效途径。当采用脉冲激光泵浦参量过程时，量子光源输出的光场通常具有一定的频谱特征，该特征关系到量子光源的量子态纯度、收集效率等关键参数。调控量子光源频谱的常规方法是设计和使用具有特定色散的非线性介质，然而这种方法调控能力较为有限，且限制了量子光源的灵活性。本项目针对上述问题，提出了基于非线性干涉仪的量子光源频谱调控新方法，并围绕该方法开展了一系列理论和实验研究。理论方面，建立了两级、多级等长、多级不等长等不同结构的非线性干涉仪理论模型；研究了非线性干涉仪输出量子关联光子对的频谱特性以及不同参数对频谱特性的影响；展示了非线性干涉仪在关联光子对频谱调控方面的作用和优势。实验方面，利用光纤系统高耦合效率的优势，演示了基于两级和多级光纤非线性干涉仪的量子关联光子对源和宣布式单光子源，实验结果表明利用非线性干涉仪结构可实现关联光子对频谱的灵活调控，从而可使量子光源同时具高量子态纯度、高收集效率以及输出波长可调的特征。项目共发表SCI期刊论文7篇、EI期刊论文1篇、会议论文5篇；获授权中国发明专利1项、美国专利1项；培养毕业硕士生4人、博士生2人。本项目的相关原理和技术还可移植到集成硅基波导等其它平台，从而为高质量实用化量子光源的制备开辟了一条有效途径。