基于多个冷原子系综的量子网络研究

Combing the transmission with single-photons and the storage with quantum memories is a significant approach for scalable quantum networks. In recent years, significant progresses have been made in the field of experimental realization of quantum memories. So far, many physical systems have been experimentally demonstrated to have the ability to store single quantum states. Along with the continuous development of quantum memory, a lot of significant progresses have also been made in the research direction of scalable quantum networks. So far, experimental capabilities for many physical systems have now been developed to the level of manipulating two memory nodes, such as building entanglement or transmitting a single qubit between two nodes. Nevertheless, to the best knowledge of us, none of all the physical systems has shown the capability of realizing a quantum network with more than 3 separated nodes. In this proposal, we will study the main limiting factors for the further development of quantum networks very carefully, and develop further the quantum memory technique with cold atomic ensembles. We will work hard on generating high-quality atom-photon entanglement and utilizing it to study multi-node quantum networks experimentally. By making this research, we hope that we can make a significant step forward in making the jump to a quantum network with three nodes or more. This research will have important applications for future large-scale quantum networks and distributed quantum computing etc.

将单光子传输与量子存储相结合是实现可升级量子网络的重要途径之一。近年来量子存储实验研究方面发展非常迅速，到目前为止众多物理体系都已被实验证实可用于存储单量子态。伴随着量子存储研究的不断发展，可升级量子网络研究方面也有了初步发展，近年来多个物理体系中都已实现两个分立量子存储节点的操纵，如建立两节点间量子纠缠、在两节点间传输单量子比特等。但是，到目前为止还没有哪一个物理系统能够实现三节点及以上的量子网络。本课题将仔细分析当前条件下限制量子网络进一步发展的各种因素，并采用冷原子系综这一体系深入开展实验研究，发展高品质的单光子与原子系综间的量子纠缠，并应用于多节点的量子网络研究。通过本项目的顺利开展，我们拟实现量子网络首次从两节点至三节点的跨越，并以此进一步推动量子存储在量子网络中的广泛应用。该项研究对于未来全量子网络、分布式量子计算等的实现有着重要意义。

将单光子传输与量子存储相结合是实现可升级量子网络的重要途径之一。近年来量子存储实验研究方面发展非常迅速，到目前为止众多物理体系都已被实验证实可用于存储单量子态。伴随着量子存储研究的不断发展，可升级量子网络研究方面也有了初步发展，主要发展趋势是增加节点数目与拓展节点间的距离。本项目针对冷原子系综这一物理体系进行了深入研究，提升了冷原子量子存储的主要性能指标，制备了具有高读出效率的光与原子纠缠，并利用多对纠缠实现了三节点量子存储网络。在量子存储性能提升方面，我们对系综量子存储器内的单量子态的退相干机制进行了深入研究，发展了基于拉曼光的集体态操纵技术，成功地实现了系综内单量子态的自旋回波；我们还采用三维光晶格囚禁原子与环形腔增强相结合，并对光晶格导致的差分光频移效应进行补偿，成功地实现了百毫秒级的高效量子存储器。在高品质光与原子纠缠制备方面，我们确定了光子偏振及原子内态相结合的纠缠制备方案，通过仔细调节环形腔内的双折射效应，实现了具有高读出效率的光与原子纠缠。在多节点量子网络方面，我们搭建了三套冷光与原子纠缠装置，将三个单光子采用线性光学器件进行干涉，成功地制备了三个原子系综间的量子纠缠；我们还将三个原子系综用作三个单光子源，成功地实现了三个不同颜色光子间的量子干涉。以上研究内容为未来更多节点的远程量子网络奠定了基础，有望使得分布式量子计算等成为可能。