Quantum information processing with linear optics and atomic ensembles

量子信息科学和原子光学是现代物理学中最活跃的两个领域。近年来，人们在理论方面做出了许多努力，试图将这两个领域结合起来。最近的理论进展表明，原则上有可能用原子系综进行量子信息处理。事实上，如何通过实验开发原子光学在量子信息中的应用已经成为一个新的研究热点。在这个项目中，我们将遵循最近的建议，实验研究利用激光脉冲和原子系综之间的相互作用，利用原子系综和线性光学实现量子信息处理的可行性。特别强调的是，我们将研究原子系综在气相中的潜力，以建立远距离量子通信的量子中继器，也就是说，通过自发拉曼过程对单个光子的投影测量，利用两个冷原子系综的有效量子比特型纠缠，为量子中继器开发一种新的技术解决方案。在此基础上，我们将进一步研究将冷原子集成到原子芯片中的优势，以增强原子系综的相干性和实现量子中继器的小型化。我们期望量子中继器的实现将为长距离量子通信开辟现实的前景。在实验中开发的技术也将在原子和光子的各种量子信息协议中有许多有用的应用。

Quantum information science and atom optics are among the most active fields in modern physics. In recent years, many theoretical efforts have been made to combine these two fields. Recent theoretical progresses have shown the in-principle possibility to perform quantum information processing with atomic ensembles. Indeed, how to experimentally exploit atom optics for quantum information applications has become a new focus of research. In this project, we will follow the recent proposals to experimentally investigate the feasibility of implementing quantum information processing with atomic ensembles and linear optics by utilizing the interaction between laser pulses and atomic ensembles. With particular emphasis, we will investigate the potentials of atomic ensembles in the gas phase to build quantum repeaters for long-distance quantum communication, that is, to develop a new technological solution for quantum repeaters making use of the efficient qubit-type entanglement of two cold atomic ensembles by a projective measurement of individual photons by spontaneous Raman processes. On this basis, we will further investigate the advantages of integrating cold atoms an atom chips both to enhance the coherence of atomic ensembles and to enable a miniaturized realization of quantum repeaters. We expect that an implementation of quantum repeaters would open up realistic prospective for quantum communication over long distances. The techniques that will be developed in the experiments would also have many useful applications in various quantum information protocols with atoms and photons.