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领域之一。近年来，人们在理论上进行了许多努力，试图将这两个领域联合收割机结合起来。近年来的理论研究表明，利用原子系综进行量子信息处理在原理上是可行的。事实上，如何在实验上利用原子光学来实现量子信息的应用已经成为一个新的研究热点。在本项目中，我们将遵循最近的建议，通过利用激光脉冲和原子系综之间的相互作用，实验研究用原子系综和线性光学实现量子信息处理的可行性。特别是，我们将研究在气相中的原子系综的潜力，以建立量子中继器的长距离量子通信，即开发一种新的技术解决方案，量子中继器利用两个冷原子系综的有效量子比特型纠缠通过投影测量的单个光子的自发拉曼过程。在此基础上，我们将进一步研究集成冷原子和原子芯片的优点，以增强原子系综的相干性，并使量子中继器的小型化实现。我们希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.