Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125, USA.
Nature. 2010 Nov 18;468(7322):412-6. doi: 10.1038/nature09568.
Quantum networks are composed of quantum nodes that interact coherently through quantum channels, and open a broad frontier of scientific opportunities. For example, a quantum network can serve as a 'web' for connecting quantum processors for computation and communication, or as a 'simulator' allowing investigations of quantum critical phenomena arising from interactions among the nodes mediated by the channels. The physical realization of quantum networks generically requires dynamical systems capable of generating and storing entangled states among multiple quantum memories, and efficiently transferring stored entanglement into quantum channels for distribution across the network. Although such capabilities have been demonstrated for diverse bipartite systems, entangled states have not been achieved for interconnects capable of 'mapping' multipartite entanglement stored in quantum memories to quantum channels. Here we demonstrate measurement-induced entanglement stored in four atomic memories; user-controlled, coherent transfer of the atomic entanglement to four photonic channels; and characterization of the full quadripartite entanglement using quantum uncertainty relations. Our work therefore constitutes an advance in the distribution of multipartite entanglement across quantum networks. We also show that our entanglement verification method is suitable for studying the entanglement order of condensed-matter systems in thermal equilibrium.
量子网络由通过量子通道相干相互作用的量子节点组成，为科学提供了广阔的机会。例如，量子网络可以作为连接量子处理器进行计算和通信的“网络”，也可以作为允许通过通道介导的节点相互作用来研究量子临界现象的“模拟器”。量子网络的物理实现通常需要能够在多个量子存储器之间产生和存储纠缠态的动力学系统，并有效地将存储的纠缠态转移到量子通道中，以便在网络中分布。尽管已经在各种双体系统中演示了这些功能，但尚未实现能够“映射”存储在量子存储器中的多体纠缠到量子通道的互连。在这里，我们展示了在四个原子存储器中存储的测量诱导的纠缠；用户控制的，将原子纠缠相干地转移到四个光子通道；并使用量子不确定性关系对完整的四部分纠缠进行了表征。因此，我们的工作构成了在量子网络中分布多体纠缠的进展。我们还表明，我们的纠缠验证方法适用于研究处于热平衡的凝聚态系统的纠缠顺序。
