Article,
Entanglement of spin waves among four quantum memories
Nature, 468 (7322): 412--416 (Nov 18, 2010)
DOI: 10.1038/nature09568
Abstract
Quantum networks are composed of quantum nodes that interact coherently through quantum channels, and open a broad frontier of scientific opportunities1. For example, a quantum network can serve as a 'web' for connecting quantum processors for computation2, 3 and communication4, or as a 'simulator' allowing investigations of quantum critical phenomena arising from interactions among the nodes mediated by the channels5, 6. 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 systems7, 8, 9, 10, 11, 12, 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 relations13, 14, 15, 16. 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 equilibrium17, 18.
