Letter

Nature 454, 1098-1101 (28 August 2008) | doi:10.1038/nature07241; Received 9 March 2008; Accepted 3 July 2008

Experimental demonstration of a BDCZ quantum repeater node

Zhen-Sheng Yuan1,2,4, Yu-Ao Chen1,2,4, Bo Zhao1, Shuai Chen1, Jörg Schmiedmayer3 & Jian-Wei Pan1,2

  1. Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany
  2. Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
  3. Atominstitut der Österreichischen Universitäten, TU-Wien, A-1020 Vienna, Austria
  4. These authors contributed equally to this work.

Correspondence to: Yu-Ao Chen1,2,4Jian-Wei Pan1,2 Correspondence and requests for materials should be addressed to Y.-A.C. (Email: yuao@physi.uni-heidelberg.de) or J.-W.P. (Email: jian-wei.pan@physi.uni-heidelberg.de).

Quantum communication is a method that offers efficient and secure ways for the exchange of information in a network. Large-scale quantum communication1, 2, 3, 4 (of the order of 100 km) has been achieved; however, serious problems occur beyond this distance scale, mainly due to inevitable photon loss in the transmission channel. Quantum communication eventually fails5 when the probability of a dark count in the photon detectors becomes comparable to the probability that a photon is correctly detected. To overcome this problem, Briegel, Dür, Cirac and Zoller (BDCZ) introduced the concept of quantum repeaters6, combining entanglement swapping7 and quantum memory to efficiently extend the achievable distances. Although entanglement swapping has been experimentally demonstrated8, the implementation of BDCZ quantum repeaters has proved challenging owing to the difficulty of integrating a quantum memory. Here we realize entanglement swapping with storage and retrieval of light, a building block of the BDCZ quantum repeater. We follow a scheme9, 10 that incorporates the strategy of BDCZ with atomic quantum memories11. Two atomic ensembles, each originally entangled with a single emitted photon, are projected into an entangled state by performing a joint Bell state measurement on the two single photons after they have passed through a 300-m fibre-based communication channel. The entanglement is stored in the atomic ensembles and later verified by converting the atomic excitations into photons. Our method is intrinsically phase insensitive and establishes the essential element needed to realize quantum repeaters with stationary atomic qubits as quantum memories and flying photonic qubits as quantum messengers.

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