Letter

Nature 438, 828-832 (8 December 2005) | doi:10.1038/nature04353; Received 31 August 2005; Accepted 19 October 2005

Measurement-induced entanglement for excitation stored in remote atomic ensembles

C. W. Chou1, H. de Riedmatten1, D. Felinto1, S. V. Polyakov1, S. J. van Enk2 & H. J. Kimble1

  1. Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125, USA
  2. Bell Labs, Lucent Technologies, Room 1D-428, 600-700 Mountain Avenue, Murray Hill, New Jersey 07974, USA

Correspondence to: H. J. Kimble1 Correspondence and requests for materials should be addressed to H.J.K. (Email: hjkimble@caltech.edu).

A critical requirement for diverse applications in quantum information science is the capability to disseminate quantum resources over complex quantum networks1, 2. For example, the coherent distribution of entangled quantum states together with quantum memory (for storing the states) can enable scalable architectures for quantum computation3, communication4 and metrology5. Here we report observations of entanglement between two atomic ensembles located in distinct, spatially separated set-ups. Quantum interference in the detection of a photon emitted by one of the samples projects the otherwise independent ensembles into an entangled state with one joint excitation stored remotely in 105 atoms at each site6. After a programmable delay, we confirm entanglement by mapping the state of the atoms to optical fields and measuring mutual coherences and photon statistics for these fields. We thereby determine a quantitative lower bound for the entanglement of the joint state of the ensembles. Our observations represent significant progress in the ability to distribute and store entangled quantum states.

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