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Measurement-induced entanglement for excitation stored in remote atomic ensembles

Abstract

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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Figure 1: An overview of our experiment to entangle two atomic ensembles is shown.
Figure 2: Coherence between the atomic ensembles L, R induced by a measurement event of the fields 1L and 1R at detector D1a or D1b.
Figure 3: Inference of the concurrence C z i (a) and density matrix (b) at the three locations z i indicated in Fig. 1b.

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Acknowledgements

We gratefully acknowledge J. Hall and J. Ye for discussions about phase stabilization. This research is supported by the Advanced Research and Development Activity (ARDA), by the National Science Foundation, and by the Caltech MURI Center for Quantum Networks. D.F. acknowledges financial support by CNPq (Brazilian agency). H.d.R. acknowledges financial support by the Swiss National Science Foundation. S.J.v.E. thanks L. Huelsbergen for assistance in computer matters.

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Chou, C., de Riedmatten, H., Felinto, D. et al. Measurement-induced entanglement for excitation stored in remote atomic ensembles. Nature 438, 828–832 (2005). https://doi.org/10.1038/nature04353

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