Experimental purification of two-atom entanglement

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Entanglement is a necessary resource for quantum applications—entanglement established between quantum systems at different locations enables private communication1 and quantum teleportation2, and facilitates quantum information processing3. Distributed entanglement is established by preparing an entangled pair of quantum particles in one location, and transporting one member of the pair to another location. However, decoherence during transport reduces the quality (fidelity) of the entanglement. A protocol to achieve entanglement ‘purification’ has been proposed4 to improve the fidelity after transport. This protocol uses separate quantum operations at each location and classical communication to distil high-fidelity entangled pairs from lower-fidelity pairs. Proof-of-principle experiments distilling entangled photon pairs have been carried out5,6,7,8,9. However, these experiments obtained distilled pairs with a low probability of success and required destruction of the entangled pairs, rendering them unavailable for further processing. Here we report efficient and non-destructive entanglement purification4 with atomic quantum bits. Two noisy entangled pairs were created and distilled into one higher-fidelity pair available for further use. Success probabilities were above 35 per cent. The many applications of entanglement purification make it one of the most important techniques in quantum information processing.

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Figure 1: Network diagrams for purification.
Figure 2: Purified fidelity as a function of unpurified fidelity.


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This work was supported by the Disruptive Technology Office (DTO), by a DoD Multidisciplinary University Research Initiative (MURI) programme administered by the Office of Naval Research and by NIST. R.R. was supported by the Alexander von Humboldt Foundation. We thank S. Glancy and W. Itano for comments on the manuscript.

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Correspondence to D. Leibfried.

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Reichle, R., Leibfried, D., Knill, E. et al. Experimental purification of two-atom entanglement. Nature 443, 838–841 (2006) doi:10.1038/nature05146

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