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Experimental demonstration of a heralded entanglement source


The heralded generation of entangled states is a long-standing goal in quantum information processing, because it is indispensable for a number of quantum protocols1,2. Polarization entangled photon pairs are usually generated through spontaneous parametric down-conversion3, but the emission is probabilistic. Their applications are generally accompanied by post-selection and destructive photon detection. Here, we report a source of entanglement generated in an event-ready manner by conditioned detection of auxiliary photons4. This scheme benefits from the stable and robust properties of spontaneous parametric down-conversion and requires only modest experimental efforts. It is flexible and allows the preparation efficiency to be significantly improved by using beamsplitters with different transmission ratios. We have achieved a fidelity better than 87% and a state preparation efficiency of 45% for the source. This could offer promise in essential photonics-based quantum information tasks, and particularly in enabling optical quantum computing by reducing dramatically the computational overhead5,6.

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Figure 1: Schematic set-up.
Figure 2: Experimental set-up for an event-ready entanglement source.
Figure 3: Efficiency of state preparation.
Figure 4: Experimental data for fidelity measurements.

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This work was supported by the European Commission through the European Research Council (ERC) Grant and the Specific Targeted Research Projects (STREP) project Hybrid Information Processing (HIP), the Chinese Academy of Sciences, the National Fundamental Research Program of China under grant no. 2006CB921900, and the National Natural Science Foundation of China. C.W. was additionally supported by the Schlieben-Lange Program of the ESF. The authors are grateful to Dr Xian-Min Jin for help in improving the figures.

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C.W., X.-H.B., Y.-A.C., Q.Z. and J.-W.P. designed the experiment. C.W., C.-M.L., A.R., A.G., Y.-A.C. and K.C. performed the experiment. C.W., C.-M.L., A.R., X.-H.B., K.C. and J.-W.P. analysed the data. C.W., C.-M.L., K.C. and J.-W.P. wrote the paper.

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Correspondence to Kai Chen or Jian-Wei Pan.

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The authors declare no competing financial interests.

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Wagenknecht, C., Li, CM., Reingruber, A. et al. Experimental demonstration of a heralded entanglement source. Nature Photon 4, 549–552 (2010).

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