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Quantum storage of photonic entanglement in a crystal


Entanglement is the fundamental characteristic of quantum physics—much experimental effort is devoted to harnessing it between various physical systems. In particular, entanglement between light and material systems is interesting owing to their anticipated respective roles as ‘flying’ and stationary qubits in quantum information technologies (such as quantum repeaters1,2,3 and quantum networks4). Here we report the demonstration of entanglement between a photon at a telecommunication wavelength (1,338 nm) and a single collective atomic excitation stored in a crystal. One photon from an energy–time entangled pair5 is mapped onto the crystal and then released into a well-defined spatial mode after a predetermined storage time. The other (telecommunication wavelength) photon is sent directly through a 50-metre fibre link to an analyser. Successful storage of entanglement in the crystal is proved by a violation of the Clauser–Horne–Shimony–Holt inequality6 by almost three standard deviations (S = 2.64 ± 0.23). These results represent an important step towards quantum communication technologies based on solid-state devices. In particular, our resources pave the way for building multiplexed quantum repeaters7 for long-distance quantum networks.

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Figure 1: Experimental set-up.
Figure 2: Non-classical correlations and storage efficiency.
Figure 3: Storage of photonic entanglement in a crystal.


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We thank R. Locher for help during the early stages of the experiment. We are grateful to A. Beveratos and W. Tittel for lending us avalanche photodiodes. This work was supported by the Swiss NCCR Quantum Photonics, the Science and Technology Cooperation Program Switzerland–Russia, as well as by the European projects QuRep and ERC-Qore. F.B. was supported in part by FQRNT.

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All authors contributed extensively to the work presented in this paper.

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Correspondence to Mikael Afzelius.

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Clausen, C., Usmani, I., Bussières, F. et al. Quantum storage of photonic entanglement in a crystal. Nature 469, 508–511 (2011).

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