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Nat Commun. 2013;4:2871. doi: 10.1038/ncomms3871.

Long-distance distribution of genuine energy-time entanglement.

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1] Departamento de Física, Universidad de Concepción, 160-C, Concepción 4070386, Chile [2] Center for Optics and Photonics, Universidad de Concepción, Concepción 4070386, Chile [3] MSI-Nucleus for Advanced Optics, Universidad de Concepción, Concepción 4070386, Chile [4].


Any practical realization of entanglement-based quantum communication must be intrinsically secure and able to span long distances avoiding the need of a straight line between the communicating parties. The violation of Bell's inequality offers a method for the certification of quantum links without knowing the inner workings of the devices. Energy-time entanglement quantum communication satisfies all these requirements. However, currently there is a fundamental obstacle with the standard configuration adopted: an intrinsic geometrical loophole that can be exploited to break the security of the communication, in addition to other loopholes. Here we show the first experimental Bell violation with energy-time entanglement distributed over 1 km of optical fibres that is free of this geometrical loophole. This is achieved by adopting a new experimental design, and by using an actively stabilized fibre-based long interferometer. Our results represent an important step towards long-distance secure quantum communication in optical fibres.

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