A. Cuevas, G. Carvacho, G. Saavedra, J. Cariñe, W. A. T. Nogueira, M. Figueroa, A. Cabello, P. Mataloni, G. Lima, G. B. Xavier
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 relying on any physical assumptions. Energy-time entanglement quantum communication satisfies all these requirements. However, currently there is a fundamental obstacle with the standard configuration adopted. It has an intrinsic geometrical loophole that can be exploited to break the security of the communication. Here we show the first experimental Bell violation with energy-time entanglement distributed over 1 km of optical fibers that is free of this geometrical loophole. This is achieved by adopting the new "hug" configuration for energy-time entanglement, and by using an actively stabilized fiber-based long interferometer. Our result represents an important step towards long-distance secure quantum communication in optical fibers.
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http://arxiv.org/abs/1306.6641
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