2013/06/30 by A. Cuevas, G. Carvacho, G. Saavedra +7
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1038/ncomms3871
published as Nat. Commun. 4, 2871 (2013) · 6 pages, 3 figures. Matches published version
arxiv created 2014/06/03 · arxiv updated 2014/06/04
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 fibers that is free of this geometrical loophole. This is achieved by adopting a new experimental design, and by using an actively stabilized fiber-based long interferometer. Our results represent an important step towards long-distance secure quantum communication in optical fibers.