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.
@article{arxiv.1306.6641,
title = {Long-distance distribution of genuine energy-time entanglement},
author = {A. Cuevas and G. Carvacho and G. Saavedra and J. Cariñe and W. A. T. Nogueira and M. Figueroa and A. Cabello and P. Mataloni and G. Lima and G. B. Xavier},
journal= {arXiv preprint arXiv:1306.6641},
year = {2014}
}