Postselection-Loophole-Free Bell Test Over an Installed Optical Fiber Network

G. Carvacho, Jaime CariƱe, Gabriel Saavedra Mondaca, A. Cuevas, Felipe Toledo, M. Figueroa, A. Cabello, Jan-Ake Larsson, P. Matalloni, G. Lima and G. B. Xavier


Device-independent quantum communication will require a loophole-free violation of Bell inequalities. In typical scenarios where line of sight between the communicating parties is not available, it is convenient to use energy-time entangled photons due to intrinsic robustness while propagating over optical fibers. Here we show an energy-time Clauser-Horne-Shimony-Holt Bell inequality violation with two parties separated by 3.7 km over the deployed optical fiber network belonging to the University of ConcepciĆ³n in Chile. Remarkably, this is the first Bell violation with spatially separated parties that is free of the postselection loophole, which affected all previous in-field long-distance energy-time experiments. Our work takes a further step towards a fiber-based loophole-free Bell test, which is highly desired for secure quantum communication due to the widespread existing telecommunication infrastructure


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