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Updated: May 5, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Long-distance distribution of genuine energy-time entanglement
A Cuevas1, G Carvacho, G Saavedra
11] 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].
Abstract:
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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