Entanglement distribution over 150 km in wavelength division multiplexed channels for quantum cryptography

• Published in: Laser & photonics reviews 2016-05, Vol.10 (3), p.451-457
• Main Authors: Aktas, Djeylan, Fedrici, Bruno, Kaiser, Florian, Lunghi, Tommaso, Labonté, Laurent, Tanzilli, Sébastien
• Format: Article
• Language: English
• Subjects: Channels; Cryptography; Data encryption; Demultiplexing; Entanglement; Entanglement-based quantum cryptography; Fiber optics communication; Fibers; Multiplexing; Non-linear optics; Photonics; Physics; Quantum cryptography; Quantum information and processing; Quantum photonics; Quantum Physics; Strategy
• ISSN: 1863-8880; 1863-8899
• DOI: 10.1002/lpor.201500258

Granting information privacy is of crucial importance in our society, notably in fiber communication networks. Quantum cryptography provides a unique means to establish, at remote locations, identical strings of genuine random bits, with a level of secrecy unattainable using classical resources. However, several constraints, such as non‐optimized photon number statistics and resources, detectors' noise, and optical losses, currently limit the performances in terms of both achievable secret key rates and distances. Here, these issues are addressed using an approach that combines both fundamental and off‐the‐shelves technological resources. High‐quality bipartite photonic entanglement is distributed over a 150 km fiber link, exploiting a wavelength demultiplexing strategy implemented at the end‐user locations. It is shown how coincidence rates scale linearly with the number of employed telecommunication channels, with values outperforming previous realizations by almost one order of magnitude. Thanks to its potential of scalability and compliance with device‐independent strategies, this system is ready for real quantum applications, notably entanglement‐based quantum cryptography. In a fiber quantum network, a source emits broadband, i.e. multiplexed, entangled photons. Via routing stages, those are distributed to multiple pairs of remote users in spectrally correlated pairs of standard telecommunication channels. Additional demultiplexing stages at the end‐stations allow each two‐partner to obtain an overall detection rate increase equal to the number of exploited channel pairs. This strategy can straightforwardly be applied to high bit‐rate quantum key distribution systems.