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arXiv:0706.4255 · Physical Review A

Quantum key distribution over 25 km with an all-fiber continuous-variable system

Jérôme Lodewyck, Matthieu R. Bloch, Raúl García−Patrón, Simon Fossier, Evgueni Karpov, Eleni Diamanti, Thierry Debuisschert, Nicolas J. Cerf, Rosa Tualle-Brouri, Steven W. McLaughlin, Philippe Grangier

Published Oct 3, 2007• 542 citations
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Abstract

We report on the implementation of a reverse-reconciliated coherent-state continuous-variable quantum key distribution system, with which we generated secret keys at a rate of more than $2\phantom{\rule{0.3em}{0ex}}\mathrm{kb}∕\mathrm{s}$ over $25\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ of optical fiber. Time multiplexing is used to transmit both the signal and phase reference in the same optical fiber. Our system includes all experimental aspects required for a field implementation of a quantum key distribution setup. Real-time reverse reconciliation is achieved by using fast and efficient low-density parity check error correcting codes.

DOI
10.1103/physreva.76.042305

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We report on the implementation of a reverse-reconciliated coherent-state continuous-variable quantum key distribution system, with which we generated secret keys at a rate of more than 2kb∕s2\phantom{\rule{0.3em}{0ex}}\mathrm{kb}∕\mathrm{s}2kb∕s over 25km25\phantom{\rule{0.3em}{0ex}}\mathrm{km}25km of optical fiber. Time multiplexing is used to transmit both the signal and phase reference in the same optical fiber. Our system includes all experimental aspects required for a field implementation of a quantum key distribution setup. Real-time reverse reconciliation is achieved by using fast and efficient low-density parity check error correcting codes.
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We have demonstrated a reverse reconciliation of a continuous-variable quantum key distribution system with efficient low-density parity check codes. A standard coded modulation technique, called Multi Level Coding/ Multistage Decoding scheme, is used to optimize the reconciliation. Via a numerical simulation, we get the results that efficiency of the reconciliation algorithm reaches 0.89 while the final secure key distribution rate of the whole system is more than 2.2 kbits/s over 20 km of single-mode optical fiber.
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Summary form only given. Continuous-variable quantum key distribution (CVQKD) is a promising alternative to commonly used discrete-variable QKD protocols, because this technology can be implemented with standard telecom components and recent results suggest that it will be compatible with standard wavelength division multiplexed telecommunication networks [1]. Security proofs against general eavesdropping attacks are available for CVQKD protocols using Gaussian modulation [2], and field implementations over deployed telecommunication networks have been demonstrated over the past few years [3].Long-distance operation of CVQKD systems, however, has been hindered until now by the limited efficiency of the complex error-correction (or reconciliation) algorithms that are required to extract the secret key from the correlated data shared by Alice and Bob. We have designed high-efficiency error correcting-codes [4] allowing to extract an errorless secret key in a CVQKD protocol using a Gaussian modulation of coherent states and a homodyne detection system. These codes are available for a wide range of signal-to-noise ratios on a Gaussian noise channel with a binary modulation and can be combined with a multidimensional reconciliation method [5]. This improved reconciliation procedure considerably extends the secure range of a continuous-variable quantum key distribution with Gaussian modulation.