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Experimental demonstration of continuous-variable quantum key distribution over 80 km of standard telecom fiber

Paul Jouguet, Sébastien Kunz-Jacques, Anthony Leverrier, Philippe Grangier, Eleni Diamanti

Published Jan 1, 2013• 3 citations
Publisher

Abstract

Continuous-variable quantum key distribution (CVQKD) [1] 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 [2]. Security proofs against general eavesdropping attacks are available for CVQKD protocols using Gaussian modulation [3], and field implementations over deployed telecommunication networks have been demonstrated over the past few years [4].

DOI
10.1364/cleo_qels.2013.qtu2c.4

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Continuous-variable quantum key distribution (CVQKD) [1] 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 [2]. Security proofs against general eavesdropping attacks are available for CVQKD protocols using Gaussian modulation [3], and field implementations over deployed telecommunication networks have been demonstrated over the past few years [4].
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.
Quantum key distribution (QKD) enables the establishment of secret keys between users connected via a channel vulnerable to eavesdropping, with information-theoretic security, that is, independently of the power of a malevolent party [1]. QKD systems based on the encoding of the key information on continuous variables (CV), such as the values of the quadrature components of coherent states [2], [3], present the major advantage that they only require standard telecommunication technology. However, the most general security proofs for CVQKD required until now the use of Gaussian modulation by the transmitter, complicating practical implementations [4]–[6]. Here, we experimentally implement a protocol that allows for arbitrary, Gaussian-like, discrete modulations, whose security is based on a theoretical proof that applies generally to such situations [7]. These modulation formats are compatible with the use of powerful tools of coherent optical telecommunication, allowing our system to reach an estimated performance of tens of megabit per second secret key rates over 25 km
We report on what we believe is the first field implementation of a continuous-variable quantum key distribution (CV-QKD) network with point-to-point configuration. Four QKD nodes are deployed on standard communication infrastructures connected with commercial telecom optical fiber. Reliable key exchange is achieved in the wavelength-division-multiplexing CV-QKD network. The impact of a complex and volatile field environment on the excess noise is investigated, since excess noise controlling and reduction is arguably the major issue pertaining to distance and the secure key rate. We confirm the applicability and verify the maturity of the CV-QKD network in a metropolitan area, thus paving the way for a next-generation global secure communication network.
Continuous variable quantum key distribution (CVQKD) uses the continuous quadratures of light to share a secret key between a transmitter and receiver. The presence of an eavesdropper can be detected by fundamental quantum mechanics. Compared to the more established discrete variable QKD, CVQKD uses more cost-effective homodyne detectors which are more compatible with current telecommunication technologies. In a future global quantum network, CVQKD could be used to ensure the secure exchange of information. In this work, the feasibility of a variety of CVQKD protocols in different channels that could be used to establish a global quantum network are studied. These are the Gaussian modulated and discrete modulated CVQKD protocols for satellite to optical ground station downlinks and uplinks for Earth-space connections, inter-satellite links for space connections, satellite to ship and underwater links for maritime connections, and fibre network links for terrestrial connections. Secret key distribution between continents and various regions is simulated while accounting for the different adverse effects associated with each link. The combination of these connections with routing and scheduling ensures inter-continental high-speed information exchange with unconditional security that is required to achieve the goal of a global quantum network.
We report the first continuous-variable quantum key distribution (CVQKD) experiment to enable the creation of 1 Mbps secure key rate over 25 km standard telecom fiber in a coarse wavelength division multiplexers (CWDM) environment. The result is achieved with two major technological advances: the use of a 1 GHz shot-noise-limited homodyne detector and the implementation of a 50 MHz clock system. The excess noise due to noise photons from local oscillator and classical data channels in CWDM is controlled effectively. We note that the experimental verification of high-bit-rate CVQKD in the multiplexing environment is a significant step closer toward large-scale deployment in fiber networks.
Abstract Establishing secure data communication necessitates secure key exchange over a public channel. Quantum key distribution (QKD), which leverages the principles of quantum physics, can achieve this with information-theoretic security. The discrete modulated (DM) continuous variable (CV) QKD protocol, in particular, is a suitable candidate for large-scale deployment of quantum-safe communication due to its simplicity and compatibility with standard high-speed telecommunication technology. Here, we present the first experimental demonstration of a four-state DM CVQKD system, successfully generating composable finite-size keys, secure against collective attacks over a 20 km fiber channel with 2.3 × 109 coherent quantum states, achieving a positive composable key rate of 11.04 × 10−3 bits/symbol. This accomplishment is enabled by using an advanced security proof, meticulously selecting its parameters, and the fast, stable operation of the system. Our results mark a significant step toward the large-scale deployment of practical, high-performance, cost-effective, and highly secure quantum key distribution networks using standard telecommunication components.