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arXiv:quant-ph/0511104 · Physical Review A

Controlling excess noise in fiber-optics continuous-variable quantum key distribution

Jérôme Lodewyck, Thierry Debuisschert, Rosa Tualle-Brouri, Philippe Grangier

Published Nov 22, 2005• 119 citations
arXivHTMLPDF

Abstract

We describe a continuous-variable coherent-states quantum-key distribution system working at $1550\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and entirely made of standard fiber optics and telecommunications components, such as integrated-optics modulators, couplers and fast InGaAs photodiodes. The setup is composed of an emitter randomly modulating a coherent state in the complex plane with a doubly Gaussian distribution, and a receiver based on a shot-noise limited time-resolved homodyne detector. By using a reverse reconciliation protocol, the device can transfer a raw key rate up to $1\phantom{\rule{0.3em}{0ex}}\mathrm{Mbit}∕\mathrm{s}$, with a proven security against Gaussian or non-Gaussian attacks. The dependence of the secret information rate of the present fiber setup is studied as a function of the line transmission and excess noise.

DOI
10.1103/physreva.72.050303

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Abstract Secret key rate is a core performance indicator in implementing quantum key distribution, which directly determines the transmission rate of enciphered data. Here we demonstrate a high-key-rate quantum key distribution system over mature telecom components. The entire framework of quantum key distribution over these components is constructed. The high-rate low-noise Gaussian modulation of coherent states is realized by a classical electro-optic IQ modulator. High-baud low-intensity quantum signals are received by a commercial integrated coherent receiver under the shot-noise limit. A series of digital signal processing algorithms are proposed to achieve accurate signal recovery and key distillation. The system has yield a secret key rate of 10.37 Mbps, 1.61 Mbps, 337.82 kbps, and 58.06 kbps under the standard telecom fiber of 20 km, 50 km, 70 km, and 100 km, respectively. Our results represent the achieved highest secret key generation rate for quantum key distribution using continuous variables at a standard telecom wavelength. Moreover, it breaks the isolation between quantum communication and classical optical communication in terms of components, and opens the way to a high-speed and cost-effective formation of metropolitan quantum secure communication networks.
We report on the development of continuous-variable quantum key distribution (CV-QKD) system that are based on discrete quadrature amplitude modulation (QAM) and homodyne detection of coherent states of light. We use a pulsed light source whose wavelength is 1550 nm and repetition rate is 10 MHz. The CV-QKD system can continuously generate secret key which is secure against entangling cloner attack. Key generation rate is 50 kbps when the quantum channel is a 10 km optical fiber. The CV-QKD system we have developed utilizes the four-state and post-selection protocol [T. Hirano, et al., Phys. Rev. A 68, 042331 (2003).]; Alice randomly sends one of four states {|±α⟩,|±𝑖α⟩}, and Bob randomly performs x- or p- measurement by homodyne detection. A commercially available balanced receiver is used to realize shot-noise-limited pulsed homodyne detection. GPU cards are used to accelerate the software-based post-processing. We use a non-binary LDPC code for error correction (reverse reconciliation) and the Toeplitz matrix multiplication for privacy amplification.