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24 October 2016 Continuous operation of four-state continuous-variable quantum key distribution system
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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.
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Takuto Matsubara, Motoharu Ono, Yusuke Oguri, Tsubasa Ichikawa, Takuya Hirano, Kenta Kasai, Ryutaroh Matsumoto, and Toyohiro Tsurumaru "Continuous operation of four-state continuous-variable quantum key distribution system", Proc. SPIE 9996, Quantum Information Science and Technology II, 99960S (24 October 2016);

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