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arXiv:1003.1056 · Physical Review A

Experimental study on discretely modulated continuous-variable quantum key distribution

Yong Shen, Hongxin Zou, Liang Tian, Ping‐Xing Chen, Jianmin Yuan

Published Aug 13, 2010• 51 citations
arXivHTMLPDF

Abstract

We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of $46.8$ kbits/s against collective attacks at an encoding rate of $10$ MHz for a $90%$ channel loss when the modulation variance is optimal.

DOI
10.1103/physreva.82.022317

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We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven that the phase noise in the source has no impact on the final secret key rate. In order to increase the encoding rate, we use broadband homodyne detectors and the no-switching protocol. In a realistic model, we establish a secret key rate of 46.846.846.8 kbits/s against collective attacks at an encoding rate of 101010 MHz for a 9090%90 channel loss when the modulation variance is optimal.
We realize an end-to-end no-switching quantum key distribution protocol using continuous-wave coherent light. We encode weak broadband Gaussian modulations onto the amplitude and phase quadratures of light beams. Our no-switching protocol achieves high secret key rate via a post-selection protocol that utilizes both quadrature information simultaneously. We establish a secret key rate of 25 Mbits/s for a lossless channel and 1 kbit/s for 90% channel loss, per 17 MHz of detected bandwidth, assuming individual Gaussian eavesdropping attacks. Since our scheme is truly broadband, it can potentially deliver orders of magnitude higher key rates by extending the encoding bandwidth with higher-end telecommunication technology.
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In this paper we propose a continuous-variable subcarrier wave quantum key distribution scheme with homodyne detection and present its security analysis in the finite-size regime. We calculate a lower bound on the secret key rate for the system under the assumption that the quantum channel noise is negligible compared to detector dark counts, and an eavesdropper is restricted to collective attacks. Our calculation shows that the current realistic system implementation would allow distributing a secret keys over channels with losses up to 9 dB.