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China-Ireland International Conference on Information and Communications Technologies (CIICT)

Simulation study on reverse reconciliation of a continuous variable quantum key distribution system

Kang Li, Li Yu, Bojun Yang

Published Jan 1, 2008• 0 citations
Publisher

Abstract

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.

DOI
10.1049/cp:20080838

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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.
Based on the Multilevel Codes/Multistage Decoding system,we achieved the reverse reconciliation for continuous variable quantum key distribution.Firstly,we show how to select the optimal quantization interval by maximizing the mutual information between the communicating parties.Then the optimal rate of each equivalent channel is calculated at the SNR level of 4 dB.The low-density parity check(LDPC) code is chosen as the channel codes,and the reverse reconciliation utilize a side-information based LDPC iterative decoding algorithm.
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.
Abstract Quantum key distribution (QKD) is the most mature application of quantum information technology. Information reconciliation is a crucial step in QKD and significantly affects the final secret key rates shared between two legitimate parties. We analyze and compare various construction methods of low-density parity-check (LDPC) codes and design high-performance irregular LDPC codes with a block length of 10 6 . Starting from these good codes and exploiting the slice reconciliation technique based on multilevel coding and multistage decoding, we realize high-efficiency Gaussian key reconciliation with efficiency higher than 95% for signal-to-noise ratios above 1. Our demonstrated method can be readily applied in continuous variable QKD.
Continuous-variable quantum key distribution (QKD) utilizes an ensemble of coherent states of light to distribute secret encryption keys between two parties. An essential ingredient of the QKD protocol is highly efficient information reconciliation. To achieve highly efficient reconciliation, error-correcting codes with a low channel coding rate are inevitable in the most common schemes of multilevel coding and multistage decoding (MLC-MSD) and multidimensional reconciliation. Multiedge-type (MET) low-density parity-check (LDPC) codes are well suited for highly efficient reconciliation at low rates. Here, we calculate the optimal channel coding rates in the MLC-MSD scheme for reverse reconciliation, introduce the concept of generalized extrinsic information transfer charts for MET-LDPC codes, which constitute a simple and fast asymptotic analysis tool, and present a set of MET-LDPC codes with asymptotic efficiency >97>97%>97 for channel coding rates 0.1, 0.05, 0.02, and 0.01. We believe that our codes will find wide application in implementations of continuous-variable quantum key distribution based on Gaussian modulation.
Discrete modulation continuous-variable quantum key distribution protocols are compatible with modern coherent optical communication technologies and devices. As a key part of the protocol, the performance of information reconciliation directly affects the secret key rate and transmission distance. Herein, we propose a reconciliation scheme for hard-decision strategy--based discrete modulation continuous-variable quantum key distribution protocol with eight-phase shift keying by combining slice reconciliation and raptor-like low-density parity-check (RL-LDPC) codes. We design the optimal binary sequence encoding of the discretized values of the receiver and sender, which reduce both the number of levels of error correction and the reconciliation complexity. In order to reduce the frame error rate, both the degree distribution and the size of the base matrix of RL-LDPC code is optimized. Simulation results show that the proposed scheme can reach reconciliation efficiencies of 92.05% and 93% with frame error rates of 6.2% and 11.7% at the signal-to-noise ratio of 0.15, respectively. At these points, the key rates can reach 0.0193 and 0.0195 bits/pulse, respectively.
Reconciliation is a significant procedure in a continuous-variable quantum key distribution (CV-QKD) system. It is employed to extract secure secret key from the resulted string through quantum channel between two users. However, the efficiency and the speed of previous reconciliation algorithms are low. These problems limit the secure communication distance and the secure key rate of CV-QKD systems. In this paper, we proposed a high-speed reconciliation algorithm through employing a well-structured decoding scheme based on low density parity-check (LDPC) code. The complexity of the proposed algorithm is reduced obviously. By using a graphics processing unit (GPU) device, our method may reach a reconciliation speed of 25 Mb/s for a CV-QKD system, which is currently the highest level and paves the way to high-speed CV-QKD.