Post-processing is indispensable in quantum key distribution(QKD), which is aimed at sharing secret keys between two distant parties. It mainly consists of key reconciliation and privacy amplification, which is used for sharing the same keys and for distilling unconditional secret keys. In this paper, we focus on speeding up the privacy amplification process by choosing a simple multiplicative universal class of hash functions. By constructing an optimal multiplication algorithm based on four basic multiplication algorithms, we give a fast software implementation of length-adaptive privacy amplification. "Length-adaptive" indicates that the implementation of privacy amplification automatically adapts to different lengths of input blocks. When the lengths of the input blocks are 1 Mbit and 10 Mbit, the speed of privacy amplification can be as fast as 14.86 Mbps and 10.88 Mbps, respectively. Thus, it is practical for GHz or even higher repetition frequency QKD systems.
In the recent work of Kiss et al.[Phys.Rev.Lett.107(2011)100501],the evolvement of two-qubit quantum states in a measurement-based purification process is studied.As they pointed out,the purification results manifest sensitivity to the applied initial states.The convergence regions to different stable circles are depicted on a complex plane.Because of the result patterns'likeness to typical fractals,we make further study on the interesting patterns'connection to fractals.Finally,through a numerical method we conclude that the boundaries of different islands of the patterns are fractals,which possess a non-integral fractal dimension.Also,we show that the fractal dimension would vary with the change of the portion of the noise added to the initial states.
In a quantum key distribution(QKD)system,the error rate needs to be estimated for determining the joint probability distribution between legitimate parties,and for improving the performance of key reconciliation.We propose an efficient error estimation scheme for QKD,which is called parity comparison method(PCM).In the proposed method,the parity of a group of sifted keys is practically analysed to estimate the quantum bit error rate instead of using the traditional key sampling.From the simulation results,the proposed method evidently improves the accuracy and decreases revealed information in most realistic application situations.
Measurement-device-independent quantum key distribution(MDI-QKD) is aimed at removing all detector side channel attacks,while its security relies on the assumption that the encoding systems including sources are fully characterized by the two legitimate parties. By exploiting the mismatched-basis statistics in the security analysis, MDI-QKD even with uncharacterized qubits can generate secret keys. In this paper, considering the finite size effect, we study the decoy-state MDI-QKD protocol with mismatchedbasis events statistics by performing full parameter optimization, and the simulation result shows that this scheme is very practical.
Quantum key distribution(QKD)provides an unconditional secure key generation method between two distant legitimate parties Alice and Bob based on the fundamental properties of quantum mechanics,in the presence of an eavesdropper Eve.Since key reconciliation cannot always assure that the reconciled keys between Alice and Bob are identical,error verification is an important step in QKD.In this paper,we propose a scheme of delayed error verification using extra keys gained by privacy amplification with an arbitrarily small failure probability.The proposed scheme simplifies the post-processing procedure in QKD,which can be applied in practical QKD systems.
Chun-Mei ZhangXiao-Tian SongPatcharapong TreeviriyanupabMo LiChao WangHong-Wei LiZhen-Qiang YinWei ChenZheng-Fu Han
