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.
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
Quantum key distribution （QKD） is a major research topic because it provides unconditional security. Unfortunately, many imperfections remain in QKD＇s experimental realization. The Faraday-Michelson （FM） QKD system is proposed to eliminate these imperfections using polarization. However, the long arm＇s phase modulator （PM） has an unexpected insertion loss, meaning that the state sent is no longer perfect. In this letter, we propose an alternative FM-QKD system structure, and analyze the security and key generation rate in comparison with the original system via different analysis methods. We find an obvious key rate improvement when the PM insertion loss is not extremely small.
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.
In the original BB84 quantum key distribution protocol, the states are prepared and measured randomly, which lose the unmatched detection results. To improve the sifting efficiency, biased bases selection BB84 protocol is proposed. Meanwhile, a practical quantum key distribution protocol can only transmit a finite number of signals, resulting in keys of finite length. The previous techniques for finite-key analysis focus mainly on the statistical fluctuations of the error rates and yields of the qubits. However, the prior choice probabilities of the two bases also have fluctuations by taking into account the finite-size effect. In this paper, we discuss the security of biased decoy state BB84 protocol with finite resources by considering all of the statistical fluctuations. The results can be directly used in the experimental realizations.
To improve the security of the smart grid, quantum key distribution（QKD） is an excellent choice. The rapid fluctuations on the power aerial optical cable and electromagnetic disturbance in substations are two main challenges for implementation of QKD. Due to insensitivity to birefringence of the channel, the stable phase-coding Faraday–Michelson QKD system is very practical in the smart grid. However, the electromagnetic disturbance in substations on this practical QKD system should be considered. The disturbance might change the rotation angle of the Faraday mirror, and would introduce an additional quantum bit error rate（QBER）. We derive the new fringe visibility of the system and the additional QBER from the electromagnetic disturbance. In the worst case, the average additional QBER only increases about 0.17% due to the disturbance, which is relatively small to normal QBER values. We also find the way to degrade the electromagnetic disturbance on the QKD system.
Recently, the Hong-Ou-Mandel （HOM） interference between two independent weak coherent pulses （WCPs） has been paid much attention due to the measurement-device-independent （MDI） quantum key distribution （QKD）. Using classical wave theory, articles reported before show that the visibility of this kind of HOM-type interference is 〈 50%. In this work, we analyze this kind of interference using quantum optics, which reveals more details compared to the wave theory. Analyses confirm the maximum visibility of 50%. And we conclude that the maximum visibility of 50% comes from the two single-photon states in WCPs, without considering the noise. In the experiment, we successfully approach the visibility of 50% by using WCPs splitting from the single pico-second laser source and phase scanning. Since this kind of HOM interference is immune to slow phase fluctuations, both the realized and proposed experiment designs can provide stable ways of high-resolution optical distance detection.
In a practical quantum key distribution（QKD） system, imperfect equipment, especially the single-photon detector,can be eavesdropped on by a blinding attack. However, the original blinding attack may be discovered by directly detecting the current. In this paper, we propose a probabilistic blinding attack model, where Eve probabilistically applies a blinding attack without being caught by using only an existing intuitive countermeasure. More precisely, our countermeasure solves the problem of how to define the bound in the limitation of precision of current detection, and then we prove security of the practical system by considering the current parameter. Meanwhile, we discuss the bound of the quantum bit error rate（QBER） introduced by Eve, by which Eve can acquire information without the countermeasure.
We report an adjustable unbalanced quantum random-number generator based on the polarization of photons,which can produce nondeterministic true random unbalanced numbers. The underlying physical process is inherently quantum mechanical. To prove the quality of the output sequence of the proposed generator, we test the obtained bias-free sequence through the 3-standard-deviation criteria and the National Institutes of Standards and Technology test suite. Another type of nondeterministic unbalanced random-number generator is also studied in this work, to evaluate the quality of the output biased random numbers.
