Effect of weak randomness flaws on security evaluation of practical quantum key distribution with distinguishable decoy states

Quantum key distribution provides an unconditional secure key sharing method in theory,but the imperfect factors of practical devices will bring security vulnerabilities.In this paper,we characterize the imperfections of the sender and analyze the possible attack strategies of Eve.Firstly,we present a quantized model for distinguishability of decoy states caused by intensity modulation.Besides,considering that Eve may control the preparation of states through hidden variables,we evaluate the security of preparation in practical quantum key distribution(QKD)scheme based on the weak-randomness model.Finally,we analyze the influence of the distinguishability of decoy state to secure key rate,for Eve may conduct the beam splitting attack and control the channel attenuation of different parts.Through the simulation,it can be seen that the secure key rate is sensitive to the distinguishability of decoy state and weak randomness,especially when Eve can control the channel attenuation.

Security analysis of satellite-to-ground reference-frame-independent quantum key distribution with beam wandering

The reference-frame-independent(RFI)quantum key distribution(QKD)is suitable for satellite-based links by removing the active alignment on the reference frames.However,how the beam wandering influences the performance of RFI-QKD remains a pending issue in satellite-to-ground links.In this paper,based on the mathematical model for characterizing beam wandering,we present the security analysis for satellite-to-ground RFI-QKD and analytically derive formulas for calculating the secret key rate with beam wandering.Our simulation results show that the performance of RFI-QKD is better than the Bennett–Brassard 1984(BB84)QKD with beam wandering in asymptotic case.Furthermore,the degree of influences of beam wandering is specifically presented for satellite-to-ground RFI-QKD when statistical fluctuations are taken into account.Our work can provide theoretical support for the realization of RFI-QKD using satellite-to-ground links and have implications for the construction of large-scale satellite-based quantum networks.

Reference-frame-independent quantum key distribution with two-way classical communication

The data post-processing scheme based on two-way classical communication(TWCC)can improve the tolerable bit error rate and extend the maximal transmission distance when used in a quantum key distribution(QKD)system.In this study,we apply the TWCC method to improve the performance of reference-frame-independent quantum key distribution(RFI-QKD),and analyze the influence of the TWCC method on the performance of decoy-state RFI-QKD in both asymptotic and non-asymptotic cases.Our numerical simulation results show that the TWCC method is able to extend the maximal transmission distance from 175 km to 198 km and improve the tolerable bit error rate from 10.48%to 16.75%.At the same time,the performance of RFI-QKD in terms of the secret key rate and maximum transmission distance are still greatly improved when statistical fluctuations are considered.We conclude that RFI-QKD with the TWCC method is of practical interest.

Phase-matching quantum key distribution with imperfect sources

The huge discrepancies between actual devices and theoretical assumptions severely threaten the security of quantum key distribution.Recently,a general new framework called the reference technique has attracted wide attention in defending against the imperfect sources of quantum key distribution.Here,the state preparation flaws,the side channels of mode dependencies,the Trojan horse attacks,and the pulse classical correlations are studied by using the reference technique on the phase-matching protocol.Our simulation results highlight the importance of the actual secure parameters choice for transmitters,which is necessary to achieve secure communication.Increasing the single actual secure parameter will reduce the secure key rate.However,as long as the parameters are set properly,the secure key rate is still high.Considering the influences of multiple actual secure parameters will significantly reduce the secure key rate.These actual secure parameters must be considered when scientists calibrate transmitters.This work is an important step towards the practical and secure implementation of phase-matching protocol.In the future,it is essential to study the main parameters,find out their maximum and general values,classify the multiple parameters as the same parameter,and give countermeasures.

Th17、IL-17在长程持续性心房颤动中的作用机制

目的探讨外周血中辅助性T细胞17(Th17)及其细胞因子在长程持续性心房颤动(以下简称房颤)中的作用机制。方法回顾性收集2017年1月-2017年12月该院收治的长程持续性房颤患者的临床资料,将该50例作为观察组,选取同期健康成人50例作为对照组。观察两组外周血中Th17及其细胞因子表达水平,并进一步分析长程持续性房颤患者Th17、白介素-17(IL-17)与临床特征的相关性。结果与对照组比较,观察组Th17、IL-17升高(P<0.05)。合并高血压患者的Th17水平高于未合并高血压患者(P<0.05);合并高血压或糖尿病房颤患者的IL-17水平高于未合并患者(P<0.05)。长程持续性房颤患者Th17、IL-17与左室内射血分数呈负相关(r=-0.212和-0.209,P=0.021和0.028)。结论长程持续性房颤患者外周血中Th17、IL-17升高,与高血压、糖尿病和心功能不全有关。

Finite-key analysis of practical time-bin high-dimensional quantum key distribution with afterpulse effect

High-dimensional quantum resources provide the ability to encode several bits of information on a single photon,which can particularly increase the secret key rate rate of quantum key distribution(QKD) systems. Recently, a practical four-dimensional QKD scheme based on time-bin quantum photonic state, only with two single-photon avalanche detectors as measurement setup, has been proven to have a superior performance than the qubit-based one. In this paper, we extend the results to our proposed eight-dimensional scheme. Then, we consider two main practical factors to improve its secret key bound. Concretely, we take the afterpulse effect into account and apply a finite-key analysis with the intensity fluctuations.Our secret bounds give consideration to both the intensity fluctuations and the afterpulse effect for the high-dimensional QKD systems. Numerical simulations show the bound of eight-dimensional QKD scheme is more robust to the intensity fluctuations but more sensitive to the afterpulse effect than the four-dimensional one.

Pulse-gated mode of commercial superconducting nanowire single photon detectors

High detection efficiency and low intrinsic dark count rate are two advantages of superconducting nanowire single photon detectors(SNSPDs).However,the stray photons penetrated into the fiber would cause the extrinsic dark count rate,owing to the free running mode of SNSPDs.In order to improve the performance of SNSPDs in realistic scenarios,stray photons should be investigated and suppression methods should be adopted.In this study,we demonstrate the pulsegated mode,with 500 kHz gating frequency,of a commercial SNSPD system for suppressing the response of stray photons about three orders of magnitude than its free-running counterpart on the extreme test conditions.When we push the gating frequency to 8 MHz,the dark count rate still keeps under 4% of free-running mode.In experiments,the intrinsic dark count rate is also suppressed to 4.56 × 10^(-2) counts per second with system detection efficiency of 76.4372%.Furthermore,the time-correlated single-photon counting analysis also approves the validity of our mode in suppressing the responses of stray photons.

Flexible and Stretchable Electrodes for In Vivo Electrophysiological and Electrochemical Monitoring

In vivo monitoring of bioelectrical and biochemical signals with implanted electrodes has received great interest over the past decades.However,this faces huge challenges because of the severe mechanical mismatch between conventional rigid electrodes and soft biological tissues.In recent years,the emergence of flexible and stretchable electrodes offers seamless and conformable biological-electronic interfaces and has demonstrated significant advantages for in vivo electrochemical and electrophysiological monitoring.This review first summarizes the strategies for electrode fabrication from the point of substrate and conductive materials.Next,recent progress in electrode functionalization for improved performance is presented.Then,the advances of flexible and stretchable electrodes in exploring bioelectrical and biochemical signals are introduced.Finally,we present some challenges and perspectives ranging from electrode fabrication to application.

Security of quantum key distribution with virtual mutually unbiased bases

In a perfect quantum key distribution(QKD)protocol,quantum states should be prepared and measured with mutually unbiased bases(MUBs).However,in a practical QKD system,quantum states are generally prepared and measured with imperfect MUBs using imperfect devices,possibly reducing the secret key rate and transmission distance.To analyze the security of a QKD system with imperfect MUBs,we propose virtual MUBs to characterize the quantum channel against collective attack,and analyze the corresponding secret key rate under imperfect state preparation and measurement conditions.More generally,we apply the advantage distillation method for analyzing the security of QKD with imperfect MUBs,where the error tolerance and transmission distance can be sharply improved.Our analysis method can be applied to benchmark and standardize a practical QKD system,elucidating the security analysis of different QKD protocols with imperfect devices.