In quantum key distribution（QKD）, the times of arrival of single photons are important for the keys extraction and time synchronization. The time-of-arrival（TOA） accuracy can affect the quantum bit error rate（QBE...In quantum key distribution（QKD）, the times of arrival of single photons are important for the keys extraction and time synchronization. The time-of-arrival（TOA） accuracy can affect the quantum bit error rate（QBER） and the final key rate. To achieve a higher accuracy and a better QKD performance, different from designing more complicated hardware circuits, we present a scheme that uses the mean TOA of M frequency-entangled photons to replace the TOA of a single photon. Moreover, to address the problem that the entanglement property is usually sensitive to the photon loss in practice,we further propose two schemes, which adopt partially entangled photons and grouping-entangled photons, respectively.In addition, we compare the effects of these three alternative schemes on the QKD performance and discuss the selection strategy for the optimal scheme in detail. The simulation results show that the proposed schemes can improve the QKD performance compared to the conventional single-photon scheme obviously, which demonstrate the effectiveness of the proposed schemes.展开更多
为识别铝合金板孔损伤位置及区域,以Lamb波为研究基础,提出基于魏格纳-威利分布(WVD,WignerVille distribution)和到达时间差值法(ATDM,arrival time difference method)的损伤识别技术。首先,采集实验铝合金板健康和有损模型的Lamb信号...为识别铝合金板孔损伤位置及区域,以Lamb波为研究基础,提出基于魏格纳-威利分布(WVD,WignerVille distribution)和到达时间差值法(ATDM,arrival time difference method)的损伤识别技术。首先,采集实验铝合金板健康和有损模型的Lamb信号,对其差值信号进行WVD分析,准确提取损伤反射信号到达时间;其次,通过ATDM建立各传感器间的距离差值关系,确定孔损伤位置中心并预测最大损伤半径,从而实现对孔损伤关键指标的识别;最后,通过数值模拟进一步验证该方法,结果表明,基于WVD/ATDM的损伤识别技术不仅能准确识别出孔损伤位置,而且能够有效地识别损伤区域面积。展开更多
Optimal Models for first arrival time (rH) and first arrival target total return (WH) distribution functions on MDP in continuous time are presented. Asymptotic expansions of rH and WH are derived and expressed in sim...Optimal Models for first arrival time (rH) and first arrival target total return (WH) distribution functions on MDP in continuous time are presented. Asymptotic expansions of rH and WH are derived and expressed in simple, explicit forms, and some of their properties are discussed. Two methods to find an optimal policy for distribution function of rH are given. Several necessary and sufficient conditions for the existence of the optimal policy are obtained. This result leads to that the scope of finding the optimal policy is greatly reduced. A special case is also discussed and some deep results are given.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61573059,61401340,and 61172138)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2016JM6035)the Fundamental Research Funds for the Central Universities,China(Grant No.JB161303)
文摘In quantum key distribution（QKD）, the times of arrival of single photons are important for the keys extraction and time synchronization. The time-of-arrival（TOA） accuracy can affect the quantum bit error rate（QBER） and the final key rate. To achieve a higher accuracy and a better QKD performance, different from designing more complicated hardware circuits, we present a scheme that uses the mean TOA of M frequency-entangled photons to replace the TOA of a single photon. Moreover, to address the problem that the entanglement property is usually sensitive to the photon loss in practice,we further propose two schemes, which adopt partially entangled photons and grouping-entangled photons, respectively.In addition, we compare the effects of these three alternative schemes on the QKD performance and discuss the selection strategy for the optimal scheme in detail. The simulation results show that the proposed schemes can improve the QKD performance compared to the conventional single-photon scheme obviously, which demonstrate the effectiveness of the proposed schemes.
文摘为识别铝合金板孔损伤位置及区域,以Lamb波为研究基础,提出基于魏格纳-威利分布(WVD,WignerVille distribution)和到达时间差值法(ATDM,arrival time difference method)的损伤识别技术。首先,采集实验铝合金板健康和有损模型的Lamb信号,对其差值信号进行WVD分析,准确提取损伤反射信号到达时间;其次,通过ATDM建立各传感器间的距离差值关系,确定孔损伤位置中心并预测最大损伤半径,从而实现对孔损伤关键指标的识别;最后,通过数值模拟进一步验证该方法,结果表明,基于WVD/ATDM的损伤识别技术不仅能准确识别出孔损伤位置,而且能够有效地识别损伤区域面积。
文摘Optimal Models for first arrival time (rH) and first arrival target total return (WH) distribution functions on MDP in continuous time are presented. Asymptotic expansions of rH and WH are derived and expressed in simple, explicit forms, and some of their properties are discussed. Two methods to find an optimal policy for distribution function of rH are given. Several necessary and sufficient conditions for the existence of the optimal policy are obtained. This result leads to that the scope of finding the optimal policy is greatly reduced. A special case is also discussed and some deep results are given.
