Quantum key distribution(QKD)is recognized as an unconditionally secure method of communication encryption,relying solely on the principles of quantum mechanics.A key performance metric for QKD systems is secure key r...Quantum key distribution(QKD)is recognized as an unconditionally secure method of communication encryption,relying solely on the principles of quantum mechanics.A key performance metric for QKD systems is secure key rate(SKR),which is a critical factor for real-world applications.Herein,we report a practical QKD system,equipped with compact gated InGaAs/InP single-photon detectors(SPDs),that can generate a high SKR of 15.2 Mb/s with a channel loss of 2 dB.This exceptional performance stems from the ultra-low afterpulsing probability of the SPDs,which significantly reduces the bit error rate in the QKD system.The typical quantum bit error rate is 1.3%.The results validate the feasibility of an integrated,practical QKD system and offer a reliable solution for the future development of real-world QKD networks.展开更多
Increasing the detection efficiency （DE） is a hot issue in the development of the superconducting nanowire single photon detector （SNSPD）. In this work, a cavity-integrated structure coupled to the SNSPD is used t...Increasing the detection efficiency （DE） is a hot issue in the development of the superconducting nanowire single photon detector （SNSPD）. In this work, a cavity-integrated structure coupled to the SNSPD is used to enhance the light absorption of nanowire. Ultra-thin Nb films are successfully prepared by magnetron sputtering, which are used to fabricate Nb/Al SNSPD with the curve of lOOnm and the square area of 4 × 4μm2 by sputtering and the lift-off method. To characterize the optical and electrical performance of the cavity-integrated SNSPD, a reliable cryogenic research system is built up based on a He3 system. To satisfy the need of light coupling, a packaging structure with collimator is conducted. Both DE and the dark count rates increase with lb. It is also found that the DE of SNSPD with cavities can be up to 0.17% at the temperature of 0.7K under the infrared light of 1550nm, which is obviously higher than that of the SNSPD directly fabricated upon silicon without any cavity structure.展开更多
Quantum key distribution(QKD),rooted in quantum mechanics,offers information-theoretic security.However,practi-cal systems open security threats due to imperfections,notably bright-light blinding attacks targeting sin...Quantum key distribution(QKD),rooted in quantum mechanics,offers information-theoretic security.However,practi-cal systems open security threats due to imperfections,notably bright-light blinding attacks targeting single-photon detectors.Here,we propose a concise,robust defense strategy for protecting single-photon detectors in QKD systems against blinding attacks.Our strategy uses a dual approach:detecting the bias current of the avalanche photodiode(APD)to defend against con-tinuous-wave blinding attacks,and monitoring the avalanche amplitude to protect against pulsed blinding attacks.By integrat-ing these two branches,the proposed solution effectively identifies and mitigates a wide range of bright light injection attempts,significantly enhancing the resilience of QKD systems against various bright-light blinding attacks.This method forti-fies the safeguards of quantum communications and offers a crucial contribution to the field of quantum information security.展开更多
InGaAs/InP avalanche photodiodes （APD） are rarely used in a free-running regime for near-infrared single photon detection. In order to overcome the detrimental afterpulsing, we demonstrate a passive quenching active...InGaAs/InP avalanche photodiodes （APD） are rarely used in a free-running regime for near-infrared single photon detection. In order to overcome the detrimental afterpulsing, we demonstrate a passive quenching active reset integrated circuit. Taking advantage of the inherent fast passive quenching process and active reset to reduce reset time, the integrated circuit is useful for reducing afterpulses and is also area-efficient. We investigate the free-running single photon detector＇s afterpulsing effect, de-trapping time, dark count rate, and photon detection efficiency, and also compare with gated regime operation. After correction for deadtime and afterpulse, we find that the passive quenching active reset free-running single photon detector＇s performance is consistent with gated operation.展开更多
This paper critically analyses and simulates the circuit configuration of the integral gated mode single photon detector which is proposed for eliminating the transient spikes problem of conventional gated mode single...This paper critically analyses and simulates the circuit configuration of the integral gated mode single photon detector which is proposed for eliminating the transient spikes problem of conventional gated mode single photon detector. The relationship between the values of the circuit elements and the effect of transient spikes cancellation has been obtained. With particular emphasis, the bias voltage of the avalanche photodiode and the output signal voltage of the integrator have been calculated. The obtained analysis results indicate that the output signal voltage of the integrator only relates to the total quantity of electricity of the avalanche charges by choosing the correct values of the circuit elements and integral time interval. These results can be used to optimize the performance of single photon detectors and provide guides for the design of single photon detectors.展开更多
Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conven- tional methods adopt sampling gates with fixed width and count the triggered number of sampling...Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conven- tional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation （MVUE） method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.展开更多
The performance of single-photon detectors can be enhanced by using nano-antenna. The characteristics of the superconducting nano-wire single-photon detector with cavity plus anti-reflect coating and specially designe...The performance of single-photon detectors can be enhanced by using nano-antenna. The characteristics of the superconducting nano-wire single-photon detector with cavity plus anti-reflect coating and specially designed nano~ antenna is analysed. The photon collection efficiency of the detector is enhanced without damaging the detector＇s speed, thus getting rid of the dilemma of speed and efficiency. The characteristics of nano-antenna are discussed, such as the position and the effect of the active area, and the best result is given. The photon collection efficiency is increased by 92 times compared with that of existing detectors.展开更多
A newly developed single quad mass spectrometry （MS） detector was coupled to a ultra-high perfor- mance liquid chromatography （UPLC） system and implemented in the routine quality control （QC） and impurity analys...A newly developed single quad mass spectrometry （MS） detector was coupled to a ultra-high perfor- mance liquid chromatography （UPLC） system and implemented in the routine quality control （QC） and impurity analysis of four therapeutic peptides, namely bleomycin sulfate, tyrothricin, vancomycin HCl and bacitracin, which were selected given their multi-component drug nature and their closely struc- turally related impurity profiles. The QC and impurity profiling results obtained using the ultra-high performance liquid chromatography ultraviolet/mass spectrometry （UPLC-UV/MS） detection system were analyzed against the results obtained using traditional high performance liquid chromatography- ultraviolet detection （HPLC-UV） methods derived from pharmacopoeial methods. In general, the used stationary phases of sub-2 μm particle （UPLC） technology resulted in lower limits of detection and higher resolution separations, which resulted in more detected impurities and shorter overall run times con- trasting the traditional HPLC columns. Moreover, online coupling with a single quad MS detector allowed direct peak identification of the main compounds as well as small impurities, hereby increasing the information content without the need of reference standards.展开更多
The superconducting nanowire single photon detector（SNSPD） draws much attention because of its attractive performance at ultra violet, visible, and nearinfrared wavelengths, and it can be widespread in quantum infor...The superconducting nanowire single photon detector（SNSPD） draws much attention because of its attractive performance at ultra violet, visible, and nearinfrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material,it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles,and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with frontillumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed.Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.展开更多
A new method to study the transient detection efficiency （DE） and pulse amplitude of superconducting nanowire single photon detectors （SNSPD） during the current recovery process is proposed -- statistically analyz...A new method to study the transient detection efficiency （DE） and pulse amplitude of superconducting nanowire single photon detectors （SNSPD） during the current recovery process is proposed -- statistically analyzing the single photon response under photon illumination with a high repetition rate. The transient DE results match well with the DEs deduced from the static current dependence of DE combined with the waveform of a single-photon detection event. This proves that static measurement results can be used to analyze the transient current recovery process after a detection event. The results are relevant for understanding the current recovery process of SNSPDs after a detection event and for determining the counting rate of SNSPDs.展开更多
X-ray charge-coupled-device（CCD） camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon countin...X-ray charge-coupled-device（CCD） camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode（model： PI-LCX： 1300） are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 ke V with good energy resolution（E /？E ≈ 100 at60 ke V）. The difference in detection efficiency between two CCD cameras is small（5.6% at 5.89 ke V）, but the difference in fraction of the single pixel event between them is much larger（25% at 8.04 ke V）. The obtained small relative error of detection efficiency（2.4% at 5.89 ke V） makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 ke V–30 ke V.展开更多
Security and safety remain paramount concerns for both governments and individuals worldwide.In today’s context,the frequency of crimes and terrorist attacks is alarmingly increasing,becoming increasingly intolerable...Security and safety remain paramount concerns for both governments and individuals worldwide.In today’s context,the frequency of crimes and terrorist attacks is alarmingly increasing,becoming increasingly intolerable to society.Consequently,there is a pressing need for swift identification of potential threats to preemptively alert law enforcement and security forces,thereby preventing potential attacks or violent incidents.Recent advancements in big data analytics and deep learning have significantly enhanced the capabilities of computer vision in object detection,particularly in identifying firearms.This paper introduces a novel automatic firearm detection surveillance system,utilizing a one-stage detection approach named MARIE(Mechanism for Realtime Identification of Firearms).MARIE incorporates the Single Shot Multibox Detector(SSD)model,which has been specifically optimized to balance the speed-accuracy trade-off critical in firearm detection applications.The SSD model was further refined by integrating MobileNetV2 and InceptionV2 architectures for superior feature extraction capabilities.The experimental results demonstrate that this modified SSD configuration provides highly satisfactory performance,surpassing existing methods trained on the same dataset in terms of the critical speedaccuracy trade-off.Through these innovations,MARIE sets a new standard in surveillance technology,offering a robust solution to enhance public safety effectively.展开更多
On-chip superconducting nanowire single-photon detectors(SNSPDs)are gaining traction in integrated quantum photonics due to their exceptional performance and the elimination of fiber coupling loss.However,off-chip hig...On-chip superconducting nanowire single-photon detectors(SNSPDs)are gaining traction in integrated quantum photonics due to their exceptional performance and the elimination of fiber coupling loss.However,off-chip high-rejection filters are commonly required to remove the intense pump light employed in quantum states generation,thus remaining the obstacle for embedding SNSPDs into quantum photonic circuits.Here,we explore the integration of SNSPDs with passive pump rejection filters,achieved by cascaded silicon Bragg gratings,on a single substrate.Serving as an entanglement receiver chip,the integrated components show a system detection efficiency of 20.1%and a pump rejection ratio of approximately 56 dB.We successfully verify energy-time entangled photon pairs from a microring resonator with raw visibilities of 92.85%±5.95%and 91.91%±7.34%under two nonorthogonal bases,with use of standard fiber wavelength demultiplexers.Our results pave the way for entanglement resource distribution,offering a promising approach toward the construction of large-scale quantum photonic systems.展开更多
The fabrication of high-quality YBa_(2)Cu_(3)O_(7)−δ(YBCO)nanowires has garnered significant attention in the field of high-temperature superconductivity due to their potential applications in quantum communication,d...The fabrication of high-quality YBa_(2)Cu_(3)O_(7)−δ(YBCO)nanowires has garnered significant attention in the field of high-temperature superconductivity due to their potential applications in quantum communication,deep space exploration,and various other fields.Cl_(2)-assisted reactive ion etching(RIE)stands out as a more effective and efficient method for patterning scalable thin films.However,neither RIE nor high-density RIE has achieved superconducting YBCO nanowires with a width smaller than 3μm.Here,we delve into the factors that limit the line width of Cl_(2)-assisted inductively coupled plasma reactive ion etching(ICP-RIE)processing and the method to elimiate them.Our approach involves utilizing Cl_(2)/Ar as etching gas and incorporating a specialized vacuum heating process after etching.Our experimental results demonstrate the successful realization of 10 nm-thick YBCO nanowires with widths as small as 0.15μm,exhibiting excellent performance in terms of their intrinsic superconducting properties.The mechanism is evidenced by X-ray photoelectron spectroscopy(XPS)analysis in comparison of nanowires with and without heating treatment,in which the residual Cl_(2) on the sidewall of nanowires evaporates and oxidizes Cu^(+)back into Cu^(2+)in an unetched state.展开更多
A method of multi-block Single Shot Multi Box Detector(SSD)based on small object detection is proposed to the railway scene of unmanned aerial vehicle surveillance.To address the limitation of small object detection,a...A method of multi-block Single Shot Multi Box Detector(SSD)based on small object detection is proposed to the railway scene of unmanned aerial vehicle surveillance.To address the limitation of small object detection,a multi-block SSD mechanism,which consists of three steps,is designed.First,the original input images are segmented into several overlapped patches.Second,each patch is separately fed into an SSD to detect the objects.Third,the patches are merged together through two stages.In the first stage,the truncated object of the sub-layer detection result is spliced.In the second stage,a sub-layer suppression and filtering algorithm applying the concept of non-maximum suppression is utilized to remove the overlapped boxes of sub-layers.The boxes that are not detected in the main-layer are retained.In addition,no sufficient labeled training samples of railway circumstance are available,thereby hindering the deployment of SSD.A two-stage training strategy leveraging to transfer learning is adopted to solve this issue.The deep learning model is preliminarily trained using labeled data of numerous auxiliaries,and then it is refined using only a few samples of railway scene.A railway spot in China,which is easily damaged by landslides,is investigated as a case study.Experimental results show that the proposed multi-block SSD method produces an overall accuracy of 96.6%and obtains an improvement of up to 9.2%compared with the traditional SSD.展开更多
Occurrence of crimes has been on the constant rise despite the emerging discoveries and advancements in the technological field in the past decade.One of the most tedious tasks is to track a suspect once a crime is co...Occurrence of crimes has been on the constant rise despite the emerging discoveries and advancements in the technological field in the past decade.One of the most tedious tasks is to track a suspect once a crime is committed.As most of the crimes are committed by individuals who have a history of felonies,it is essential for a monitoring system that does not just detect the person’s face who has committed the crime,but also their identity.Hence,a smart criminal detection and identification system that makes use of the OpenCV Deep Neural Network(DNN)model which employs a Single Shot Multibox Detector for detection of face and an auto-encoder model in which the encoder part is used for matching the captured facial images with the criminals has been proposed.After detection and extraction of the face in the image by face cropping,the captured face is then compared with the images in the CriminalDatabase.The comparison is performed by calculating the similarity value between each pair of images that are obtained by using the Cosine Similarity metric.After plotting the values in a graph to find the threshold value,we conclude that the confidence rate of the encoder model is 0.75 and above.展开更多
基金supported by the Innovation Program for Quantum Science and Technology(Grant No.2024ZD0302500)the National Natural Science Foundation of China(Grant No.62250710162)the Beijing Natural Science Foundation(Grant No.Z230005)。
文摘Quantum key distribution(QKD)is recognized as an unconditionally secure method of communication encryption,relying solely on the principles of quantum mechanics.A key performance metric for QKD systems is secure key rate(SKR),which is a critical factor for real-world applications.Herein,we report a practical QKD system,equipped with compact gated InGaAs/InP single-photon detectors(SPDs),that can generate a high SKR of 15.2 Mb/s with a channel loss of 2 dB.This exceptional performance stems from the ultra-low afterpulsing probability of the SPDs,which significantly reduces the bit error rate in the QKD system.The typical quantum bit error rate is 1.3%.The results validate the feasibility of an integrated,practical QKD system and offer a reliable solution for the future development of real-world QKD networks.
基金Supported by the National Basic Research Program of China under Grant No 2011CBA00304the National Natural Science Foundation of China under Grant Nos 60836001 and 61174084the Tsinghua University Initiative Scientific Research Program under Grant No 20131089314
文摘Increasing the detection efficiency （DE） is a hot issue in the development of the superconducting nanowire single photon detector （SNSPD）. In this work, a cavity-integrated structure coupled to the SNSPD is used to enhance the light absorption of nanowire. Ultra-thin Nb films are successfully prepared by magnetron sputtering, which are used to fabricate Nb/Al SNSPD with the curve of lOOnm and the square area of 4 × 4μm2 by sputtering and the lift-off method. To characterize the optical and electrical performance of the cavity-integrated SNSPD, a reliable cryogenic research system is built up based on a He3 system. To satisfy the need of light coupling, a packaging structure with collimator is conducted. Both DE and the dark count rates increase with lb. It is also found that the DE of SNSPD with cavities can be up to 0.17% at the temperature of 0.7K under the infrared light of 1550nm, which is obviously higher than that of the SNSPD directly fabricated upon silicon without any cavity structure.
基金This work was supported by the Major Scientific and Technological Special Project of Anhui Province(202103a13010004)the Major Scientific and Technological Special Project of Hefei City(2021DX007)+1 种基金the Key R&D Plan of Shandong Province(2020CXGC010105)the China Postdoctoral Science Foundation(2021M700315).
文摘Quantum key distribution(QKD),rooted in quantum mechanics,offers information-theoretic security.However,practi-cal systems open security threats due to imperfections,notably bright-light blinding attacks targeting single-photon detectors.Here,we propose a concise,robust defense strategy for protecting single-photon detectors in QKD systems against blinding attacks.Our strategy uses a dual approach:detecting the bias current of the avalanche photodiode(APD)to defend against con-tinuous-wave blinding attacks,and monitoring the avalanche amplitude to protect against pulsed blinding attacks.By integrat-ing these two branches,the proposed solution effectively identifies and mitigates a wide range of bright light injection attempts,significantly enhancing the resilience of QKD systems against various bright-light blinding attacks.This method forti-fies the safeguards of quantum communications and offers a crucial contribution to the field of quantum information security.
基金supported by the National High Technology Research and Development Program of China(Grant No.2013AA122902)the National Key Scientific Instrument and Equipment Development Project of China(Grant No.2013YQ030595)the National Natural Science Foundation of China(Grant Nos.61274024 and 61474123)
文摘InGaAs/InP avalanche photodiodes （APD） are rarely used in a free-running regime for near-infrared single photon detection. In order to overcome the detrimental afterpulsing, we demonstrate a passive quenching active reset integrated circuit. Taking advantage of the inherent fast passive quenching process and active reset to reduce reset time, the integrated circuit is useful for reducing afterpulses and is also area-efficient. We investigate the free-running single photon detector＇s afterpulsing effect, de-trapping time, dark count rate, and photon detection efficiency, and also compare with gated regime operation. After correction for deadtime and afterpulse, we find that the passive quenching active reset free-running single photon detector＇s performance is consistent with gated operation.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No 2007CB307001)Guangdong Key Technologies R&D Program (Grant No 2007B010400009)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No 2001CB309302)
文摘This paper critically analyses and simulates the circuit configuration of the integral gated mode single photon detector which is proposed for eliminating the transient spikes problem of conventional gated mode single photon detector. The relationship between the values of the circuit elements and the effect of transient spikes cancellation has been obtained. With particular emphasis, the bias voltage of the avalanche photodiode and the output signal voltage of the integrator have been calculated. The obtained analysis results indicate that the output signal voltage of the integrator only relates to the total quantity of electricity of the avalanche charges by choosing the correct values of the circuit elements and integral time interval. These results can be used to optimize the performance of single photon detectors and provide guides for the design of single photon detectors.
基金supported by the Fundamental Research Funds for the Central Universities,China(Grant No.AUGA5710056414)the Program for Innovation Research of Science in Harbin Institute of Technology(Grant Nos.PIRS OF HIT A201412 and PIRS OF HIT Q201505)+3 种基金the National Natural Science Foundation of China(Grant No.11675046)the Doctoral Fund of the Ministry of Education of China(Grant No.20122302120003)the Natural Science Foundation of Heilongjiang Province of China(Grant No.A201303)the Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province,China(Grant No.LBH-Q15060)
文摘Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conven- tional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation （MVUE） method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.
基金Project supported by the National Basic Research Program of China(Grant No.2010CB923202)
文摘The performance of single-photon detectors can be enhanced by using nano-antenna. The characteristics of the superconducting nano-wire single-photon detector with cavity plus anti-reflect coating and specially designed nano~ antenna is analysed. The photon collection efficiency of the detector is enhanced without damaging the detector＇s speed, thus getting rid of the dilemma of speed and efficiency. The characteristics of nano-antenna are discussed, such as the position and the effect of the active area, and the best result is given. The photon collection efficiency is increased by 92 times compared with that of existing detectors.
基金funded by PhD grants of‘Institute for the Promotion of Innovation through Science and Technology in Flanders(IWT-Vlaanderen)’(No.101529(MD)and 121512(BG))
文摘A newly developed single quad mass spectrometry （MS） detector was coupled to a ultra-high perfor- mance liquid chromatography （UPLC） system and implemented in the routine quality control （QC） and impurity analysis of four therapeutic peptides, namely bleomycin sulfate, tyrothricin, vancomycin HCl and bacitracin, which were selected given their multi-component drug nature and their closely struc- turally related impurity profiles. The QC and impurity profiling results obtained using the ultra-high performance liquid chromatography ultraviolet/mass spectrometry （UPLC-UV/MS） detection system were analyzed against the results obtained using traditional high performance liquid chromatography- ultraviolet detection （HPLC-UV） methods derived from pharmacopoeial methods. In general, the used stationary phases of sub-2 μm particle （UPLC） technology resulted in lower limits of detection and higher resolution separations, which resulted in more detected impurities and shorter overall run times con- trasting the traditional HPLC columns. Moreover, online coupling with a single quad MS detector allowed direct peak identification of the main compounds as well as small impurities, hereby increasing the information content without the need of reference standards.
基金financially supported by the China State Key Program for Basic Research (No. 2011CBA00304)Tsinghua University Initiative Scientific Research Program (No. 2010Z01010)the National Natural Science Foundation of China (Nos. 61106121 and 61174084)
文摘The superconducting nanowire single photon detector（SNSPD） draws much attention because of its attractive performance at ultra violet, visible, and nearinfrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material,it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles,and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with frontillumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed.Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.
基金Project supported by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04010200)the National Basic Research Program of China(Grant No.2011CBA00202)the National Natural Science Foundation of China(Grant No.61401441)
文摘A new method to study the transient detection efficiency （DE） and pulse amplitude of superconducting nanowire single photon detectors （SNSPD） during the current recovery process is proposed -- statistically analyzing the single photon response under photon illumination with a high repetition rate. The transient DE results match well with the DEs deduced from the static current dependence of DE combined with the waveform of a single-photon detection event. This proves that static measurement results can be used to analyze the transient current recovery process after a detection event. The results are relevant for understanding the current recovery process of SNSPDs after a detection event and for determining the counting rate of SNSPDs.
基金Project supported by the Science Foundation of China Academy of Engineering Physics(Grant Nos.2013A0103003 and 2012B0102008)the National High-Tech Inertial Confinement Fusion Committee of China
文摘X-ray charge-coupled-device（CCD） camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode（model： PI-LCX： 1300） are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 ke V with good energy resolution（E /？E ≈ 100 at60 ke V）. The difference in detection efficiency between two CCD cameras is small（5.6% at 5.89 ke V）, but the difference in fraction of the single pixel event between them is much larger（25% at 8.04 ke V）. The obtained small relative error of detection efficiency（2.4% at 5.89 ke V） makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 ke V–30 ke V.
文摘Security and safety remain paramount concerns for both governments and individuals worldwide.In today’s context,the frequency of crimes and terrorist attacks is alarmingly increasing,becoming increasingly intolerable to society.Consequently,there is a pressing need for swift identification of potential threats to preemptively alert law enforcement and security forces,thereby preventing potential attacks or violent incidents.Recent advancements in big data analytics and deep learning have significantly enhanced the capabilities of computer vision in object detection,particularly in identifying firearms.This paper introduces a novel automatic firearm detection surveillance system,utilizing a one-stage detection approach named MARIE(Mechanism for Realtime Identification of Firearms).MARIE incorporates the Single Shot Multibox Detector(SSD)model,which has been specifically optimized to balance the speed-accuracy trade-off critical in firearm detection applications.The SSD model was further refined by integrating MobileNetV2 and InceptionV2 architectures for superior feature extraction capabilities.The experimental results demonstrate that this modified SSD configuration provides highly satisfactory performance,surpassing existing methods trained on the same dataset in terms of the critical speedaccuracy trade-off.Through these innovations,MARIE sets a new standard in surveillance technology,offering a robust solution to enhance public safety effectively.
基金Innovation Program for Quantum Science and Technology(2023ZD0300100)Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)+1 种基金National Natural Science Foundation of China(61971408,12033007,92365210,U24A20320)Youth Innovation Promotion Association of the Chinese Academy of Sciences(2020241,2021230)。
文摘On-chip superconducting nanowire single-photon detectors(SNSPDs)are gaining traction in integrated quantum photonics due to their exceptional performance and the elimination of fiber coupling loss.However,off-chip high-rejection filters are commonly required to remove the intense pump light employed in quantum states generation,thus remaining the obstacle for embedding SNSPDs into quantum photonic circuits.Here,we explore the integration of SNSPDs with passive pump rejection filters,achieved by cascaded silicon Bragg gratings,on a single substrate.Serving as an entanglement receiver chip,the integrated components show a system detection efficiency of 20.1%and a pump rejection ratio of approximately 56 dB.We successfully verify energy-time entangled photon pairs from a microring resonator with raw visibilities of 92.85%±5.95%and 91.91%±7.34%under two nonorthogonal bases,with use of standard fiber wavelength demultiplexers.Our results pave the way for entanglement resource distribution,offering a promising approach toward the construction of large-scale quantum photonic systems.
基金supported by the National Key Research and Development Program of China(No.2021YFA0718800)the Natural Science Foundation of Sichuan Province(No.2023NSFSC0993)+1 种基金the National Natural Science Foundation of China(Nos.52021001,U22A20132 and 12074056)Sichuan Science and Technology Program(No.2021JDTD0010).
文摘The fabrication of high-quality YBa_(2)Cu_(3)O_(7)−δ(YBCO)nanowires has garnered significant attention in the field of high-temperature superconductivity due to their potential applications in quantum communication,deep space exploration,and various other fields.Cl_(2)-assisted reactive ion etching(RIE)stands out as a more effective and efficient method for patterning scalable thin films.However,neither RIE nor high-density RIE has achieved superconducting YBCO nanowires with a width smaller than 3μm.Here,we delve into the factors that limit the line width of Cl_(2)-assisted inductively coupled plasma reactive ion etching(ICP-RIE)processing and the method to elimiate them.Our approach involves utilizing Cl_(2)/Ar as etching gas and incorporating a specialized vacuum heating process after etching.Our experimental results demonstrate the successful realization of 10 nm-thick YBCO nanowires with widths as small as 0.15μm,exhibiting excellent performance in terms of their intrinsic superconducting properties.The mechanism is evidenced by X-ray photoelectron spectroscopy(XPS)analysis in comparison of nanowires with and without heating treatment,in which the residual Cl_(2) on the sidewall of nanowires evaporates and oxidizes Cu^(+)back into Cu^(2+)in an unetched state.
文摘针对学生注意力分配困难和对学习影响等问题,提出一种基于机器视觉的精准注意力追踪系统。该系统包括图像采集装置和精准的注意力追踪算法。图像采集装置可以获得更清晰的眼部区域图像。瞳孔中心定位算法用轻量级的MobileNet v3替换VGG16(visual geometry group network),采用两级特征融合和中心关键点预测技术,提高了检测速度和准确率。该算法检测速度可达36帧/s,准确率为97.42%。视线追踪算法旨在解决头部偏移的影响,实现对视线的精确追踪。研发了一款面向学龄儿童的阅读认知评价交互软件。该软件利用采集到的视线坐标计算相关眼动指标,再通过心理学理论分析建模来评估学龄儿童的思维认知能力,为心理学和教育学相关领域研究提供了参考和借鉴。
基金supported by Beijing Natural Science Foundation,China(No.4182020)Open Fund of State Laboratory of Information Engineering in Surveying,Mapping and Remote Sensing,Wuhan University,China(No.17E01)Key Laboratory for Health Monitoring and Control of Large Structures,Shijiazhuang,China(No.KLLSHMC1901)。
文摘A method of multi-block Single Shot Multi Box Detector(SSD)based on small object detection is proposed to the railway scene of unmanned aerial vehicle surveillance.To address the limitation of small object detection,a multi-block SSD mechanism,which consists of three steps,is designed.First,the original input images are segmented into several overlapped patches.Second,each patch is separately fed into an SSD to detect the objects.Third,the patches are merged together through two stages.In the first stage,the truncated object of the sub-layer detection result is spliced.In the second stage,a sub-layer suppression and filtering algorithm applying the concept of non-maximum suppression is utilized to remove the overlapped boxes of sub-layers.The boxes that are not detected in the main-layer are retained.In addition,no sufficient labeled training samples of railway circumstance are available,thereby hindering the deployment of SSD.A two-stage training strategy leveraging to transfer learning is adopted to solve this issue.The deep learning model is preliminarily trained using labeled data of numerous auxiliaries,and then it is refined using only a few samples of railway scene.A railway spot in China,which is easily damaged by landslides,is investigated as a case study.Experimental results show that the proposed multi-block SSD method produces an overall accuracy of 96.6%and obtains an improvement of up to 9.2%compared with the traditional SSD.
文摘Occurrence of crimes has been on the constant rise despite the emerging discoveries and advancements in the technological field in the past decade.One of the most tedious tasks is to track a suspect once a crime is committed.As most of the crimes are committed by individuals who have a history of felonies,it is essential for a monitoring system that does not just detect the person’s face who has committed the crime,but also their identity.Hence,a smart criminal detection and identification system that makes use of the OpenCV Deep Neural Network(DNN)model which employs a Single Shot Multibox Detector for detection of face and an auto-encoder model in which the encoder part is used for matching the captured facial images with the criminals has been proposed.After detection and extraction of the face in the image by face cropping,the captured face is then compared with the images in the CriminalDatabase.The comparison is performed by calculating the similarity value between each pair of images that are obtained by using the Cosine Similarity metric.After plotting the values in a graph to find the threshold value,we conclude that the confidence rate of the encoder model is 0.75 and above.
