Countermeasure against blinding attack for single-photon detectors in quantum key distribution

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.

Superconducting Nanowire Single Photon Detector with Optical Cavity

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.

Detection efficiency characteristics of free-running InGaAs/InP single photon detector using passive quenching active reset IC

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.

The analysis of the integral gated mode single photon detector

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.

The intensity detection of single-photon detectors based on photon counting probability density statistics

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.

Performance of a superconducting single photon detector with nano-antenna

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.

Controlling a sine wave gating single-photon detector by exploiting its filtering loophole

GHz single-photon detector （SPD） is a crucial part in the practical high speed quantum key distribution （QKD） system. However, any imperfections in a practical QKD system may be exploited by an eavesdropper （Eve） to collect information about the key without being discovered. The sine wave gating SPD （SG-SPD） based on InGaAs/InP avalanche photodiode, one kind of practical high speed SPD, may also contain loopholes. In this paper, we study the principle and characteristic of the SG-SPD and find out the filtering loophole of the SG-SPD for the first time. What is more, the proof-of-principle experiment shows that Eve could blind and control Bob＇s SG-SPD by exploiting this loophole. We believe that giving enough attention to this loophole can improve the practical security of the existing QKD system. GHz single-photon detector （SPD） is a crucial part in the practical high speed quantum key distribution （QKD） system. However, any imperfections in a practical QKD system may be exploited by an eavesdropper （Eve） to collect information about the key without being discovered. The sine wave gating SPD （SG-SPD） based on InGaAs/InP avalanche photodiode, one kind of practical high speed SPD, may also contain loopholes. In this paper, we study the principle and characteristic of the SG-SPD and find out the filtering loophole of the SG-SPD for the first time. What is more, the proof-of-principle experiment shows that Eve could blind and control Bob＇s SG-SPD by exploiting this loophole. We believe that giving enough attention to this loophole can improve the practical security of the existing QKD system.

Performance of superconducting nanowire single-photon detector with the fan coupling antenna array

The performance of superconducting nanowire single-photon detector （SNSPD） involving niobium nitride with the fan coupling antenna array is analyzed. The SNSPD has a high detection efficiency and counting rate. Hydrogen silsesquioxane and niobium nitride are filled in the gold grating deposited on the substrate in which the fan coupling antenna arrays are embedded. By changing the position of the fan coupling antenna array, the maximum area of optical intensity is obtained and the photon collection efficiency is increased by 26.5 times. The detection efficiency of SNSPD is improved without changing the detection speed. These parameters are important for designing a practical single-photon detector,

Resonant cavity-enhanced quantum dot field-effect transistor as a single-photon detector

A resonant cavity-enhanced （RCE） quantum dot （QD） field-effect transistor （RCEQDFET） is designed for single- photon detection in this paper. Adding distributed Bragg reflection （DBR） mirrors to the single-photon detector （SPD）, we improve the light absorption efficiency of the SPD. The effects of the reflectivity of the mirrors, the thickness and light absorption coefficient of the absorbing layer on the detector＇s light absorption efficiency are investigated, and the resonant cavity is determined by using the air/semiconductor interface as the mirror on the top. Through analyzing the relationship between the refractive index of AlxGal_xAs and A1 component, we choose A1As/Alo.15Gao.85As as the material of the mirror on the bottom. The pairs of A1As/Alo.15Gao.85As film are further determined to be 21 by calculating the reflectivity of the mirror. The detector is fabricated from semiconductor heterostructures grown by molecular beam epitaxy. The reflection spectrum, photoluminescence （PL） spectrum, photocurrent response, and channel current of the detector are tested and the results show that the RCEQDFET-SPD designed in this paper has better performances in photonic response and wavelength selection.

High-performance eight-channel system with fractal superconducting nanowire single-photon detectors

Superconducting nanowire single-photon detectors(SNSPDs)have become a mainstream photon-counting technology that has been widely applied in various scenarios.So far,most multi-channel SNSPD systems,either reported in literature or commercially available,are polarization sensitive,that is,the system detection efficiency(SDE)of each channel is dependent on the state of polarization of the to-be-detected photons.Here,we reported an eight-channel system with fractal SNSPDs working in the wavelength range of 930 to 940 nm,which are all featured with low polarization sensitivity.In a close-cycled Gifford-McMahon cryocooler system with the base temperature of 2.2 K,we installed and compared the performance of two types of devices:(1)SNSPD,composed of a single,continuous nanowire and(2)superconducting nanowire avalanche photodetector(SNAP),composed of 16 cascaded units of two nanowires electrically connected in parallel.The highest SDE among the eight channels reaches 96+^(4)_(-5%),with the polarization sensitivity of 1.02 and a dark-count rate of 13 counts per second.The average SDE for eight channels for all states of polarization is estimated to be 90±5%.It is concluded that both the SNSPDs and the SNAPs can reach saturated,high SDE at the wavelength of interest,and the SNSPDs show lower dark-count(false-count)rates,whereas the SNAPs show better properties in the time domain.With the adoption of this system,we showcased the measurements of the second-order photon-correlation functions of light emission from a singlephoton source based on a semiconductor quantum dot and from a pulsed laser.It is believed that this work will provide new choices of systems with single-photon detectors combining the merits of high SDE,low polarization sensitivity,and low noise that can be tailored for different applications.

Wavelength dependence of intrinsic detection efficiency of NbN superconducting nanowire single-photon detector

Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.In this study, we investigate the wavelength dependence of the intrinsic detection efficiency(IDE) for NbN SNSPDs.We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm.Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained.From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted.The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs.Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.

Quest towards ultimate performance in superconducting nanowire single photon detectors

In 2007, superconducting nanowire single photon detectors （SSPD or SNSPD） [ 1 ] made an outstanding impact in the field of quantum information technology by demonstrating quan- tum key distribution （QKD） over a 200-kin optical fiber with a 42-dB optical loss using a practical SNSPD system [2]. This successful demonstration was realized thanks to its extremely low dark count rate （DCR） of a few Hz and short timing jitter of 60 ps, while the system detection efficiency （SDE） showed a poor value of 0.7% at a wavelength of 1550 nm.

Spatial resolution optimization in a THGEM-based UV photon detector

Introduction THick Gas Electron Multiplier(THGEM)is considered in many UV photon detector applications.It has the capability of detecting single photon and imaging with high sensitivity.Operating parameters such as choice of gas mixture,pressure,drift field,drift gap,multiplication voltage,induction field and induction gap play an important role in deciding the spatial resolution of the detector.Detailed simulation study enables to optimize the above-mentioned parameters for a given THGEM-based imaging detector and hence to achieve improved performance for the same.Materials and methods Simulation,using ANSYS and Garfield++,starts with the release of primary electrons at random coordinates on the photocathode plane.They are tracked as they pass through the drift gap and THGEM hole till the electron cloud reaches anode plane.Distribution of electron cloud on the anode plane along X and Y axis is plotted in histogram and fitted with Gaussian function to determine spatial resolution.Ar/CO_(2)(70:30)mixture,which shows higher ETE and lower transverse diffusion,is chosen for this simulation study.Conclusion Transverse diffusion has a major impact on both ETE and the spatial resolution.Lower transverse diffusion coefficient is always desired for having better resolution as well as for ETE.It is found from the simulation study that higher gas pressure,lower drift field and induction field,smaller drift and induction gap can provide optimum detection efficiency with the best spatial resolution.The simulation method proposed here can also be extended to X-ray imaging detectors.

Single photon response of superconducting nanowire single photon detector

Single photon detection is one of the key technologies for quantum key distribution in quantum communication. As a novel single photon detection technology, superconducting nanowire single photon detector (SNSPD) surpasses conventional semiconducting single photon detectors with high count rate and low dark count rate. In this article, we introduce SNSPD fabricated from NbN ultrathin superconducting film and lab-based SNSPD system. The characteristics of single photon response pulse of SNSPD are analyzed in detail. Also discussed is the relationship between waveform of single photon response and system bandwidth. Circuit model is made to analyze the performance of SNSPD. The simulation result agrees well with the experimental data. Those results are valuable for understanding the mechanism of SNSPD and building future SNSPD system for quantum communication.

Improve the Efficiency of Scintillation Detectors Using Reflectors Based on Photonic Crystals Arrays

In the present work, we designed the new type of photonic crystals (PCs) as reflectors. Reflections from single layer of Al2O3/MgO PC help us in recapturing the light that does escape from the scintillation surface. Photonic crystals in one dimension array of Al2O3 and MgO with silver at periodicities N = 1, 2 and 3 were used as a reflector around the surface of the scintillation volume. Scintillation detectors are widely used in nuclear medicine. The efficiency is an important parameter for characterizing the capability of the detectors. The counting efficiency of the detectors depends on the light emission induced by radiation. The light then was converted by the photomultiplier tube into electrical pulses. The efficiency may increase by an amount of 1.64% if MgO-Ag photonic crystals are used at periodicity N = 1 as a reflector.

Estimation of photon counting statistics with imperfect detectors

The study on photon counting statistics is of fundamental importance in quantum optics. We theoretically analyzed the imperfect detection of an arbitrary quantum state. We derived photon counting formulae for six typical quantum states （i.e., Fock, coherent, squeeze-vacuum, thermal, odd and even coherent states） with finite quantum efficiencies and dark counts based on multiple on/off detector arrays. We applied the formulae to the simulation of multiphoton number detections and obtained both the simulated and ideal photon number distributions of each state. A comparison between the results by using the fidelity and relative entropy was carried out to evaluate the detection scheme and help select detectors for different quantum states.

Passive decoy state SARG04 quantum-key-distribution with practical photon-number resolving detectors

SARG04 protocol has its advantages in defending photon number splitting attack, benefited from two-photon pulses part. In this paper, we present a passive decoy state SARG04 scheme combining with practical photon number resolving （PNR） detectors. Two kinds of practical detectors, transition-edge sensor and time-multiplexing detector, are taken into consideration. Theoretical analysis shows that both of them are compatible with the passive decoy state SARG04. Compared with the original SARG04, two detectors can boost the key generation rate and maximal secure distance obviously. Meanwhile, the result shows that quantum efficiency and dark count of the detector influence the maximal distance slightly, which indicates the prospect of implementation in real quantum key distribution system with imperfect practical PNS detectors.

An FPGA-Based Pulse Pile-up Rejection Technique for Photon Counting Imaging Detectors

A novel FPGA-based pulse pile-up rejection method for single photon imaging detectors is reported. Tile method is easy to implement in FPGAs for real-time data processing. The rejection principle and entire design are introduced in detail. The photon counting imaging detector comprises a micro-channel plate （MCP） stack, and a wedge and strip anode （WSA）. The resolution mask pattern in front of the MCP can be reconstructed after data processing in the FPGA. For high count rates, the rejection design can effectively reduce the impact of the pulse pile-up on the image. The resolution can reach up to 140μm. The pulse pile-up rejection design can also be applied to high-energy physics and particle detection.

X-ray photon counting detectors for preclinical and clinical applications

Photon counting detectors(PCDs) have attained w ide use in X-ray imaging for various preclinical and clinical applications in the past decade. This paper briefly review s the preclinical and clinical applications of PCDs based X-ray imaging systems.Starting with an introduction of X-ray single photon detection mechanism,the brief review first describes tw o major advantages of utilizing PCDs: photon energy resolving capability and electronic noise elimination. Compared to energy integrating detectors(EIDs),the aforementioned advantages make PCDs more favorable in X-ray imaging with profound benefits such as enhanced tissue contrast,decreased image noise,increased signal to noise ratio,decreased radiation dose to the small animals and patients,and more accurate material decomposition. The utilizations of PCDs in X-ray projection radiography and computed tomography(CT)including micro-CT,dedicated breast CT,K-edge CT,and clinical CT are then review ed for the imaging applications ranging from phantoms to small animals and humans. In addition,optimization methods aiming to improve the imaging performance using PCDs are briefly review ed. PCDs are not flaw less though,and their limitations are also discussed in this review. Nevertheless,PCDs may continuously contribute to the advancement of X-ray imaging techniques in future preclinical and clinical applications.

感应读出延时线阳极光子计数探测器研究

针对空间天文、生物荧光、光谱测量等领域对高灵敏、大面阵探测器的应用需求,研制出基于感应读出方式的延迟线阳极光子计数成像探测器。该探测器由微通道板、延时线阳极以及读出电路组成,其中延时线阳极的性能直接影响探测器的成像质量。作为一种电荷感应读出延时线阳极,该阳极利用信号到达的时间差解码入射光子的位置,可获得高的探测灵敏度和大的成像面积,同时简化了工艺难度并提升了可靠性。设计了感应读出延时线阳极,理论分析了探测器不同设计参数及材料对感应电荷量的影响,提出了解决异层电极间感应电荷量难以平衡的方法。据此研制出了收集面积为40 mm×40 mm的位敏阳极。测试结果表明该阳极信号传输衰减小于10%,极间串扰小于3%。利用该阳极进行了光子计数成像实验,获得了优于150μm的空间分辨率,为研制可应用于天文紫外光谱测量的大面阵、高灵敏探测器提供了理论依据及实验指导。