超导纳米线单光子探测器件的制备

超导纳米线单光子探测器件(SNSPD)是超导单光子探测系统的核心器件。文中介绍了成功制备的基于5nm厚的NbN超导超薄薄膜的SNSPD器件。器件核心结构为150nm宽的纳米曲折线结构,纳米线条占空比为75%,面积为20μm×20μm。超导纳米线是利用电子束曝光(EBL)技术和反应离子刻蚀(RIE)等工艺技术制备的。所制备的SNSPD样品,在温度3.5K下的临界电流约12.9μA;在1310nm波长光波辐照,12.5μA的偏置电流下,探测效率约0.016%。     

超导单光子探测器件直流特性研究

超导单光子探测技术是基于超薄超导薄膜的非平衡态热电子效应的一种新型的单光子探测方法。超导单光子探测器(SNSPD)的计数率可达到GHz,时间抖动小于100ps,因而在未来量子通信系统中有着广阔的应用前景。介绍了NbN超导单光子探测器件的工作原理和器件超导性能测试系统;测试了超导单光子探测器件的电阻-温度、电流-电压等特性。并对测试结果进行了分析和讨论。     

面向窄线宽超导纳米线单光子探测器的电子束曝光技术

超导纳米线单光子探测器是新型超导电子器件,因其具有高探测效率、低暗计数及低时间抖动等优势,在量子信息、激光雷达等方面已得到广泛的应用.目前主流超导纳米线单光子探测器主要工作在1.5μm以下的可见光和近红外波段.中红外波长的红外探测技术在基础科学、医学、日常生活以及军事等广泛领域发挥着重要作用,中红外单光子探测器可以使得中红外波段探测技术进入量子极限灵敏度.根据超导纳米线单光子探测器探测机理,超窄线宽的纳米线条可以提升超导纳米线单光子探测器在中红外波长的灵敏度.电子束曝光技术是目前实现超导纳米线单光子探测器纳米线线条加工的主流技术,电子束抗蚀剂种类繁多,面向超窄线宽超导纳米线单光子探测器器件的制备需求,对两款抗蚀剂进行性能测试表征,和窄纳米线制备尝试.根据负性电子束抗蚀剂MaN-2401在制备窄线宽时的显著优点,优化工艺,利用其成功制备出50 nm线宽超导纳米线单光子探测器并成功实现了2000 nm的单光子响应.     

基于电热模型的SNSPD响应过程模拟与时间抖动分析

超导单光子探测器(SNSPD)具有高探测效率,低时间抖动、低暗计数率、高计数率等优点.文章通过对纳米线电热过程的建模,分析了纳米线的电热响应过程,探讨了负载电阻、偏置电流和动态电感对SNSPD响应时间的影响,结合蒙特卡洛方法来模拟研究了纳米线空间不均匀性对于SNSPD时间抖动的影响,结果表明随着纳米线空间不均匀性的增加,纳米线的时间抖动不断增加,并求出了典型的时间抖动约为7.73 ps.     

氮化铌纳米线光学特性

氮化铌(NbN)纳米线是超导纳米线单光子探测器(SNSPD)常用的光敏材料,其光学性质是影响SNSPD性能的关键因素.本文结合实验数据和仿真结果,系统研究了多种NbN超导纳米线探测器器件结构的光学特性,表征了以下四种器件结构下的反射光谱以及透射光谱:1)双面热氧化硅衬底背面对光结构;2)双面SiN硅衬底背面对光结构;3)硅衬底上以金层+SiN缓冲层为反射镜的正面对光结构;4)以分布式布拉格反射镜(DBR)为衬底的正面对光结构.并在上述四种器件结构基础上,生长了不同厚度的NbN薄膜,观察不同厚度NbN薄膜的吸收效率.经分析,发现在不同器件结构下的最佳NbN厚度与光吸收率的关系如下:双面热氧化硅衬底上的NbN层在1606 nm处最大吸收率为91.7%,其余结构在最佳NbN厚度条件下吸收率都能达到99%以上.其中双面SiN的硅衬底结构中最大吸收率为99.3%, Au+SiN为99.8%, DBR为99.9%.最后,将DBR器件实测结果与仿真结果进行了差异性分析.这些结果对高效率SNSPD设计与研制具有指导意义.     

Single photon detectors based on superconducting nanowires over?large active areas

Single photon detectors based on superconducting niobium nitride (NbN) nanowires over areas of 30 μm×30 μm are fabricated using E-beam lithography (EBL) and reactive ion etching (RIE). SEM images of the NbN nanowires indicate that the widths are uniformly 200 nm over the whole lengths and the fill factors are about 66.7%. The detectors are characterized at optical wavelengths of 810, 1310 and 1550 nm, respectively. Maximum detector efficiencies (DE) of 0.3% at 1550 nm and 0.6% at 1310 nm are obtained, and the resetting times are just about 10 ns. Additionally we demonstrated the broadband response properties of the devices as well as linear relations between the count rates and incident photon numbers.     

单光子探测技术

近年来,以量子密钥分配为代表的各种量子信息技术应用获得了飞速发展,这些应用对单光子探测器的性能提出了非常苛刻的要求,以光电倍增管和雪崩光电二极管为代表的传统单光子探测器件已经无法满足需求。在此背景下,出现了以超导单光子探测器为代表的新型低温单光子探测器件,其性能比现有商用单光子探测器有了本质性的提升。本文综述了迄今为止各种类型的单光子探测器,并指出各自在量子信息技术应用中的优势和不足之处以及发展方向。     

NbN superconducting nanowire single photon detector with efficiency over 90% at 1550 nm wavelength operational at compact cryocooler temperature

The rapid development of superconducting nanowire single-photon detectors over the past decade has led to numerous advances in quantum information technology. The record for the best system detection efficiency at an incident photon wavelength of 1550 nm is 93%. This performance was attained from a superconducting nanowire single-photon detector made of amorphous WSi; such detectors are usually operated at sub-Kelvin temperatures. In this study, we first demonstrate superconducting nanowire single-photon detectors made of polycrystalline NbN with system detection efficiency of 90.2% for 1550-nm-wavelength photons at 2.1 K, accessible with a compact cryocooler. The system detection efficiency saturated at 92.1% when the temperature was lowered to 1.8 K. We expect the results lighten the practical and high performance superconducting nanowire single-photon detectors to quantum information and other high-end applications.     

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,     

基于超导纳米线单光子探测器深空激光通信模型及误码率研究

高速深空通信是深空探测的关键技术之一,具备单光子灵敏度的激光通信系统将大大提高现有的深空通信速度.然而,单光子条件下的激光通信不仅需要考虑传输环境的影响,还需要考虑实际单光子探测器性能和光子数量子态的分布.本文在不考虑大气湍流影响的情况下,以光电探测模型为基础,引入超导纳米线单光子探测器(SNSPD)系统的探测效率和暗计数,建立了反应系统差错性能的数学模型,提出了系统误码率的计算公式.先对公式中的光强和激光脉冲重复频率对误码率的影响进行仿真,再通过实验结果验证仿真模型.结果表明,光强对误码率的影响最明显,随着光强从0.01光子/脉冲到1000光子/脉冲的增加,误码率从10~(-1)到10~(-7)量级明显下降;激光脉冲重复频率对误码率的影响受到不同光强的制约,但都随着脉冲重复频率的增加呈下降趋势.与此同时,当增加光强或者提高速度时,误码率高于仿真结果,约在10~(-4)量级,其原因可能是实际通信中调制光信号的消光比不足和光纤引入背景噪声提高了系统暗计数.以上模型和实验结果为进一步开展基于SNSPD的月球-地球、火星-地球等高速深空激光通信奠定了基础.     

Doped niobium superconducting nanowire single-photon detectors

We designed and fabricated a special doped niobium (Nb*) superconducting nanowire single-photon detector (SNSPD) on MgO substrate. The superconductivity of this ultra-thin Nb* film was further improved by depositing an ultra-thin aluminum nitride protective layer on top. Compared with traditional Nb films, Nb* films present higher T _C and J _C. We investigated the dependence of the characteristics of devices, such as cut-off wavelength, response bandwidth, and temperature, on their geometrical dimensions. Results indicate that reduction in both the width and thickness of Nb* nanowires extended the cut-off wavelength and improved the sensitivity. The Nb* SNSPD (50 nm width and 4.5 nm thickness) exhibited single-photon sensitivities at 1,310, 1,550, and 2,010 nm. We also demonstrated an enhancement in the detection efficiency by a factor of 10 in its count rate by lowering the working temperature from 2.26 K to 315 mK.     

低维超导的实验进展

超导自发现以来, 已成为凝聚态物理领域最重要的方向之一. 近年来, 低维材料制备技术的进步使得一维或二维的超导特性实验研究成为可能. 本文在简要介绍超导现象的基础上, 重点回顾了近些年二维超导薄膜和一维超导纳米线的制备和电输运研究, 以及在低维超导体中发现的相移、近邻效应、铁磁超导相互作用和高温超导等新奇的现象, 并对该领域的进一步发展做出了展望.     

Photon-counting chirped amplitude modulation lidar system using superconducting nanowire single-photon detector at 1550-nm wavelength

We demonstrate a photon-counting chirped amplitude modulation(CAM) light detection and ranging(lidar) system incorporating a superconducting nanowire single-photon detector(SNSPD) and operated at a wavelength of 1550 nm.The distance accuracy of the lidar system was determined by the CAM bandwidth and signal-to-noise ratio(SNR) of an intermediate frequency(IF) signal. Owing to a short dead time(10 ns) and negligible dark count rate(70 Hz) of the SNSPD, the obtained IF signal attained an SNR of 42 d B and the direct distance accuracy was improved to 3 mm when the modulation bandwidth of the CAM signal was 240 MHz and the modulation period was 1 ms.     

Intrinsic timing jitter of superconducting nanowire single-photon detectors

We report on an experimental investigation of the timing jitter (TJ) in a fiber-coupled detection system based on a superconducting nanowire single-photon detector (SNSPD). We used a picosecond pulsed laser and fiber delay lines to generate subsequent optical pulsed pairs in each period and measured the TJ between the pulses. Because only the interval time between two pulses in each period was interested, we did not need to know the absolute time of every pulse. Therefore, the TJ from laser and trigger signal can be removed. In order to estimate the intrinsic TJ of SNSPD, we analyzed the TJ caused by time distribution of optical pulse, electronic components, readout noise, kinetic inductance and dispersion in fiber channel. Finally, we obtained the intrinsic TJs for two kinds of detectors considering these impacts.     

超导纳米线单光子探测器

利用磁控溅射、电子束光刻和反应离子刻蚀等微加工技术,开展了超导纳米线单光子探测器(SNSPD)的研究.通过对SNSPD的设计和制备工艺参数的优化,成功制备出了高质量的SNSPD.单光子检测实验表明,制备的SNSPD对660 nm波长的光信号,系统检测效率可达30%,对1550 nm波长光信号,最大系统检测效率为4.2%.在平均暗计数小于10 c/s的情况下,系统检测效率大于20%(660 nm)和3%(1550 nm). 关键词： 单光子 氮化铌 纳米线 探测器     

Photon number resolvability of multi-pixel superconducting nanowire single photon detectors using a single flux quantum circuit

Superconducting nanowire single-photon detectors (SNSPDs) are typical switching devices capable of detecting single photons with almost 100% detection efficiency. However, they cannot determine the exact number of incident photons during a detection event. Multi-pixel SNSPDs employing multiple read-out channels can provide photon number resolvability (PNR), but they require increased cooling power and costly multi-channel electronic systems. In this work, a single-flux quantum (SFQ) circuit is employed, and PNR based on multi-pixel SNSPDs is successfully demonstrated. A multi-input magnetically coupled DC/SFQ converter (MMD2Q) circuit with a mutual inductance M is used to combine and record signals from a multi-pixel SNSPD device. The designed circuit is capable of discriminating the amplitude of the combined signals in accuracy of Φ₀/M with Φ₀ being a single magnetic flux quantum. By employing the MMD2Q circuit, the discrimination of up to 40 photons can be simulated. A 4-parallel-input MMD2Q circuit is fabricated, and a PNR of 3 is successfully demonstrated for an SNSPD array with one channel reserved for the functional verification. The results confirm that an MMD2Q circuit is an effective tool for implementing PNR with multi-pixel SNSPDs.     

高临界电流密度NbN约瑟夫森结的制备和特性表征

我们开展了高临界电流密度的NbN约瑟夫森结的制备和特性研究.利用直流磁控溅射方法在单晶MgO(100)衬底上外延生长NbN/AlN/NbN三层膜,并使用微加工工艺制备了NbN约瑟夫森隧道结,在液氦温度下对NbN约瑟夫森结的电流-电压特性进行了测量,实验结果表明,NbN约瑟夫森结具有良好的隧穿特性,其临界电流密度J_c为10 kA/cm^2,质量因子大于10,能隙是5.7 mV,这些实验结果为基于NbN结的超导数字电路研究奠定了坚实的基础.     

超导纳米线单光子探测器动态电感研究

单光子探测是一种量子极限光信号的检测技术,超导纳米线单光子探测器(Superconducting NanowireSingle-Photon Detector,SNSPD)作为一种新型的单光子探测技术,在量子通信等众多领域有着广阔的应用前景。SNSPD的动态电感直接决定了SNSPD的工作速度。文中对SNSPD动态电感的特性和测试方法做了详细的研究,成功实现了低温下SNSPD动态电感的测试,并对结果进行了分析处理和研究。利用BCS理论对动态电感随温度、偏置电流变化的特性进行分析计算,并与实际测量结果对比讨论,为未来如何降低SNSPD动态电感、提高其性能的研究工作提供了参考依据。     

基于微芯片的透射电子显微镜的低温纳米精度电子束刻蚀与原位电学输运性质测量

利用微芯片制备技术制备了带有电极的原位电学薄膜芯片,并结合自制的原位透射电镜样品台,实现了低温下透射电子显微镜聚焦电子束对InAs纳米线的精细刻蚀以及不同温度下的原位电学性能测量.研究发现,随着刻蚀区域截面积的减小,纳米线的电导率也随之减小.当纳米线的截面积从大于10000 nm2刻蚀至约800 nm2时,纳米线电导的减小速率与截面积的减小具有线性关系.同时利用低温聚焦电子束刻蚀,在InAs纳米线上原位制备了一个10 nm的纳米点,并在77与300 K下对该纳米点进行了电学性能测量.通过测量发现在77 K时出现库仑阻塞效应,发生了电子隧穿现象;而300 K时,热扰动提供的能量使这种现象消失.     

超导转变边沿单光子探测器原理与研究进展

量子信息技术近十多年来的快速发展对单光子探测器的性能提出了更高的要求,高性能单光子探测器也因此受到了更多的关注.与传统的单光子探测器相比,超导转变边沿(TES)单光子探测器在探测效率、能量分辨、光子数分辨和暗计数等方面具有突出优势.目前,超导TES单光子探测器已经被成功地应用在量子光学实验和量子密钥分配系统中,未来在量子信息技术等研究领域具有更广泛的应用.本文从超导TES单光子探测器的工作原理、制备流程、测试系统、主要性能指标以及研究现状和进展等方面对该探测器技术进行简要综述.