门控下InGaAs/InP单光子探测器用于符合测量的时域滤波特性研究

基于砷化镓/磷化铟雪崩光电二极管(InGaAs/InP APD)的半导体单光子探测器因工作在通信波段,且具有体积小、成本低、操作方便等优势,在实用化量子通信技术中发挥了重要作用.为尽可能避免暗计数和后脉冲对单光子探测的影响,InGaAs/InP单光子探测器广泛采用门控技术来快速触发和淬灭雪崩效应,有效门宽通常在纳秒量级.本文研究揭示了门控下单光子探测器可测量的最大符合时间宽度受限于门控脉冲的宽度,理论分析与实验结果良好拟合.该研究表明,门控下InGaAs/InP单光子探测器用于双光子符合测量具有显著的时域滤波特性,限制了其在基于双光子时间关联测量的量子信息技术中的应用.     

基于超导探测器的激光测距系统作用距离分析

提出了将超导纳米线单光子探测器(SSPD)应用于空间碎片激光测距的构想,并通过理论分析和等效外场实验进行了可行性论证。根据SSPD在门控时间内允许多次测量的特性,建立了信噪比随回波光子数的变化模型,并考察了激光器发射重复频率、天光背景噪声强度、探测器暗计数率等参数对信噪比的影响,结合回波光子数方程和噪声强度,以云南天文台激光测距系统为例,推算出该系统具备探测830 km处米级大小空间碎片的能力。结合光纤耦合条件,设计了以太阳能板为目标的外场实验,通过改变光学系统透过率,获得了信噪比随回波光子数变化的实验曲线,验证了利用信噪比变化推测系统作用距离方法的有效性,理论和等效实验结果均表明超导纳米线探测器有望实现空间碎片激光测距。     

超导纳米线多光子响应特性研究

研究了超导单光子探测器器件超导纳米线的多光子响应特性.在温度3.5 K实验测量了纳米线器件直流特性和比子响应概率对多光子脉冲信号的响应特性.实验表明,器件超导转变电流随光辐照强度的增加而减小;在多光子脉冲信号下,器件响应的光子数随偏置电流减小而增加.同时基于量子光学和器件Hotspot理论半定量分析了该多光子响应的机制.     

近红外单光子探测器

该单光子探测器在实验中使用半导体制冷器制冷，雪崩二极管工作于盖革模式下，使用交流耦合方式提供门脉冲信号，通过延迟补偿和采样门控消除尖脉冲干扰，采用反馈门控减小后脉冲影响，优化电路参数减小暗计数.经实验测试与分析，温度在-62.5℃，门脉冲宽度为50ns，采样门控为10ns的条件下，最佳工作点的暗计数率小于4×10^-6ns^-1，量子效率约18%，噪声等效功率为2.4×10^-19W/Hz^1/2.     

超导动态电感单光子探测器的噪声处理

噪声是影响弱信号检测器件性能指标的主要因素之一,而最优滤波算法是白噪声背景中自适应提取弱有用信号的一种常见处理方法.本文针对极低温环境下微波动态电感探测器(microwave kinetic inductance detector, MKID)光子弱信号响应的噪声特性,在改进噪声模型的基础上利用最优滤波算法改进了探测信号的噪声处理.结果表明,经过改进噪声模型的算法处理, MKID的能量分辨(单光子探测器的主要性能指标之一)得到了15%左右的提升,实现了0.26 e V的红外单光子能量分辨.     

单光子激光测距的漂移误差理论模型及补偿方法

单光子激光测距系统采用高灵敏度的单光子探测器作为接收器件,更易实现高密度、高覆盖率的目标采样,是未来激光测距系统的发展方向.漂移误差作为限制单光子激光测距精度提高的瓶颈问题,其主要由平均回波信号光子数的变化引起.以激光雷达方程、单光子探测器的概率与统计理论为基础,建立了漂移误差的理论模型,给出了漂移误差与平均信号光子数、均方根脉宽等系统参数之间的理论关系式.同时,结合单光子探测概率模型给出了一种漂移误差的修正方法,并搭建实验系统对漂移误差模型和修正方法进行了验证.在回波信号均方根脉宽为3.2 ns、平均回波信号光子数为0.03到4.3个情况下,未经修正的漂移误差最大达到46 cm,经修正后的均方根误差为1.16 cm,平均绝对误差为0.99 cm,达到1 cm量级,漂移误差对测距精度的影响基本可以忽略.该方法可以解决漂移误差制约单光子激光测距精度提高的瓶颈问题.     

基于单光子探测的高精度长距离光纤双向时间比对

在长距离光纤时间传递链路中,为了避免使用中继放大导致双向传输时延不对称以及引入附加的噪声,提出一种基于单光子探测的长距离光纤时间传递方案。将经过主端（从端） 1 pulse/s时间信号控制的激光脉冲序列作为发送信号,利用从端（主端）具有极高探测灵敏度的单光子探测器接收到达信号,并基于双向时分复用同纤同波时间比对方案得到双向光纤链路传输时延变化,进而根据时间相关单光子计数和高斯拟合的数据处理方式得到两端之间钟差的时间稳定度。为了实现单光子探测器在门控模式下对长距离光纤实验系统的长期测试,设计并实现了外部触发门控工作方式下动态调整的触发控制系统。通过利用光纤链路传输时延变化量,实现对门控触发信号的控制。350 km单模光纤和对应长度的色散补偿光纤（链路总损耗约为100 dB）的时间传递系统实验结果表明,时间传递稳定度优于1.5 ps@1 s和0.4 ps@8192 s。所提方法为长距离高精度光纤时间传递提供了一种有效的解决方案。     

纠缠光子法绝对定标光电探测器量子效率的研究

为了应对国际上“坎德拉”新定义的动向,开展了利用纠缠光子法测量光电探测器量子效率的研究,并建立了测量装置。装置采用351.1 nm连续激光抽运BBO晶体产生纠缠光子场,然后通过双通道门控计数器组成的符合测量系统在702.2 nm和788.7 nm两个波长点对光电倍增管的量子效率进行了测量。同时对单光子脉冲信号获取、噪声抑制及提取、符合时间特性、偶然符合、暗背景计数和器件透过率等影响测量结果的关键因素进行了实验分析并给出了修正分量,最终在两个波长点量子效率测量不确定度小于0.7%。     

实验条件不完美对薛定谔猫态制备的影响

薛定谔猫态是一类重要的非经典光场,实验上可以通过真空压缩态减光子的方案获得.本文从理论上研究了实验条件对制备薛定谔猫态的影响,主要考虑了包括压缩态的压缩度和纯度、单光子探测器的效率及噪声以及零拍探测器的效率等诸多因素的影响.理想情况下通过减光子方案制备得到的薛定谔猫态为奇光子数态,其相空间原点的Wigner函数为负值是其非经典特性的重要判据,而保真度可以度量制备态与理想猫态之间的相似程度.在压缩态为非纯态以及单光子探测器为商用低效率阈值探测器的情况下,计算了制备猫态的保真度、Wigner函数及其相空间原点处W（0）的表达式,分析了实验条件对薛定谔猫态制备的影响,为制备高质量的薛定谔猫态提供了理论指导.     

空间X射线通信链路建模与功率分析

从空间X射线通信传输理论出发,首先对X射线通信的功率传输过程进行研究,以加性高斯白噪声信道模型与自由空间损耗为基础,分析了深空X射线通信的信道特征及功率传输过程、推导了功率传输方程,建立了通信链路模型;其次,分析了深空X射线通信系统的误差来源,建立了基于单光子探测器的噪声模型,并给出了主要噪声来源的数学表达式,从而确定了通信核心参数通信距离、通信速率、误码率与信号功率之间的关系;最后,对不同阳极高压与不同调制方式下探测器端信号光子数进行实验监测,对功率传输方程及误差模型进行验证.实验结果表明,所给出的功率传输方程与误差模型可以对空间X射线通信过程进行较好地解释.根据此模型,计算了在满足一定的误码率和传输距离要求时对X射线源出射功率的要求,为空间X射线通信研究建立了理论基础,为核心元器件的研究指明了下一步的方向,同时有望对空间X射线通信的工程化提供一定的参考.     

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.     

Photon echo peak shift experiments in the UV: p-terphenyl in different solvents

In this article we present a new photon echo set-up operating in the UV range and our first results of photon echo peak shift (PEPS) experiments of a small non-polar dye molecule, p-terphenyl (pTP), in three different solvents: ethanol, methanol and 2-propanol. The experiments show the feasibility of UV transient grating and photon echo measurements and highlight the sensitivity of this technique for the study of non-polar solvation dynamics. The transient grating experiments indicate a relaxation of the ground state hole of about 6 ps. The photon echo experiments show that while electronic dephasing occurs on timescales shorter than 100 fs, solvation dynamics timescales are in the picosecond regime, in agreement with the literature.     

Avalanche mechanism analysis of 4H-SiC n-i-p and p-i-n avalanche photodiodes working in Geiger mode

Understanding detailed avalanche mechanisms is critical for design optimization of avalanche photodiodes(APDs). In this work, avalanche characteristics and single photon counting performance of 4 H-Si C n-i-p and p-i-n APDs are compared. By studying the evolution of breakdown voltage as a function of incident light wavelength, it is confirmed that at the deep ultraviolet(UV) wavelength region the avalanche events in 4 H-Si C n-i-p APDs are mainly induced by hole-initiated ionization,while electron-initiated ionization is the main cause of avalanche breakdown in 4 H-Si C p-i-n APDs. Meanwhile, at the same dark count rate, the single photon counting efficiency of n-i-p APDs is considerably higher than that of p-i-n APDs. The higher performance of n-i-p APDs can be explained by the larger impact ionization coefficient of holes in 4 H-Si C. In addition, this is the first time, to the best of our knowledge, to report single photon detection performance of vertical 4 H-Si C n-i-p-n APDs.     

Linear optical implementation of optimal unambiguous discrimination among quantum states

In this paper, we present a linear optical scheme for optimal unambiguous discrimination among nonorthogonal quantum states in terms of the multiple-rail and polarization representation of a single photon. In our scheme, discriminated quantum states are expressed by using the spatial degree of freedom of a single photon while the polarization degree of freedom of the single photon is used to act as an auxiliary qubit. The optical components used in our scheme are only passive linear optical elements such as polarizing beam splitters, wave plates, polarizers, single photon detectors, and single photon source.     

用于红外单光子探测的雪崩光电二极管传输线抑制电路模型的理论分析

结合利用雪崩光电二极管(APD)进行红外单光子探测电路模型的工作原理和特点以及传输线瞬态电脉冲产生的过程,提出了将传输线瞬态过程脉冲发生电路模型用于APD雪崩抑制的一种新方法,该方法可以实现利用APD门模工作方式进行红外单光子探测的过程.主要从理论上计算了红外单光子信号入射APD时,传输线脉冲发生电路模型中负载电阻输出电脉冲的特点,讨论了传输线终端不同边界条件对输出电脉冲的影响,通过理论计算确定了这种利用APD进行红外单光子探测新模型的电路结构与参数,证明了该电路模型用于红外单光子探测APD门模工作方式的 关键词： 红外单光子探测技术 雪崩光电二极管(APD) 抑制电路 传输线瞬态过程     

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。     

Plasmonics properties of nano-torus: An FEM method

Nano-torus particles are promising in nano-photonics applications. In this paper, we investigate the plasmonics resonant spectrum of torus and the corresponding horizontal and vertical dimers with the finite element method (FEM) based on strict electromagnetic theory. Compared with sphere, single torus and horizontal dimer under perpendicular polarization are characterized with narrower line width and wider tunability throughout visible and infrared frequencies. These properties make single torus and horizontal dimer suitable for high sensitivity sensing. Furthermore, Purcell factor and local field enhancement of horizontal dimer which are important to high efficient single photon devices are one order of magnitude higher than those of single torus respectively. However, vertical dimer under perpendicular polarization has no above advanced characteristics.     

两个独立全光纤多通道光子纠缠源的Hong-Ou-Mandel干涉

独立光子源的干涉是实现复杂量子体系应用(比如多光子纠缠态产生和量子隐形传态等)的核心技术.利用100 GHz密集波分复用技术,实现了1.55μm全光纤多通道独立纠缠光子源的Hong-Ou-Mandel干涉,在不去除暗符合(随机符合计数)的情况下,可见度为53.2%±8.4%,去除暗符合可见度可达到82.9%±5.3%.给出了关于色散位移光纤中基于自发四波混频过程产生的单光子光谱纯度严格的理论描述,模拟了抽运脉冲宽度和滤波器带宽对单光子光谱纯度的影响,并给出了理论上的最佳条件(最佳的抽运脉冲宽度为8 ps,高斯滤波器带宽为40 GHz及以下).在测量Hong-Ou-Mandel干涉之前,先测量了液氮冷却状态下的色散位移光纤关联光子源的符合和随机符合比率,在抽运功率为23μW的情况下,最大比率可以达到131.Hong-Ou-Mandel干涉在高精度光学测量、测量装置无关的量子密钥分配等应用中扮演着极为重要的角色.     

Gravitational field from photons

The gravitational field created by a single photon is determined by taking into account the relativistic mass of the photon as source of gravitational interaction. In addition, the total force (due to the above field) over an accelerated particle is calculated in the light of the general theory of relativity. Some aspects related to the photon as an ultrarelativistic particle are discussed.     

The electron’s self photon

Equations of motion (EOM’s) are presented for the electron and photon. The electron EOM is the same as Dirac’s equation with mass interpreted to be totally electromagnetic in nature. The photon EOM is considered here to be the EOM for the electron’s self photon. The electron EOM and photon EOM together are presented as a single theory of the electron which is distinct from QED, in which separate matter and light theories are used for the electron and photon respectively.A temporarily bound state is found for the point proton-electron-self-photon three-body combination which possibly represents a neutronic state. In support of this surmise the theory is used to calculate the neutronic state-proton mass difference, the lifetime of the neutronic state against electron emission, and the neutronic state’s magnetic moment. This interpretation of the neutronic state suggests that the self photon and the neutrino share the same EOM and are possibly the same particle.