单光子探测器量子效率的自绝对标定

单光子探测器日益广泛地应用于科学研究的各个领域，精确地标定其量子效率成为应用的先决条件。我们首次实现了单光子探测器量子效率自绝对标定的原理性实验，即只利用待测探测器本身就可以对其量子效率进行绝对标定，而不需要第二个探测器或任何参考标准。该方法基于自发参量下转换产生的纠缠光子对的时间关联性，在信号光子和闲散光子之间引入延时，由单光子计数率和符合计数率测得探测器的量子效率。     

单光子探测器量子效率绝对自身标定方案

参考已有的方案,提出了一种更简单的方案来实现单光子探测器量子效率的绝对自身标定。我们利用同轴线缆和数据采集卡代替已有方案中的符合测量电路和计数器,通过精确设定同轴线缆的长度,利用电脉冲在同轴线缆的短路终端反射回波的特性,对一个测量周期中单个脉冲和连续两个脉冲进行区分,用数据采集卡记录区分结果,分别得到探测器探测到两个孪生光子的计数和仅探测到其中任意一个光子的计数,从而算出单光子探测器的量子效率。此方案不需要其他任何的参考标准或者另一个探测器.     

基于相关光子的单光子探测器量子效率测量系统

为准确测量近红外波段单光子探测器量子效率,搭建了基于自发参量下转换效应的测量系统.系统利用中心波长为518nm的脉冲激光泵浦周期极化磷酸氧钛钾晶体,通过自发参量下转换过程产生相关光子对,分别测量了Si和InGaAs雪崩光电二极管单光子探测器在778nm和1 550nm波长点的量子效率,并对测量不确定度进行了分析.实验表明,该装置可以测量近红外单光子探测器量子效率参量,测量不确定度均优于1%.     

相关光子定标的符合测量精度分析

采用355nm连续激光泵浦BBO晶体产生参量下转换效应,搭建了相关光子辐射定标实验装置,使用时间数字转换和时间幅度转换两种符合测量方法进行比对测量,定标了不同光子速率下雪崩光电二极管在737nm波段的探测效率,分析了在高光子计数率下死时间和后脉冲等因素对符合测量选取符合门宽和意外符合的影响,比较了不同光子计数速率的测量结果并分析符合测量的修正因素,修正后两种测量结果的相对偏差优于0.25%.采用时间间隔技术测量了不同光子计数率的后脉冲概率,为提高单光子探测器的计数精度和相关光子定标的精度提供依据.     

安徽量子通信技术有限公司

<正>量子密钥分发实验系统(BB84)利用量子态的不确定原理、量子态不可克隆原理、量子不可分原理等,将信息编码在单光子的量子态上,可完成量子密钥分发,结合一次一密的加密方式,可实现理论上的无条件安全保密通信。搭建量子密钥分发实验光路学习量子密钥分发BB84协议掌握量子信息编码方法实现量子保密通信全过程开发量子保密通信新的应用小型纠缠源实验系统性能指标波长:810nm。单路计数率:100kps符合计数率:6kps纠缠品质:92%泵浦光功率:0~100mw符合计数器门宽:3ns~10ns应用高亮纠缠光子源高亮单光子源量子成像极化关联曲线实验四种Bell态的制备Bell不等式测量单、双光子干涉实验     

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%。     

基于探测器模型的MPPC标定方法

探测器的光子数分辨能力是精确描述多光子态的突破口,近年来受到广泛的关注。光子数可分辨探测器有望被进一步应用于量子光学基础研究、量子成像、量子计算、量子通讯以及远距离激光测距等领域。基于空间复用原理的多像素光子计数器具有常温下稳定高效的光子数可分辨探测能力,加上尺寸和成本上的优势使得它成为光子数可分辨探测应用的首选。针对多像素光子计数器,我们通过建模给出了能描述探测器量子特性的标准矫正方法,系统地考虑了探测器量子效率、噪声、各像素点感光面的光子入射效率对量子特性的影响,给出了不同光子数态的正定算子估值测量和魏格纳函数。     

基于相关光子多模式相关性的InSb模拟探测器定标方法

利用基于参量下转换产生的相关光子可以实现“无溯源”的绝对定标. 将该方法推广应用于模拟探测器定标的过程中, 获取两路模拟光电流信号的有效相关信息是主要难点. 在相关光子的多模式相关性理论模型的基础上, 提出了一种新的光电流处理方案. 通过将某一时刻采集到的光电流所包含的电荷量转换为等效光子计数, 采用双光路平衡探测和双通道数据波动校正的技术思路, 开展了红外模拟探测器量子效率定标验证实验研究. 利用532 nm单波长激光器为抽运源、PPLN晶体为非线性晶体, 在25 ℃工作温度下获取了631和3390 nm的相关光子对, 定标了InSb红外模拟探测器在3390 nm处的绝对功率响应度. 结果表明, 对InSb模拟探测器的合成不确定度为7.785%. 根据量子效率与绝对功率响应度之间的函数关系, 定标结果与国内计量单位的校准结果的相对偏差为3.6%. 利用多模式相关性在模拟信号下实现红外模拟探测器的绝对功率响应度定标在国际上暂无此方面的报道, 该方法验证了应用多模式相关性理论开展模拟探测器定标方法的可行性, 对于探索基于相关光子的定标技术和拓宽辐射定标应用领域具有重要意义.     

泵浦光的入射角对参量下转换的影响

利用参量下转换制备相关光子实现对各类探测器的量子效率的定标,是近年来兴起的新型定标技术。由于参量下转换的光子转换效率低,探测器输出信号信噪比小。采用短波激光器泵浦PPLN周期极化性晶体,可获得较大功率的参量光。分析了泵浦光在PPLN晶体端面的入射角对参量光的转换效率、空间分布、参量带宽及晶体周期的影响,并进行了数值模拟。分析发现当泵浦光正入射晶体端面时,参量光功率转换大,带宽小,发散角大;随着泵浦光入射角度逐渐增大,参量下转换的转换效率降低,相关光子的带宽变小,发散角变小且参量光的中心波长的空间位置会发生相对偏移。该研究结果可为相关光子探测、模拟探测器量子效率的高精度定标提供理论依据。     

基于连续和脉冲激光泵浦的相关光子实验比对

为在相关光子定标技术工程化过程中选择合适的泵浦机制及相位匹配模式,开展了基于连续和脉冲激光的相关光子比对实验.采用355nm连续激光泵浦偏硼酸钡晶体产生相关光子对,对晶体吸收、透射损耗以及光学元件透过率进行测量和修正,同时使用基于时间幅度转换的符合测量方法,得到单光子探测器量子效率为59.15%.利用518nm脉冲激光泵浦周期极化磷酸钛氧钾晶体,采用准相位匹配技术获取相同波段的相关光子,基于时间幅度转换的符合测量方法得到单光子探测器量子效率为59%.比对实验结果,两套定标装置方法的测量结果之差在0.25%以内,主要误差来源于单光子探测器的响应非线性、光路透过率修正误差和单光子探测量子效率面非均匀性.实验结果验证了相关光子定标技术可随时随地复现的优点,以及相关光子定标结果不受泵浦机制差异和实验装置差异的影响,可为相关光子技术工程化中的激光器工作模式和相位匹配方式的选择提供参考依据.     

超短光脉冲波形对门模单光子探测的影响

采用两种不同的皮秒光脉冲波形进行了门模单光子探测实验.测量了单光子探测效率随探测器和超短脉冲光源之间的同步延迟细微调节时的变化曲线.结果表明：光脉冲波形直接影响光子到达时间与门脉冲时间窗口之间的精确同步和探测效率,使用其中一种脉宽较短的皮秒光脉冲时探测效率比使用另一种脉冲提高了约9%.     

一种新的预报单光子源诱骗态量子密钥分发方案

提出一种新的预报单光子源诱骗态量子密钥分发方案.在发端采用参量下变换产生纠缠光子对,其中之一用来进行预报探测,根据探测结果将另一路光脉冲分成两个集合,其中预报探测有响应的脉冲集合用作信号态,无响应的脉冲集合作为诱骗态.由于探测效率的问题,这两个集合都是有光子的,通过这两个集合的通过率和错误率估计出单光子的通过率和错误率.此方法不需要改变光强,简单可行.仿真结果表明：该方法可以达到完美单光子源的安全通信距离;与预报单光子源的量子密钥分发相比,密钥产生率有了很大的提高;和三强度预报单光子源诱骗态量子密钥分发的 关键词： 量子保密通信 量子密钥分发 诱骗态 预报单光子源     

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.     

Carrier transport and its effect on the turn-on delay time in strained GalnAsP/InP multiple quantum well lasers

The effects of carrier transport on turn-on delay time in multiple quantum well lasers were investigated both theoretically and experimentally. By using rate equation analysis with two components of the carrier density inside and outside of the quantum wells, we found that carrier transport caused two important effects: one is the stationary effect of a significant reduction in carrier density in quantum wells; the other is an increase in differential carrier lifetime.As an experimental investigation, compressively strained 1.3 m GalnAsP/InP multiple quantum well (MQW) lasers were fabricated and their turn-on delay times were measured and investigated. The short-cavity buried-heterostructure lasers showed low-threshold current (2 to 3 mA) and small turn-on delay time (<200 ps) at biasless 30 mA pulse current. Although these performances are suitable for high-speed digital transmission, it was found that the carrier lifetimes derived from the turn-on delay measurement were larger for strained quantum well lasers than for conventional quantum well lasers and double heterostructure lasers. These phenomena are explained using the carrier transport model and are discussed. The solutions for further reduction in carrier lifetime and turn-on delay are discussed.     

Causality, relativity and quantum correlation experiments with moving reference frames

Entanglement, one of the most important features of quantum mechanics, is at the core of the famous Einstein-Bohr philosophical debate [1] and is the principal resource for quantum information processing [2]. We report on new experimental investigations of the properties of entangled photon pairs with emphasis on the tension between quantum mechanics and relativity [3,4]. Entangled photons are sent via an optical fiber network to two villages near Geneva, separated by more than 10 km where they are analyzed by interferometers [5]. The photon pair source is set as precisely as possible in the center so that the two photons arrive at the detectors within a time interval of less than 5 ps (corresponding to a path length difference of less than 1 mm). This sets a lower bound on the ‘speed of quantum information’ to 10⁷ times the speed of light. Next, one detector is set in motion [6] so that both detectors, each in its own inertial reference frame, are first to do the measurement! The data always reproduces the quantum correlations.     

Two‐color operation of a free‐electron laser with a tilted beam

With the successful operation of free‐electron lasers (FELs) as user facilities there has been a growing demand for experiments with two photon pulses with variable photon energy and time separation. A configuration of an undulator with variable‐gap control and a delaying chicane in the middle of the beamline is proposed. An injected electron beam with a transverse tilt will only yield FEL radiation for the parts which are close to the undulator axis. This allows, after re‐aligning and delaying the electron beam, a different part of the bunch to be used to produce a second FEL pulse. This method offers independent control in photon energy and delay. For the parameters of the soft X‐ray beamline Athos at the SwissFEL facility the photon energy tuning range is a factor of five with an adjustable delay between the two pulses from ?50 to 950 fs.     

Impact of picosecond laser pulse waveform on detection efficiency of gated-mode avalanche photodiodes for quantum key distribution

Detection efficiency is one of the key parameters that affect the performance of gated-mode avalanche photodiodes in quantum key distribution. In this paper, the impact of the waveform of faint picosecond laser pulses on detection efficiency is investigated both experimentally and analytically. Two kinds of laser pulses are attenuated to the single photon level to measure and plot single photon detection efficiency versus synchronous delay between the detector and the laser source. The results show that the narrower laser pulse with single peak can be detected with about 9% higher detection efficiency and lead to a lower QBER than the pulse with subpeak and a broadened pedestal.     

Heralded linear optical quantum Fredkin gate based on one auxiliary qubit and one single photon detector

Linear optical quantum Fredkin gate can be applied to quantum computing and quantum multi-user communication networks. In the existing linear optical scheme, two single photon detectors （SPDs） are used to herald the success of the quantum Fredkin gate while they have no photon count. But analysis results show that for non-perfect SPD, the lower the detector efficiency, the higher the heralded success rate by this scheme is. We propose an improved linear optical quantum Fredkin gate by designing a new heralding scheme with an auxiliary qubit and only one SPD, in which the higher the detection efficiency of the heralding detector, the higher the success rate of the gate is. The new heralding scheme can also work efficiently under a non-ideal single photon source. Based on this quantum Fredkin gate, large-scale quantum switching networks can be built. As an example, a quantum Bene~ network is shown in which only one SPD is used.     

New high-efficiency source of photon pairs for engineering quantum entanglement.

We constructed an efficient source of photon pairs using a waveguide-type nonlinear device and performed a two-photon interference experiment with an unbalanced Michelson interferometer. As the interferometer has two arms of different lengths, photons from the short arm arrive at the detector earlier than those from the long arm. We find that the arrival time difference (Delta L/c) and the time window of the coincidence counter (Delta T) are important parameters which determine the boundary between the classical and quantum regimes. Fringes of high visibility ( 80% +/- 10%) were observed when Delta T < Delta L/c. This result is explained only by quantum theory and is clear evidence for quantum entanglement of the interferometer's optical paths.