一种面向空间非合作目标位姿测量应用的三维点云滤波算法

针对激光位姿敏感器获得的原始点云有噪声和直接参与解算消耗星上计算资源过大问题,给出一种适用于空间非合作目标位姿测量的点云滤波和特征提取算法。应用仿真的方法分别验证了算法滤除空间随机噪声和点云降采样的有效性,验证了特征点对目标位姿变化和高斯测量噪声的鲁棒性。在非合作目标绕飞、抵近、捕获全物理试验平台上,以扫描激光位姿敏感器获得的原始点云数据为输入,验证了算法在实际空间目标位姿测量中的性能。试验结果表明,该算法实现了原始点云93.1%的降采样,节省了92.9%的位姿解算时间,可有效提升星上数据处理的效率和姿态解算的实时性。     

非临界压缩光场探测的实验方案研究

压缩态光场作为一种重要的量子光源,在量子计算、量子通信、精密测量等领域有广泛的应用前景.在非临界压缩光场产生的理论预测中,阈值以上泵浦的简并光学参量振荡器(DOPO)产生横向空间分布为一阶厄米高斯模式的非临界压缩光场,具有对泵浦光功率波动鲁棒性的量子特性,因此在实验中具有重要的应用价值.然而该非临界压缩光场的横向幅角随机旋转,导致无法利用本底探针光对其压缩特性进行稳定的平衡零拍实验探测.本文提出利用DOPO同时产生的与压缩光场空间正交的明亮光场作为本底探针光的实验探测方案.理论分析表明,该方案虽然引入了真空噪声,但可以很好地抵消压缩光场空间模式随机旋转引入的探测输出动态波动,得到3 d B的稳定探测结果,且对本底探针光的相位波动具有鲁棒性.因此该探测方案对于非临界压缩光场的实验研究具有重要的实用价值.     

光学简并三波混频中的量子非破坏测量

运用半经典量子理论方法建立了光学简并三波混频在两输入场均不为零的情况下的理论模型 ,讨论了在两输入场均不为零时系统的动力学行为以及相应的量子非破坏测量 (QND)特性。研究结果表明 ,该系统的最佳量子非破坏测量工作点与以往的情况不同 ,不是出现在非线性共振点处而是在双稳转变点     

基于条纹反射的非球面镜三维面形测量

提出一种利用条纹反射原理测量非球面镜的新方法.测量过程中,利用液晶屏显示正弦条纹,由摄像机记录由待测镜面反射产生的条纹图.并将显示屏和摄像机分别沿待测镜面轴向移动.摄像机在每个移动位置上,记录下显示屏移动前后产生的两幅条纹图.通过相移方法,得到条纹图的相位信息后,对摄像机上每个象素点,能在待测镜面卜找到一个对应待测点,并在获得该待测点的梯度信息的同时,获得该点位置坐标信息.最后通过积分,恢复待测镜面的三维高度信息.该方法不需辅助反射镜与干涉仪,能更加方便灵活地测量非球面镜.并且该方法有较好的抗噪性能,在噪声较大的情况下,仍能对非球面镜进行测量.模拟及初步实验均验证了该方法的可行性.     

光学简并三波混频中的最子非破坏测量

运用半经典量子理论方法建立了光学简并三波混频在两输入场均不为零的情况下的理论模型,讨论了在两输入场均不为零时系统的动力学行为以及相应的量子非测量（QND）特性。研究结果表明,该系统的最佳量子非破坏测量工作点与以往的情况不同,不是出现在非线性共振点处而是在双稳转变点。     

非探针近场光学显微镜的成像实现

介绍一种非探针近场光学显微镜，并对它的图像实现过程及处理方法进行了讨论。该装置以阿达玛变换成像理论为基础，用纳米多孔编码板代替光纤探针获得了较高的光学信噪比。成像研究表明，该装置可对近场衰逝波分量进行有效探测并能实现超衍射极限成像，为近场光学探测研究提供了一种新的思路。     

自适应非凸稀疏正则化下自适应光学系统加性噪声的去除

自适应光学系统可以实时测量并校正波前信息,但是系统中大量的噪声严重影响了系统的探测精度.自适应光学系统中一般为加性噪声,本文提出一种全新的变分处理模型去除加性噪声,该模型采用自适应非凸正则项.非凸正则项在保持图像细节上较凸正则项具有更好的效果,能更好地保持点源目标的完整性.另外,根据不同区域的噪声水平自适应地构建正则化参数,使不同区域的像素点受到不同程度的噪声抑制,可以更好地保持目标的边缘细节.在算法实现上,为了解决非凸正则项收敛性较差的缺陷,采用分裂Bregman算法及增广拉格朗日对偶算法进行计算.实验及数值仿真结果都表明,该方法能够较好地去除系统中的加性噪声,且光斑信号保存得较为完整,处理后的质心探测精度及信噪比较高.     

基于哈特曼波前传感器的非制冷红外成像光学读出系统

提出了一种新的基于哈特曼波前传感器(SHWS)的光学读出系统.该系统利用SHWS探测焦平面阵列(FPA)单元在受热前后反射波前斜率的变化量重构被探测物体的红外辐射图像.在理论上详细讨论其成像性能后,实验获得了单元尺寸为60 μm×60 μm,阵列大小为34 pixel×38 pixel的高温物体红外图像,其噪声等效温度差(NETD)约为3.8 K.优化系统参数设计,可以提高哈特曼波前传感器对到达角的测量精度进而获得更小的噪声等效温度差.     

四波混频光相位运算器原理及其噪声性能研究

推导了抽运消耗情形下简并和非简并四波混频(FWM)闲频光幅度和相位的统一解析表达式.采用极限方法,计算证明了非相敏放大模式下闲频光相位与输入光初始相位之间的关系,揭示了FWM相位加减混合运算器的工作原理.以四相相移键控信号为例,对基于非简并FWM的相位运算器进行了设计,重点分析了三种基本加减混合运算的噪声转移性能及其对光纤长度、输入光波长和功率的依赖特性.计算表明:该运算器的噪声指数约为1.1 dB;当输入光信号的信噪比大于24 dB时无纠错编码的符号错误率可低于10~(-3).     

非共线和频过程中的表面散射杂散光分析

以三次谐波自相关测量原理为出发点,研究了其和频过程中BBO晶体的表面散射杂散光。详细推导了由晶体表面散射引入的杂散光的具体表达式,定量分析了其对和频过程中输出信号的对比度的影响。分析表明,杂散光强度与晶体表面粗糙度有一定的关系。晶体表面粗糙度为激光波长的1%时,引入的杂散光噪声约为10-8。表面越光滑,引入的噪声越小。     

Measurement of intensity difference squeezing via non-degenerate four-wave mixing process in an atomic vapor

We report the measurement of the intensity difference squeezing via the non-degenerate four-wave mixing process in a rubidium atomic vapor medium. Two pairs of balanced detection systems are employed to measure the probe and the conjugate beams, respectively. It is convenient to get the quantum shot noise limit, the squeezed and the amplified noise power spectra. We also investigate the influence of the input extra quadrature amplitude noise of the probe beam. The influence of the extra noise can be minimized and the squeezing can be optimized under the proper parameter condition. We measure the -3.7-dB intensity difference squeezing when the probe beam has a 3-dB extra quadrature amplitude noise. This result is slightly smaller than -4.1 dB when the ideal coherent light （no extra noise） for the probe beam is used.     

Noise sensing via stochastic quantum Zeno

The dynamics of any quantum system is unavoidably influenced by the external environment. Thus, the observation of a quantum system (probe) can allow the measure of the environmental features. Here, to spectrally resolve a noise field coupled to the quantum probe, we employ dissipative manipulations of the probe, leading to so-called Stochastic Quantum Zeno (SQZ) phenomena. A quantum system coupled to a stochastic noise field and subject to a sequence of protective Zeno measurements slowly decays from its initial state with a survival probability that depends both on the measurement frequency and the noise. We present a robust sensing method to reconstruct the unknown noise power spectral density by evaluating the survival probability that we obtain when we additionally apply a set of coherent control pulses to the probe. The joint effect of coherent control, protective measurements and noise field on the decay provides us the desired information on the noise field.     

Telegraph noise in coupled quantum dot circuits induced by a quantum point contact

Charge detection utilizing a highly biased quantum point contact has become the most effective probe for studying few electron quantum dot circuits. Measurements on double and triple quantum dot circuits is performed to clarify a back action role of charge sensing on the confined electrons. The quantum point contact triggers inelastic transitions, which occur quite generally. Under specific device and measurement conditions these transitions manifest themselves as bounded regimes of telegraph noise within a stability diagram. A nonequilibrium transition from artificial atomic to molecular behavior is identified. Consequences for quantum information applications are discussed.     

Detection of 13.8 dB squeezed vacuum states by optimizing the interference efficiency and gain of balanced homodyne detection

Squeezed states belong to the most prominent non-classical resources. They have compelling applications in precise measurement, quantum computation, and detection. Here, we report on the direct measurement of 13.8 d B squeezed vacuum states by improving the interference efficiency and gain of balanced homodyne detection. By employing an auxiliary laser beam, the homodyne visibility is increased to 99.8%. The equivalent loss of the electronic noise is reduced to 0.05% by integrating a junction field-effect transistor(JFET) buffering input and another JFET bootstrap structure in the balanced homodyne detector.     

Correlation effects in light sources with high quantum efficiency

The noise properties of an LED with high quantum efficiency are investigated. Light with sub-Poissonian photon statistics is generated by driving the LED with a high impedance, well regulated current source. It is shown that it is necessary to distinguish between the measured total quantum efficiency and the optical quantum efficiency. In addition, the correlation between the fluctuations in the driving current and the fluctuations in the photocurrent is demonstrated, allowing a suppression of the shot noise after the measurement. The properties of this alternative noise reduction technique are discussed.     

Absolute detector calibration using twin beams

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.     

Optimum quantum state of light for gravitational-wave interferometry

The laser interferometric gravitational-wave detectors are sensitive to the quantum state of light employed in the dark port of interferometric system. In this paper a general quantum state for the dark input port is assumed. The quantum state of light is expanded versus the Fock states. The quantum noise of interferometric system is computed as a function of the quantum state of light. The variational method and the genetic algorithm are employed to determine the coefficients of the dark input port and the laser input power for the minimization of the quantum noise. Calculation shows that the optimum quantum state for the dark input port is very close to the vacuum squeezed state. For this optimum quantum state the quantum noise and optimum laser power reduces one order of magnitude relative to the conventional interferometer.     

Quantum state discrimination and enhancement by noise

Discrimination between two quantum states is addressed as a quantum detection process where a measurement with two outcomes is performed and a conclusive binary decision results about the state. The performance is assessed by the overall probability of decision error. Based on the theory of quantum detection, the optimal measurement and its performance are exhibited in general conditions. An application is realized on the qubit, for which generic models of quantum noise can be investigated for their impact on state discrimination from a noisy qubit. The quantum noise acts through random application of Pauli operators on the qubit prior to its measurement. For discrimination from a noisy qubit, various situations are exhibited where reinforcement of the action of the quantum noise can be associated with enhanced performance. Such implications of the quantum noise are analyzed and interpreted in relation to stochastic resonance and enhancement by noise in information processing.     

Switching noise as a probe of statistics in the fractional quantum Hall effect

We propose an experiment to probe the unconventional quantum statistics of quasiparticles in fractional quantum Hall states by measurement of current noise. The geometry we consider is that of a Hall bar where two quantum point contacts introduce two interfering amplitudes for backscattering. Thermal fluctuations of the number of quasiparticles enclosed between the two point contacts introduce current noise, which reflects the statistics of the quasiparticles. We analyze Abelian nu=1/q states and the non-Abelian nu=5/2 state.     

Approaching Quantum-Limited Amplification with Large Gain Catalyzed by Optical Parametric Amplifier Medium

Amplifier is at the heart of experiments carrying out the precise measurement of a weak signal. An idea quantum amplifier should have a large gain and minimum added noise simultaneously. Here, we consider the quantum measurement properties of the cavity with the OPA medium in the op-amp mode to amplify an input signal. We show that our nonlinear-cavity quantum amplifier has large gain in the single-value stable regime and achieves quantum limit unconditionally.