大气闪烁对纠缠相干态量子干涉雷达影响机理

介绍了量子干涉雷达物理模型及其探测原理,并采用耗散-涨落通道处理量子光场在湍流大气中的传输,从经典湍流统计理论推导得到大气透射率的概率密度分布函数P(T),以此为基础系统分析了大气闪烁效应对纠缠相干态量子干涉雷达的影响机理,深入讨论了平均大气透射率、闪烁指数等大气参数对系统目标探测性能的影响.研究发现:低损耗情况下系统灵敏度及分辨率性能随闪烁指数的增加而降低;高损耗情况下大气闪烁则能显著提高系统灵敏度和分辨率性能,且界定高低损耗的透射率临界点随脉冲光子数增加而增加,故大气闪烁能够在一定程度上克服大气损耗造成的不良影响.     

损耗与噪声对分束器的量子非破坏性测量的影响

采用量子理论详细地分析有损耗的分束器作为量子非破坏性测量系统时的量子态制备能力和量子光学分流能力与透射损耗和反射损耗的关系.给出当输入探测光的量子起伏为某一确定值时,要实现量子非破坏性测量分束器损耗的上限值.还讨论输人信号光不是相干态而是含有热噪声的相干信号场时,信号光的量子起伏对量子非破坏性测量的影响. 关键词：     

基于量子照明的导航测距方案

针对以往脉冲纠缠测距方案对光子损耗十分敏感的特点及量子干涉法测距中利用光路延迟测距时难以实现远距离传输的问题,利用量子压缩效应来提升时延估计精度,同时还提出一种基于量子照明原理的非经典纠缠导航测距方案,对目标存在的回波信号进行统计判断,从而确定距离参数。在相干探测的基础上,分别研究了相干态、热态和压缩态等3种高斯量子态的统计特性,并对量子照明测距方案中经典相干态与双模压缩真空态的信号检测性能进行了理论分析和数值模拟实验。结果表明,相较于传统测距方法,利用量子信号压缩和纠缠特性的方法能有效提高导航测距的距离分辨率,性能上优于经典方案,且在噪声光子数较多时具有更强的抗环境干扰能力。     

自然环境中多因子对自由空间量子通信性能的影响

根据大气中尺寸与光波长相近的各粒子的粒度谱分布函数,分析了大气湿度、粒子浓度、光信号波长和粒子直径等因子与量子弱相干光信号的衰减关系.讨论了多环境因子对大气能见度的影响,得到平流层量子通信中大气能见度和探测望远镜倾角对链路衰减的影响,量子信号传输误码率、保真度与大气能见度和传输距离的定量关系.仿真实验表明,随着大气湿度和粒子浓度的增加,量子信号传输的链路衰减逐渐增加,当光信号波长与粒子直径相近时,衰减最显著;在传输距离为15km,望远镜倾角为90°的前提下,当大气能见度分别为5km和15km时,链路衰减依次为18.9dB和14.2dB,信道误码率分别为0.010 5和0.009 9,信号保真度分别为0.22和0.71.     

直接探测激光测风雷达发射激光线宽对探测的影响

 论述了Rayleigh散射双边缘直接探测激光测风雷达发射激光线宽对探测灵敏度和误差的影响。使用Monte-Carlo方法模拟了大气后向散射回波半高宽(FWHM)和发射激光线宽的定量数值关系。把这个关系拟合为一个二次多项式,计算了由发射线宽引起的测量灵敏度和误差。对于探测波长是355 nm的情况,当发射线宽从单频增加到2 GHz时,后向散射回波线宽从3.853 GHz非线性地增加到5.371 GHz。发射激光线宽的加宽对探测影响很大,当发射线宽从单频增加到2 GHz时,测量灵敏度从0.003 1降低到0.001 9,测量误差从0.323 m/s增大到0.518 m/s,计算中假定探测信噪比和累计激光脉冲数都是1 000。     

基于外差干涉的微振动测量技术研究

针对外差干涉的微振动测量存在稳定性低、严重受环境噪声影响等缺点,提出了对光路的改进方案。根据差分原理将其改为双光路,消除环境噪声的干扰;通过偏振分光棱镜（PBS）将椭圆偏振光变为线偏光,提高干涉信号幅值;改进频移装置(AOM),抑制频率漂移;增加光阑,滤除杂散光,提高系统信噪比。通过探测5 kHz压电陶瓷振动信号,以及2.5 MHz高频激光超声信号进行实验验证,结果表明:信号稳定且无纹波,系统分辨率为2.3 nm,信噪比提高16.7倍。两路干涉信号幅值分别为552 mV和736 mV,较传统外差干涉信号幅值提高近10倍,有利于纳米量级微振动信号的检测。     

基于光纤马赫-曾德尔干涉仪的强度测量研究

根据光外差检测原理，分析得到干涉测量适用于信号光强小于参考光强的探测，直接测量适用于信号光强大于参考光强的探测的结论。利用自制的全光纤马赫-曾德尔干涉仪系统，对位移信号进行了测量。实验结果表明：当位移信号较小时，干涉测量的灵敏度分别为62．068μW／mm和9．90mV／mm，而非干涉测量的灵敏度分别为4．30μW／mm和0．35mV／mm；当位移信号较大时，干涉测量的灵敏度分别为2．643mV／mm和0．055mV／mm，非干涉测量的灵敏度分别为12．326mV／mm和4．194mV／mm，测量结果与分析得到的结论一致。对于光纤干涉仪强度调制检测的应用具有参考价值。     

高光谱分辨率激光雷达鉴频器的设计与分析

提出了利用Fabry-Perot干涉仪的反射场实现高光谱分辨率激光雷达精细探测大气光学参量的新方法和思路.设计了高光谱分辨率的分光系统,并分析了干涉仪反射场的光谱透过特征曲线.结合高光谱激光雷达探测信号特征,讨论分析了谱分离比和瑞利信号透过率随反射率和腔长的变化曲线,同时结合误差传递公式,建立了仿真分析模型,讨论了回波光束发散角和入射角变化对激光雷达探测结果的影响.结果表明,所提出的Fabry-Perot干涉仪反射场可以实现高光谱分辨率激光雷达探测系统的精细分光,同时探测结果误差随回波光束发散角变化不敏感,控制发散角在10 mrad以内,入射角在1.5 mrad以内时,可以实现气溶胶光学参数廓线的高精度探测.     

基于本征荧光的生物气溶胶测量激光雷达性能

为研究本征荧光对生物气溶胶粒子探测精度的影响,本文在阐述生物气溶胶荧光光谱信号探测原理的基础上,设计了一台紫外激光诱导荧光雷达.该雷达选用波长为266 nm的四倍频固体激光器作为激励光源,基于本征荧光波长、探测距离等主要参数,对生物气溶胶荧光光谱回波信号的信噪比及粒子浓度的最小分辨率进行数值仿真分析.仿真结果表明,在探测误差小于10%的情况下,距离为1.5 km时,系统对生物气溶胶荧光波长的有效探测范围为300—800 nm;而在距离为2.1 km时,荧光波长的有效探测范围为300—310 nm.此外,在探测距离定义为0.1 km,荧光波长为350和600 nm时,系统对物气溶胶粒子浓度的最小分辨率分别为2个颗粒/L和4个颗粒/L,最小分辨率的差值为2个颗粒/L.仿真结果有利于了解荧光波长变动时激光雷达系统的探测准确度,进而实现大气生物气溶胶更加有效的探测.     

全光纤M-Z干涉仪的高灵敏度与大动态范围多普勒激光雷达风场探测技术

多普勒测风激光雷达是大气风场探测的重要手段之一。通过检测风速导致的大气后向散射谱的多普勒频移从而实现风速的探测。由于受鉴频器本身特性的影响,高灵敏度与大动态范围的探测一直是大气风场探测的难点。提出采用双光纤Mach-Zehnder干涉仪(FMZI)作为多普勒激光雷达的鉴频器件,设计两路不同动态范围及风速探测灵敏度的FMZI鉴频器同时对大气回波信号进行鉴频。采用小光程差(13.7 cm)、大动态范围(±100 m·s-1)鉴频光路FMZI-2对风速区间进行定位,大光程差(74.8 cm)、高探测灵敏度(2.62%/(m·s-1))的鉴频光路FMZI-1进行风速精细探测,从而实现大动态范围高灵敏度的风场探测。利用标准大气模型对不同参数条件下的系统灵敏度、系统探测的信噪比及风速误差进行仿真分析。结果表明,该系统可以实现±100 m·s-1大动态范围内风速误差小于1 m·s-1的大气风场探测,为大动态范围高灵敏度测风激光雷达的发展进行了有益的探索。     

The parity operator in quantum optical metrology

Photon number states are assigned a parity of +1 if their photon number is even and a parity of ?1 if odd. The parity operator, which is minus one to the power of the photon number operator, is a Hermitian operator and thus a quantum mechanical observable although it has no classical analogue, the concept being meaningless in the context of classical light waves. In this paper we review work on the application of the parity operator to the problem of quantum metrology for the detection of small phase shifts with quantum optical interferometry using highly entangled field states such as the so-called N00N states, and states obtained by injecting twin Fock states into a beam splitter. With such states and with the performance of parity measurements on one of the output beams of the interferometer, one can breach the standard quantum limit, or shot-noise limit, of sensitivity down to the Heisenberg limit, the greatest degree of phase sensitivity allowed by quantum mechanics for linear phase shifts. Heisenberg limit sensitivities are expected to eventually play an important role in attempts to detect gravitational waves in interferometric detection systems such as LIGO and VIRGO.     

Super-resolution and super-sensitivity of entangled squeezed vacuum state using optimal detection strategy

Interference metrology is a method for achieving high precision detection by phase estimation. The phase sensitivity of a traditional interferometer is subject to the standard quantum limit, while its resolution is constrained by the Rayleigh diffraction limit. The resolution and sensitivity of phase measurement can be enhanced by using quantum metrology. We propose a quantum interference metrology scheme using the entangled squeezed vacuum state, which is obtained using the magic beam splitter, expressed as |ψ〉=(|ξ〉|0〉+|0〉|ξ〉)/(2+2/coshr)~(1/2), such as the N00 N state. We derive the phase sensitivity and the resolution of the system with Z detection, project detection, and parity detection. By simulation and analysis, we determine that parity detection is an optimal detection method, which can break through the Rayleigh diffraction limit and the standard quantum limit.     

Enhanced Phase Estimation in Parity-Detection-Based Mach–Zehnder Interferometer using Non-Gaussian Two-Mode Squeezed Thermal Input State

While the quantum metrological advantages of performing non-Gaussian operations on two-mode squeezed vacuum (TMSV) states have been extensively explored, similar studies in the context of two-mode squeezed thermal (TMST) states are severely lacking. This paper explores the potential advantages of performing non-Gaussian operations on TMST state for phase estimation using parity detection-based Mach–Zehnder interferometry and compares it with the TMSV case. To this end, a realistic photon subtraction, addition, and catalysis model is considered. A unified Wigner function of the photon subtracted, photon added, and photon catalyzed TMST state is derived, which is used to obtain the expression for the phase sensitivity. The results show that performing non-Gaussian operations on TMST states can enhance the phase sensitivity for significant squeezing and transmissivity parameter ranges. Because of the probabilistic nature of these operations, it is of utmost importance to consider their success probability. When the success probability is considered, the photon catalysis operation performed using a high transmissivity beam splitter is the optimal non-Gaussian operation. This contrasts with the TMSV case, where photon addition is observed as the most optimal. Further, the derived Wigner function of the non-Gaussian TMST states will be useful for state characterization and various quantum protocols.     

A scheme for Sagnac-effect quantum enhancement with Fock state light input

Sagnac effect enhancement can improve optical gyro precision. For a certain input intensity, we suggest that the other input port of beam splitter(BS) should be fed with some quantum light to break through shot noise limit(SNL) to improve Sagnac effect without increasing radiation-pressure noise(NRP). We design a Sagnac effect quantum enhancement criterion(SQEC) to judge whether some quantum light can enhance Sagnac effect and present a Sagnac effect enhancement scheme that utilizing Fock state light and parity measurement technique to extract the output phase. The results of the theoretical analysis show that the maximum sensitivity can be reached at θ = 0, and the phase precision can break through SNL and even achieve Heisenberg limit(HL). When the Fock state average photon number n is far less than coherent state, the minimum measurable angular rate is improved with (2n+1)~(1/2) times, which can deduce shot noise and increase NRP little.     

Synthesis and analysis of entangled photonic qubits in spatial-parity space

We present the novel embodiment of a photonic qubit that makes use of one continuous spatial degree of freedom of a single photon and relies on the parity of the photon's transverse spatial distribution. Using optical spontaneous parametric down-conversion to produce photon pairs, we demonstrate the controlled generation of entangled-photon states in this new space. Specifically, two Bell states, and a continuum of their superpositions, are generated by simple manipulation of a classical parameter, the optical-pump spatial parity, and not by manipulation of the entangled photons themselves. An interferometric device, isomorphic in action to a polarizing beam splitter, projects the spatial-parity states onto an even-odd basis. This new physical realization of photonic qubits could be used as a foundation for future experiments in quantum information processing.     

Quantum non-demolition measurement of photon number using weak nonlinearities

We propose an alternative method for the quantum non-demolition measurement of photon numbers wherein weak cross-Kerr nonlinearities are to be used. The usual approach to quantum non-demolition measurements of quantum number involves encoding the photon number, through a cross-Kerr interaction, into a phase shift of a probe coherent state which is then detected through balanced homodyning. Weak nonlinearities produce small phase shifts which are difficult to detect and distinguish. In the method we propose, unbalanced homodyning acts as a displacement operator on the probe beam coherent state such that the cross-Kerr interaction encodes the photon number into the amplitude of a new coherent state. The value of the photon number can be determined by inefficient photon counting on the new coherent state. Our proposed method requires fewer resources than does the usual approach.     

Enhancement of electron spin coherence by optical preparation of nuclear spins

We study a large ensemble of nuclear spins interacting with a single electron spin in a quantum dot under optical excitation and photon detection. At the two-photon resonance between the two electron-spin states, the detection of light scattering from the intermediate exciton state acts as a weak quantum measurement of the effective magnetic (Overhauser) field due to the nuclear spins. In a coherent population trapping state without light scattering, the nuclear state is projected into an eigenstate of the Overhauser field operator, and electron decoherence due to nuclear spins is suppressed: We show that this limit can be approached by adapting the driving frequencies when a photon is detected. We use a Lindblad equation to describe the driven system under photon emission and detection. Numerically, we find an increase of the electron coherence time from 5 to 500 ns after a preparation time of 10 micros.     

Experimental observation of quantum Talbot effects

We report the first experimental observation of quantum Talbot effects with single photons and entangled photon pairs. Both the first- and second-order quantum Talbot self-images are observed experimentally. They exhibit unique properties, which are different from those produced by coherent and incoherent classical light sources. In particular, our experiments show that the revival distance of two-photon Talbot imaging is twice the usual classical Talbot length and there is no net improvement in the resolution, due to the near-field effect of Fresnel diffraction, which is different from the case of previous proof-of-principle quantum lithography experiments in the far field.     

Generating a Four-qubit Photon-Number Cluster State via Cross-Kerr Medium

A scheme is proposed for generating a photon-number entangled cluster state among four modes. The scheme only uses Kerr medium and homodyne measurement on probe coherent light fields, which can be efficiently made in quantum optical laboratories. The photon in the signal mode is prepared in a superposition state of the vacuum state and one-photon state while the probe beam is initially set in a intense coherent state superposition. It is shown that under certain conditions, the four-photon cluster state can be generated effectively with high success probability and homodyne detection required only once, and the scheme is feasible by current experimental technology.