光子计数激光测距技术研究

光子计数激光雷达采用了灵敏度极高的单光子探测器,能够将激光雷达系统的灵敏度提高2—3个数量级,具有极大的发展潜力和技术优势。介绍和分析了光子计数激光测距技术的基本原理和优点。设计了光子计数激光雷达实验系统,采用盖革模式的雪崩二极管(Geiger-mode APD),开展了测距验证实验。实验结果表明,采用光子计数激光测距能够在单光子灵敏度和强噪声背景条件下,获取目标的距离信息,距离测量精度达到6.23 cm。     

用强场激光探测轴子实验中的光子静质量效应

在重电磁场理论背景下,探讨了用激光通过强磁场探测轴子的高精度实验中光子静质量效应的大小和影响,并与调制扭秤实验给出的光子静质量限作比较.结果表明:此类实验中光子静质量效应对轴子质量限的影响很小;实验给出可能的光子静质量限mr＜1×10-3eV,精度远小于调制扭秤实验给出的光子静质量限精度,扭秤实验仍是目前检测光子静质量的有效手段.     

国内新闻

实现高精度量子相位测量在测量时间等基础物理量时,其测量精度可超过受噪声所限的标准量子极限(即噪声极限),但却无法逼近海森堡极限。中国科技大学中国科学院量子信息重点实验室孙方稳和柳必恒在郭光灿院士指导下,利用双模光子数态和独创的多光子投影测量方法,避免了光子损耗,实现了高精度的量子相位测量,冲破了"标准量子极限",并十分接实现高精度量子相位测量在测量时间等基础物理量时,其测量精度可超过受噪声所限的标准量子极限(即噪声极限),但却无法逼近海森堡极限。     

基于多光子叠加态的交叉相位调制耦合参数测量

继纠缠之后,粒子间相互作用已成为量子增强的重要资源.在不利用纠缠资源的前提下,已有研究工作利用单光子叠加态与相干态的相互作用实现了精度为海森堡极限的参数测量,然而海森堡极限并不是这个相互作用模型的测量精度极限.为了得到更高的测量精度,将单光子叠加态替换为多光子叠加态,在弱测量框架下对信号光量子态进行后选择与量子态筛选.将单光子叠加态替换为多光子叠加态,能为测量结果带来全方位提升.提出基于多光子叠加态的交叉相位调制耦合参数测量的物理方案,该物理方案具有搭建难度低及操作简单的优点.     

基于光子技术的实时频率测量方法

研究了一种基于光子技术的实时频率测量方法,该方法利用两个级联强度调制器构成光子混频结构.通过理论分析与模拟仿真,设计了光通道与射频通道延时差,以优化测量带宽,同时保证测量精度.由于测量系统对微波信号实现混频后,输出的直流光功率与频率存在对应关系,利用光功率计对直流光功率进行监测,便可实现实时频率测量.该系统未采用光电探测器,极大地降低了系统成本.实验结果表明,在1~6GHz频率下,测量误差低于±0.12GHz.     

物理光学的若干进展

就物理光学方面的一系列理论和实验研究，如GoosHnchen位移、FTIR现象、负折射率、太赫超光速实验、光子静质量测量等做了评述和讨论。指出近年来的研究显示了消失波现象的重要性，例如消失波可造成超光速传播，且常有新方法和新测量结果；介绍了物理光学在相关领域的技术创新和应用实例；讨论了光子有静止质量的可能性及光频标准和光频测量的历史和新的进展     

基于量子纠缠对的二阶相关星地时钟同步研究

在卫星导航系统中,常用的时间同步方法可以提供纳s级同步精度,为突破经典无线电理论的测量精度而利用纠缠光子对的量子测量方法可提供fs级测量精度。基于量子光学的二阶相关函数定义,对自发参量下转换过程产生量子纠缠光子对的二阶相关函数在晶体范围内进行柱面积分,代入波矢量的一阶展开,积分结果得到二阶相关函数与测量时间差的关系。基于二阶相关函数的时间相关性,提出一种星地时钟同步测量方案。仿真表明:在理想情况下二阶相关函数反映时间精度达70fs,文中设计方案同步测量精度可达140fs。     

量子延迟选择实验中的因果性

对光子波粒二象性的探讨依然是物理学中基础性研究的重要内容.根据几率理论和波函数的几率解释对一个量子延迟实验进行了分析研究,结果表明:检验光子处于水平偏振态与处于垂直偏振态的几率都是1/2,与测量确认光子的设备的状态无关;检验光子是表现为粒子行为还是表现为波动行为完全取决于它的偏振状态,与确认光子是否被探测无关;检验光子与确认光子的符合探测几率随着测量确认光子的设备状态的改变而改变,但是不可能通过改变测量确认光子设备的状态把检验光子的波动行为改变为粒子行为.     

光子静止质量与雷达回波延迟

讨论了弯曲时空下,当光子静止质量不为零时引力的时间延迟效应,即光子静止质量对在地球上发射再从行星上反射回来的掠过太阳的雷达回波延迟的影响.计算了当光子静止质量不为零时对原有电磁波运动方程的影响,并将实验所得数据与理论计算数据之间的误差归结为光子静止质量引起,由火星回波延迟的实验数据给出光子静止质量上限为2.2×10-43g.同时讨论了实验中误差的来源,并提出了进一步提高实验精度和获得光子静止质量更高上限的途径.     

单光子计数实验的结果分析

阐述了单光子计数实验原理和光电倍增管、光子计数器等器件的功能,绘制了通过500nm二极管的电流与测量光子数、信噪比的关系曲线,并对实验结果进行了分析。     

光子分类研究及其在核磁共振技术中的应用

通过分析维纳（Ｏ．Ｗｉｅｎｅｒ）驻波实验,认为光子应分为电光子和磁光子．从定性、定量两个方面讨论了电光子和磁光子,分析了磁光子在核磁共振技术及其它现代技术中的应用．     

规则泵情况下激光的光子数分布

利用光子数表象推导了泵噪声被抑制情况下的激光的光子数分布．它表明,在以往利用光子数表象计算光子数分布产生负几率的原因并不在该表象本身,而是因为截断了主方程所造成的．并在不截断主方程的基础上,导出了规则泵及原子自发辐射被抑制的激光系统的光子数分布的特征函数及分布函数．特征函数可被用来很方便地求解光子数分布的各阶矩．这一方法可推广到不完全规则泵和考虑原子自发辐射的情况．     

Experimental realization of freely propagating teleported qubits

Quantum teleportation is central to quantum communication, and plays an important role in a number of quantum computation protocols. Most information-processing applications of quantum teleportation include the subsequent manipulation of the qubit (the teleported photon), so it is highly desirable to have a teleportation procedure resulting in high-quality, freely flying qubits. In our previous teleportation experiment, the teleported qubit had to be detected (and thus destroyed) to verify the success of the procedure. Here we report a teleportation experiment that results in freely propagating individual qubits. The basic idea is to suppress unwanted coincidence detection events by providing the photon to be teleported much less frequently than the auxiliary entangled pair. Therefore, a case of successful teleportation can be identified with high probability without the need actually to detect the teleported photon. The experimental fidelity of our procedure surpasses the theoretical limit required for the implementation of quantum repeaters.     

轻小型光子计数激光测距技术

为实现轻小型光子计数测距仪,利用905nm激光二极管（LD）以及硅基单光子探测器（SPAD）搭建了试验系统,通过外场测距试验研究了905nm激光二极管用于光子计数测距的测距性能。结果表明：905nm激光二极管由于其具有体积小、功率高的特点,同时硅基单光子探测器在905nm波段具有较高的响应率,基于以上两点,通过激光二极管以及小口径的接收望远镜能够实现远距离的光子计数激光测距。可见,激光二极管适合作为轻小型光子计数激光测距仪的光源,降低了系统的体积,有利于提高测距系统的集成度。     

Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics

The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.     

Resolving photon number states in a superconducting circuit

Electromagnetic signals are always composed of photons, although in the circuit domain those signals are carried as voltages and currents on wires, and the discreteness of the photon's energy is usually not evident. However, by coupling a superconducting quantum bit (qubit) to signals on a microwave transmission line, it is possible to construct an integrated circuit in which the presence or absence of even a single photon can have a dramatic effect. Such a system can be described by circuit quantum electrodynamics (QED)-the circuit equivalent of cavity QED, where photons interact with atoms or quantum dots. Previously, circuit QED devices were shown to reach the resonant strong coupling regime, where a single qubit could absorb and re-emit a single photon many times. Here we report a circuit QED experiment in the strong dispersive limit, a new regime where a single photon has a large effect on the qubit without ever being absorbed. The hallmark of this strong dispersive regime is that the qubit transition energy can be resolved into a separate spectral line for each photon number state of the microwave field. The strength of each line is a measure of the probability of finding the corresponding photon number in the cavity. This effect is used to distinguish between coherent and thermal fields, and could be used to create a photon statistics analyser. As no photons are absorbed by this process, it should be possible to generate non-classical states of light by measurement and perform qubit-photon conditional logic, the basis of a logic bus for a quantum computer.     

微波场影响生物体超弱发光的研究

根据F.A.Popp相干理论及有关实验，生物光子的延迟辐射强度时间服从双曲函数分布，通过对蒜瓣在微波作用下超弱发光的研究表明，并非所有生物体的发光曲线都呈双曲衰减，有些生物体的超弱发光呈振荡趋势。考虑到声子和光子的相互作用，并通过实验和计算机模拟验证这一结果。     

光子计数技术用于SEM二次电子信号检测的理论探讨

本重点在分析比较PMT视频放大系统与PMT光子计数系统的噪声源，信噪比及探测灵敏度的基础上，就光子计数技术在扫描电镜（Scanning Electron Microscope，简称SEM）二次电子信号检测中的可能应用进行了初步的理论探讨。分析表明，SEM采用光子计数技术后，信号探测灵敏度可提高一个量级以上，从而在相同的电子枪发射亮度与既定的电子光学系统下，可获得更高的图象分辨率与清晰度。     

与强度有关的多光子过程中单模场的演化性质

重新考察了两类可解的JCM ,进一步讨论了与强度有关的多光子相互作用过程 ,计算了场强度 (粒子数 )的变化 ,位相及熵的变化及场的压缩的演化情况 ,发现在这种情况下场及原子的某些非经典特性得到了充分体现。特别是奇数光子过程中 ,原子或场会在长时间内反复回到纯态 (腔无损耗 ) ,即原子和场的态反复纠缠成混合态后又会彻底解纠缠成为纯态 ,并且强度的依赖使在强场下加速了这种混合 ,使原子的崩塌与复活更为明显和频繁 ,其演化过程与系统的初态的选取有明显的关系。位相的演化则与场的粒子数演化的混乱度相反 (测不准关系 )。     

Quantum jumps of light recording the birth and death of a photon in a cavity

A microscopic quantum system under continuous observation exhibits at random times sudden jumps between its states. The detection of this quantum feature requires a quantum non-demolition (QND) measurement repeated many times during the system's evolution. Whereas quantum jumps of trapped massive particles (electrons, ions or molecules) have been observed, this has proved more challenging for light quanta. Standard photodetectors absorb light and are thus unable to detect the same photon twice. It is therefore necessary to use a transparent counter that can 'see' photons without destroying them. Moreover, the light needs to be stored for durations much longer than the QND detection time. Here we report an experiment in which we fulfil these challenging conditions and observe quantum jumps in the photon number. Microwave photons are stored in a superconducting cavity for times up to half a second, and are repeatedly probed by a stream of non-absorbing atoms. An atom interferometer measures the atomic dipole phase shift induced by the non-resonant cavity field, so that the final atom state reveals directly the presence of a single photon in the cavity. Sequences of hundreds of atoms, highly correlated in the same state, are interrupted by sudden state switchings. These telegraphic signals record the birth, life and death of individual photons. Applying a similar QND procedure to mesoscopic fields with tens of photons should open new perspectives for the exploration of the quantum-to-classical boundary.