Linear Optical Implementation of Quantum Clock Synchronization Algorithm

We propose optical implementation for the quantum clock synchronization （QCS） algorithm by using only linear optical elements. Our method is based on the single photon representation of qubits. Two kinds of linear optical realization schemes, i.e,, the location-plus-polarization-qubit scheme and the all-location-qubit scheme, are proposed, respectively. Linear optical realizations of three-qubit and four-qubit QCS algorithm are explicitly presented.     

能同时产生不同频率脉冲信号的双波长主动锁模光纤激光器

用两只光纤光栅（FBG）作波长选择器件，实现了一种能同时输出两个不同重复频率的光脉冲序列的双波长主动锁模环形腔光纤激光器。通过调速外加调制信号的频率，使其中一个波长工作在谐波锁模状态，另一个波长工作在有理数谐波锁模状态，实验在2GHz和2.5GHz的调制频率下都成功地获得了双波长且重复频率不同的光脉冲序列，脉冲宽度分别约为60ps和45ps。     

Broadband Ultrashort Pulses in Passively Mode-Locked Fiber Lasers

Optics and Spectroscopy - Generation of ultrashort pulses with an ultimately broad spectrum in fiber lasers is investigated by using numerical modeling and analytical calculations. It is...     

Ground-State Properties of Superfluid Fermi Gas in Fourier-Synthesized Optical Lattices

By employing the balance condition between the lattice potential and the interatomic interaction, we study the ground state solutions of superfluid Fermi gases in Fourier-synthesized （FS） optical lattices. The average energy of the ground state, the atoms number, and the atom density distribution of the Fermi system are analytically derived along the Bose–Einstein condensation （BEC） side to the Bardeen–Cooper–Schrieffer （BCS） side. We analyze the properties of ground state solutions at both the BEC limit and unitarity in FS optical lattices. It is found that the relative phase α between the two lattice harmonics impacts greatly on the properties of the ground state of the superfluid Fermi gas. Especially in the BCS limit, when α=π/2, the average energy presents an exponential form with the increase of the potential depth of the lattice harmonics v2. Meanwhile, there exits a minimal value. Moreover, due to the Fermi pressure, the atom density distribution at unitarity is more outstretched than that in the BEC limit. The average energy at unitarity is apparently larger than that in the BEC limit. The properties of the ground state solution exhibit very different behaviors when the system transits from the BEC side to the BCS side.     

利用单光源光电振荡器实现多波长光脉冲与电时钟信号产生

提出了一种利用单光源光电振荡器(OEO)结构实现多波长光脉冲输出的方案.通过一个直调光源和光谱切片技术在OEO腔内可以产生不同中心波长的光脉冲和电时钟信号.腔内多个波跃通道自然形成的多环路结构可以有效地抑制信号边模.在5 GHz频率的实验演示中,该系统产生了脉宽约10 ps,抖动1 ps的单波长脉冲、20 GHz(4×5 GHz)的时分复用脉冲与波/时分复用脉冲.所得到电时钟信号的相位噪声在频偏10 kHz处为-113 dBc/Hz,边模抑制比为100 dBc/HZ.     

稳态锁模产生4ps激光脉冲

首次利用ＧａＡｓ光电导开关，控制Ｎｄ：ＹＬＦ激光器腔内Ｑ值，实现稳态锁模，获得脉宽和能量稳定性极高的４ｐｓ激光脉冲。     

基于SOA-DI的全光自同步时钟提取装置的噪音分析

通过建立等效噪音源模型分析了SOA的ASE噪音对基于SOA—DI的全光自同步时钟提取装置性能的影响，给出了数学模型并进行了数值理论仿真．仿真结果表明，与不考虑噪音的情况相比，其它参量一定时，随着DI延迟时间减小到某一定值，装置的消光比（CR）不再增加而是急剧减小．在仿真结果基础上，通过设计不同参量值可以抵消噪音的影响，优化系统性能．     

从引力波探测中的压缩光到光原子钟

2020年度“墨子量子奖”授予量子精密测量领域,获奖科学家是Carlton Caves,香取秀俊和叶军.香取秀俊和叶军又获得2021年基础物理学突破奖.对于引力波探测中的量子噪声,Caves分析了海森堡不确定关系所带来的测量精度极限,并且提出用压缩光来克服这个极限.这个方法已经被探测引力波的激光干涉仪实际采用.原子钟基于原子中电子改变能量状态时,发射或吸收的电磁波,提供了最精确的时间和频率标准.与基于微波的原子钟相比.光原子钟,特别是光晶格上的大量原子,可以达到更好的精度.叶军的研究组将约1万个锶原子放在3维光晶格中,实现光原子钟,相对精度达到2.5×10^-19.香取秀俊的研究组搭建的两个可移动光原子钟,精度达到了5×10^-18,并用来测量了引力红移,达到地面测量的最好精度.     

Effect of Stimulated Raman Scattering on Spectral Characteristics of Ultranarrow Pulses in a Mode-Locked Solid-State Laser

On the basis of numerical modeling, it is shown that the effect of the higher-order group-velocity dispersion is unable to account for the noticeable Stokes displacement of the generation spectrum in a LiSGaF laser with mode-locking due to self-focusing. The results of calculations indicate the determining influence of stimulated Raman scattering on the spectral characteristics of femtosecond pulses.     

Electrical Wavelength Switching of Ultrashort Pulses in a Mode-Locked Er-Doped Fiber Ring Laser with Fiber Gratings

Electrical wavelength switching of picosecond pulses was demonstrated in an actively mode-locked Er-doped fiber ring laser with fiber gratings by changing the electrical driving frequency of the modulator. Laser pulses switchable between two wavelengths spaced from 0.5 to 18 nm apart were achieved. The switching speed between the two wavelengths was of the order of several hundred kilohertz.     

Qubit-Based Clock Synchronization for QKD Systems Using a Bayesian Approach

Quantum key distribution (QKD) systems provide a method for two users to exchange a provably secure key. Synchronizing the users’ clocks is an essential step before a secure key can be distilled. Qubit-based synchronization protocols directly use the transmitted quantum states to achieve synchronization and thus avoid the need for additional classical synchronization hardware. Previous qubit-based synchronization protocols sacrifice secure key either directly or indirectly, and all known qubit-based synchronization protocols do not efficiently use all publicly available information published by the users. Here, we introduce a Bayesian probabilistic algorithm that incorporates all published information to efficiently find the clock offset without sacrificing any secure key. Additionally, the output of the algorithm is a probability, which allows us to quantify our confidence in the synchronization. For demonstration purposes, we present a model system with accompanying simulations of an efficient three-state BB84 prepare-and-measure protocol with decoy states. We use our algorithm to exploit the correlations between Alice’s published basis and mean photon number choices and Bob’s measurement outcomes to probabilistically determine the most likely clock offset. We find that we can achieve a 95 percent synchronization confidence in only 4140 communication bin widths, meaning we can tolerate clock drift approaching 1 part in 4140 in this example when simulating this system with a dark count probability per communication bin width of 8×10−4 and a received mean photon number of 0.01.     

基于EPL的分布式时钟同步方法

工业以太网协议Ethernet POWERLINK(EPL)分布式站点的时钟同步方法并不能在实时运行过程中保持很高的同步精度,无法满足特定环境下的控制要求。研究了工业以太网协议EPL的两种时钟同步机制,通过数理计算分析了时钟同步误差产生的原因,针对误差较大的缺点,提出了减小误差的方法。通过迭代计算消除了主从站同步报文往返的路径延迟,并设计基于现场可编程门阵列(FPGA)的集线器(Hub)用于EPL菊花链网络拓扑结构,有效地克服了时钟同步报文往返传输延时不一致的缺点,测试结果表明新方法明显优于协议自身的时钟同步方法,对于实现基于EPL的高精度分布式时钟同步网络具有重要意义。     

Note on Clock Synchronization and Edwards Transformations

Edwards transformations relating inertial frames with arbitrary clock synchronization are reviewed and put in more general setting. Their group-theoretical context is described.     

Generation of 170-fs Laser Pulses at 1053nm by a Passively Mode-Locked Yb:YAG Laser

A novel method is developed to obtain 1.05μm laser operation with a Yb：YAG laser. By using a Yb：YAG crystal with proper length and doping concentration, a femtosecond Yb： YAG laser is realized at the central wavelength of 1053nm. The measured pulse duration and spectral bandwidth （FWHM） are 170fs and 7nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180mW is achieved.     

光学频率标准与光钟的实现

综述了时间频率标准的发展过程.对构成光学频率标准的四个要素,即激光冷却、激光稳频、离子捕陷和光学频率梳进行了系统的介绍.详细描述了光钟的原理与系统构成,并对光学频率标准与光钟的应用前景进行了展望.     

法布里—珀罗标准具滤波器对超短光脉冲的时间响应

系统地研究了法布里－珀罗标准具滤波器对超短光脉冲的时间响应，由于光在标准具内多次反射所引起的干涉效应，发现输出的光脉冲包含了一连串的次脉冲，这些次脉冲的时间间隔等于光单次通过标准具的时间，在一定条件下，这些次脉冲简并在一起产生一展宽的输出光脉冲，并且输出和输入光脉冲峰值的时间间隔并不等于光单次通过标准具的时间，并得出了在考虑色散和啁啾情况下输出次脉冲的表达式。     

法布里－珀罗标准具滤波器对超短光脉冲的时间响应

系统地研究了法布里－珀罗标准具滤波器对超短光脉冲的时间响应。由于光在标准具内多次反射所引起的干涉效应，发现输出的光脉冲包含了一连串的次脉冲，这些次脉冲的时间间隔等于光单次通过标准具的时间。在一定条件下，这些次脉冲简并在一起产生一展宽的输出光脉冲，并且输出和输入光脉冲峰值的时间间隔并不等于光单次通过标准具的时间。并得出了在考虑色散和啁啾情况下输出次脉冲的表达式。     

Effects of Quantum Noise on Quantum Clock Synchronization

In laboratory environment, the channel apparatus will generate particular dominant quantum noise. The noise then will give rise to some errors during synchronization. In this work, the accuracies of one qubit transport protocol and entangled states transport protocol in the presence of noise have been studied. With the help of three important and familiar noise models, the quantum noise will degrade the accuracy has been proved. Due to the influence of quantum noise, the accuracy of entangled qubits decrease faster than that of one qubit. The entangled states will improve the accuracy in noise-free channel, and will degrade the accuracy in noise channel.     

Wideband All-Polarization-Maintaining Yb-Doped Mode-Locked Fiber Laser Using a Nonlinear Optical Loop Mirror

We report on a wide-band and stable mode-locked all-polarization-maintaining fiber iaser configuration using a noniinear optical loop mirror.The central wavelength of the laser is 1080.14 nm and the 3dB bandwidth is 20.29 nm.The repetition rate of the pulse is 3.28 MHz and the pulse width is 848 ps.By tuning the pump power,which is centered at 980 nm,from 300 mW to 380 mW,we obtain a linearly changed output power from 6mW to 7.12 mW.The all-polarization-maintaining fiber configuration is fundamental to the stability of the output power.