Review of chip-scale atomic clocks based on coherent population trapping

Research on chip-scale atomic clocks （CSACs） based on coherent population trapping （CPT） is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance＇s collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.     

相干布居数拍频信号与基态超精细子能级相干性关系的研究

相干布居数拍频(coherent population beating, CPB)现象, 产生于一个Λ型三能级原子系统中, 当双色相干激光场的频率差和两基态能级频率间隔近失谐的时候, 原子在激发态能级上的布居数会产生一个弛豫振荡, 且振荡频率等于失谐量. 当将此现象运用于原子标准频率的提取时, CPB频标的稳定度与CPB信号的幅度及信噪比直接相关. 本文理论推导了描述CPB 现象的表达式, 数值模拟并实验研究了⁸⁷Rb基态超精细子能级的相干性对CPB信号的影响, 通过控制与基态子能级共振相干激光场的抽运时间来控制能级的相干程度, 观测不同相干程度对CPB信号质量的影响. 研究结果表明CPB信号振荡的幅度与基态子能级相干程度成正比关系. 要改善CPB信号信噪比、提高原子频标稳定度, 建立、提高和保持基态超精细能级的相干性是关键. 本文还讨论了CPB现象用于弱磁场测量及其他方面应用的可行性.     

Coherent effects in a three-photon CPT process of Ca+

Linewidth narrowing and other quantum coherent effects based on three-photon coherent population trapping (CPT) in Ca⁺ ions are investigated. If the propagation directions of the three lasers obey the phase matching condition, the dark linewidth resulting from the CPT can be very narrow, and it can be controlled by adjusting the parameters of the lasers.     

InGaN薄膜中电子自旋偏振弛豫的时间分辨吸收光谱研究

采用飞秒时间分辨圆偏振光抽运-探测光谱对In_01Ga_09N薄膜的电子自旋注入和弛豫进行了研究.获得初始自旋偏振度约为02,此结果支持在圆偏振光激发下,重、轻空穴带的跃迁强度比为3∶1,而不支持1∶1或1∶094的观点同时获得自旋偏振弛豫时间为490±70ps,定性分析了自旋弛豫机理,认为BAP机理是电子自旋弛豫的主要机理.关键词：电子自旋InGaN自旋极化自旋弛豫     

Nuclear Spin Maser Oscillation of 129Xe by Means of Optical-Detection Feedback

We have developed the nuclear spin maser oscillating at a low frequency of 34 Hz with highly polarized nuclear spins of the noble gas element ¹²⁹Xe. The system is advantageous for detecting a small frequency shift of the nuclear spin precession. We are thus planning to apply this system to the search for an atomic electric dipole moment of ¹²⁹Xe. We here report the development of the system and its performance.     

Photoionization properties of an atom with two autoionizing states

We have investigated the photoionization properties of an atom with a ladder coupling scheme involving two autoionizing states coupled to each other.The effects of the coherent coupling between two autoionizing states and between the low-lying autoionizing state and the continuum on the ionization yield are discussed.The conditions leading to atomic coherent population trapping and the coherent population trapping states are given explicitly.     

Atomic Coherent Trapping and Properties of Trapped Atom

Based on the theory of velocity-selective coherent population trapping, we investigate an atom-laser system where a pair of counterpropagating laser fields interact with a three-level atom. The influence of the parametric condition on the properties of the system such as velocity at which the atom is selected to be trapped, time needed for finishing the coherent trapping process, and possible electromagnetically induced transparency of an altrocold atomic medium, etc., is studied.     

芯片原子钟相干布居囚禁谱线特性研究

通过微型原子蒸汽室产生质量满足要求的相干布居囚禁(CPT)信号是实现芯片原子钟的关键之一.本实验通过对光源实施频率调制和对光场与⁸⁷Rb原子作用产生的信号作相敏解调获得高信噪比的CPT微分谱线, 利用CPT微分谱线研究了CPT信号随工作参数变化的规律以及信号质量对原子钟频率稳定度的影响, 所获研究结果与理论模型预期相符合, 实验结果为芯片原子钟推荐了最佳工作参数.实验所采用的方法利用芯片原子钟自身的资源就可以实施, 因此为芯片原子钟开展性能研究和实施工作参数优化提供了实用的手段.     

Atomic Coherent Trapping and Properties of Trapped Atom

Based on the theory of velocity-selective coherent population trapping, we investigate an atom-laser system where a pair of counterpropagating laser fields interact with a three-level atom. The influence of the parametric condition on the properties of the system such as velocity at which the atom is selected to be trapped, time needed for finishing the coherent trapping process, and possible electromagnetically induced transparency of an altrocold atomic medium,etc., is studied.     

准一维半导体量子点中电偶极自旋共振的物理机理

半导体量子点中的电子自旋具有较长相干时间以及可扩展性的特点, 在近十几年来引起了人们的广泛兴趣. 人们常常利用电子自旋共振技术来对单个自旋进行操纵. 这样不但需要一个静磁场来使电子产生赛曼劈裂, 同时还需要一个与之垂直的局域振荡磁场. 但是, 在实验上产生足够强且具有固定频率的局域磁场是比较困难的. 后来人们发现, 局域的振荡电场也可以操纵单个电子自旋, 也就是所谓的电偶极自旋共振. 众所周知, 自旋只有自旋磁矩, 不会与电场有任何直接的相互作用. 所以, 电偶极自旋共振的发生必须依赖于某些媒质. 这些媒质包括：量子点材料中的自旋轨道耦合作用, 量子点中的局域磁场梯度, 以及量子点中电子自旋与核自旋的超精细相互作用. 这些媒质能诱导出自旋与电场之间间接的相互作用, 从而外电场操纵单个电子自旋得以实现. 本文总结归纳了目前半导体量子点系统中发生电偶极自旋共振的三种主要物理机理.     

电阻式核磁共振测量的最新进展

电阻式核磁共振(RDNMR)测量是1988年由德国马普所的von Klitzing研究小组针对GaAs二维电子气中少量核自旋的探测而提出的一种具有超高灵敏度的实验技术. 目前, RDNMR已经成为研究单层或双层GaAs二维电子气核自旋和电子自旋特性的重要手段. 由于为实现电阻式核磁共振测量所建立的动态核极化方法强烈依赖于GaAs特有的材料属性, 至今这一技术一直没有扩展应用到其他半导体低维系统中. 最近,本研究小组发展了一种动态核极化新方法,成功实现了对典型窄带半导体锑化铟(InSb) 二维电子气的电阻式核磁共振测量.本文在介绍电阻式核磁共振测量工作原理及已建立的典型动态核极化方法的基础上,着重讨论所提出的动态核极化新方法的机理、 实验结果以及对今后研究的展望.     

Passive magnetic shielded spin polarized electron source with optical electron polarimeter

A new GaAs(100) spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5×10^-7,T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95cm distance through an 1mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8\pm3.5% measured with a He optical polarimeter.     

Spin concentration in a possible ESR dosimeter: An electron spin echo study on X-irradiated ammonium tartrate

Several single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 10(18)-10(19) spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described.     

Manifestation of the Dynamics of Spin Temperature in EPR in the Absence of Interaction with the Lattice

Within the framework of the concept of spin temperature in electron paramagnetic resonance (EPR) in the absence of the interaction with the lattice, the time dependence for spin temperatures of the Zeeman subsystem and dipole–dipole reservoir is theoretically investigated in both high- and low-temperature approximations. It is shown that the gain can be produced in the system by switching the frequency of the saturating field. The gain in the system as a function of the detuning of the frequency of the saturating field is investigated in a high-temperature approximation. In the presence of a test field in a high-temperature approximation, the possibility of determining the magnitude of a local magnetic field, which is associated with the time of transverse relaxation of the system, is discussed.     

Transient responses of transparency in a far-off resonant atomic system

Transient coherent oscillations in a closed Λ system under far-off resonant Raman fields were investigated theoretically. It has been found that the coherent superposition of the ground states can be formed due to the absorption even for initial maximal mixed ground states. The absorption oscillates with a period depending on the two-photon detuning when the system is initially in a transparent state and the two-photon Raman detuning is suddenly changed. The amplitude of the absorption decays with the decay rate of the ground states, which is different from the case when the lasers are applied resonantly. These transient coherent oscillations can be used to measure the relaxation rate of the ground states.     

一个特殊模型中的相干布居俘获

外场作用下,对称双势阱中将发生相干布居俘获现象. 在氨分子模型中,当分子初始处在较低的本征态时,在一定的条件下激发态上将没有粒子数布居,外加光场强烈地使较低的双重态耦合在一起,且粒子数布居总保持为1,尽管此时外场与|2〉→|3〉接近共振. 这是一般模型所不能得到的结论.关键词：相干布居俘获Ξ型三能级系统双势阱