用于可搬运锶光钟二级冷却光源的研制

光钟在时间保持、精密测量、暗物质探测等方面有广泛的应用。可搬运光钟研制是光钟的重要方向，它是不同类型光钟比对以及引力红移测量的重要设备。研制用于冷原子制备的可搬运冷却光源是实现可搬运光钟研制的关键。本文主要介绍了可搬运锶光钟二级冷却光源的研制。首先，通过Pound-Drever-Hall稳频技术将半导体激光器锁定在超稳腔上，实现了用于锶光钟二级冷却的689 nm窄线宽稳频光源，其线宽优于263 Hz，频率秒稳定度优于1.56×10^-14。另外，利用注入锁定技术制备了两台同等性能的光源，分别用作二级冷却阶段的俘获光和匀化光。整个光学系统集成在一个0.56 m²的光学面包板，通过光纤与真空系统耦合，整体可搬运。利用该稳频光源，实验上制备了数目为2×10⁶，温度为5.3μK的二级冷却原子团，这为下一步进行光晶格原子装载和钟跃迁谱探测奠定了基础。     

小型化锶光钟物理系统的研制

光钟物理系统的小型化是制约可搬运光钟及空间冷原子光钟发展的重要因素.主要介绍了小型化锶原子光钟物理系统的研制实验.采用真空腔内置反亥姆霍兹线圈,构建一个小电流、低功耗及小体积的磁光阱.实验中测得真空线圈通电电流仅为2 A时,磁光阱中心区域轴向磁场梯度可达到43 Gs/cm,完全满足锶原子多普勒冷却与俘获对磁场梯度的要求.目前已经成功将锶原子光钟物理系统体积缩小至60 cm×20 cm×15 cm,约为实验室原锶光钟物理系统体积的1/10,并且实现了锶原子的一级冷却,测得俘获区冷原子团的直径为1.5 mm,温度约为10.6 mK.锶同位素~(88)Sr和~(87)Sr的冷原子数目分别为1.6×10~6和1.5×10~5.重抽运激光707和679 nm的加入,消除了冷原子在~3P_2和~3P_0两能态上的堆积,最终可将冷原子数目提高5倍以上.     

可搬运锶光晶格钟系统不确定度的评估

可搬运光学原子钟在科学研究和工程应用中具有重要意义.本文测量了可搬运87Sr光晶格钟系统的主要频移,包括黑体辐射频移、碰撞频移、晶格光交流斯塔克频移、二阶塞曼频移等.首先实验上测量了磁光阱腔体表面的温度分布,分析了不同热源对原子团的影响,得到黑体辐射总的相对频移修正量为50.4×10^-16.相对不确定度为5.1×10^-17.然后利用分时自比对方法,评估了碰撞频移、晶格光交流斯塔克频移和二阶塞曼频移.结果表明,由黑体辐射引起的频移量最大,晶格光交流斯塔克频移的不确定度最大,系统总的相对频移修正量为58.8×10^-16,总不确定度为2.3×10^-16.该工作为可搬运87Sr光晶格钟之后的性能提升和应用提供了条件.     

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.     

光钟

时间标准的研究在人类生活和科学探索中有着举足轻重的地位。文章简要介绍了时间的基本单位＂秒＂定义的几次重要发展与变迁,重点介绍了光钟的工作原理、关键部件、研究进展和光钟对＂秒＂定义未来发展的重要性。     

光晶格原子钟研究进展

经过近20年的发展,基于光频跃迁的光晶格原子钟展示了优异的频率稳定度和不确定度,是重定义时间单位“秒”的有力候选者之一。随着地面基准光晶格原子钟性能的提升,光晶格原子钟已经成功地走出了实验室,实现了可搬运晶格原子钟并正在研制可在太空中运行的空间光晶格原子钟。本文综述了影响光晶格原子钟稳定度和准确度的关键因素,以及抑制或者消除这些因素的主要技术;并结合国内外的研究成果,综述了地面基准光晶格原子钟、可搬运光晶格原子钟和空间光晶格原子钟的技术特点和研究进展。     

锶原子光晶格钟

进入21世纪以来,锶原子光晶格钟经历了快速的发展,系统频移的不确定度指标已经超越现有的秒定义基准铯原子喷泉钟,进入到10~(-18)量级,体现了人类精密测量能力的最高水平,是精密测量物理的热点研究内容.本综述简要介绍了锶原子光晶格钟的发展水平;详细介绍了锶原子光晶格钟的各个组成部分和关键技术、如何进行精密光谱探测和闭环锁定以及各项系统频移的不确定度评估方法和锶原子跃迁绝对频率测量的方法等;最后简要介绍了锶光钟的应用和未来发展趋势.     

提升原子光钟的精度

正研究者用光谱成像方法降低锶原子光晶格钟的频率偏移,获得原子钟精度的新纪录。当今最精确的原子钟是基于锶、镱和其他碱土(或类似于碱土)原子。这些元素具有超窄的跃迁光频率,从而为时间测量提供了稳定、精确的频率标准。相比于目前用来定义秒的铯原子钟,碱土元素的频率标准比它精确近千倍。在美     

离子光频标的原理和发展

人类对时间的计量历史可以追溯到几千年前,随着科学技术的发展与进步,人类对事件的计量精度也越来越精确。当前,世界上最精确的计时工具为光频标,可以达到百亿年不差一秒的水平。文章回顾了离子光频标的发展过程和当前的研究进展,简要介绍了钙离子光频标和量子逻辑铝离子光频标的原理及进展。     

地球引力背景下的卫星-地面量子时钟同步

正原子钟是迄今为止人类能制造的最精密的设备,精确的定时和授时在导航、卫星定位、相对论效应的实验检测、引力波的探测等多个系统或科学计划中扮演了重要的角色。时钟同步事实上是一个比较经典的课题。对于这一问题,人们最熟悉的是两个经典时钟同步方案:爱因斯坦时钟同步方案和爱丁顿的慢钟搬运方案。现有的卫星定位系统的时钟同步用的是前者,人们利用激光或其他信息载     

Cold atom clocks and their applications in precision measurements

Cold atom clocks have made remarkable progresses in the last two decades and played critical roles in precision measurements. Primary Cs fountain frequency standards have achieved a total uncertainty of a few parts in 1016, and the best optical clock has reached a type B uncertainty below 10-18. Besides applications in the metrology, navigation, etc.,ultra-stable and ultra-accurate atomic clocks have also become powerful tools in the basic scientific investigations. In this paper, we focus on the recent developments in the high-performance cold atomic clocks which can be used as frequency standards to calibrate atomic time scales. The basic principles, performances, and limitations of fountain clocks and optical clocks based on signal trapped ion or neutral atoms are summarized. Their applications in metrology and other areas are briefly introduced.     

冷原子气体的时频测量——光晶格原子钟

基于冷原子气体的时频测量在近20年里快速发展,引起了人们的广泛关注,其典型代表是基于大量中性原子的光晶格原子钟。利用超稳钟激光同时探测囚禁在光晶格里成千上万个冷原子的钟跃迁信号,光晶格原子钟已实现10^-18量级的频率准确度和10^-17量级的秒级稳定度,大幅度提高了时频测量的精度。文章概述了光晶格原子钟的发展历史、工作原理、性能评估及应用前景。     

冷原子气体的时频测量——光晶格原子钟

基于冷原子气体的时频测量在近20年里快速发展,引起了人们的广泛关注,其典型代表是基于大量中性原子的光晶格原子钟。利用超稳钟激光同时探测囚禁在光晶格里成千上万个冷原子的钟跃迁信号,光晶格原子钟已实现10^-18量级的频率准确度和10^-17量级的秒级稳定度,大幅度提高了时频测量的精度。文章概述了光晶格原子钟的发展历史、工作原理、性能评估及应用前景。     

Frequency ratios of Sr,Yb, and Hg based optical lattice clocks and their applications

This article describes the recent progress of optical lattice clocks with neutral strontium (⁸⁷Sr), ytterbium (¹⁷¹Yb) and mercury (¹⁹⁹Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on an Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an optical frequency comb, the ratios of the clock frequencies are determined with uncertainties smaller than possible through absolute frequency measurements. Finally, we describe a synchronous frequency comparison between two Sr-based remote clocks over a distance of 15 km between RIKEN and the University of Tokyo, as a step towards relativistic geodesy.     

光晶格原子钟研究进展

钟跃迁频率在光学频段的光晶格原子钟已经实现了10-19 量级的频率稳定度和10-18 量级的频率不确定度, 在量子频标、 量子模拟和精密测量等领域有着重要的应用. 本文综述了光晶格原子钟的发展历史、 工作原理、 性能评估和应用与展望.     

The Search for Variation of Fundamental Constants with Clocks

In many theories beyond the Standard Model the quantities that we call “fundamental constants” become space‐time dependent, leading to corresponding variation of atomic and molecular spectra and clock frequencies. The extraordinary improvement of the atomic clock precision in the past fifteen years enabled testing the constancy of the fundamental constant at a very high level of precision. Herein, searches for the variation of fundamental constants with clocks are discussed, focusing on recent key results and future proposals, including highly charged ion, molecular, and nuclear clocks. The relevance of the recent searches for oscillatory and transient variation of fundamental constants to the major unexplained phenomena of our Universe, the nature of dark matter, is discussed.     

Clock asynchrony and mass variation

In a world with varying particle masses, clocks become asynchronous and metersticks inconsistent. By combining two or more clocks with different known dependences on mass, we can construct a nearly invariant clock, and measure the rate of mass variation.     

Atomic clocks: A brief history and current status of research in India

Frequency corresponding to the energy difference between designated levels of an atom provides precise reference for making a universally accurate clock. Since the middle of the 20th century till now, there have been tremendous efforts in the field of atomic clocks making time the most accurately measured physical quantity. National Physical Laboratory India (NPLI) is the nation’s timekeeper and is developing an atomic fountain clock which will be a primary frequency standard. The fountain is currently operational and is at the stage of complete frequency evaluation. In this paper, a brief review on atomic time along with some of the recent results from the fountain clock will be discussed.     

Atomic fountains and optical clocks at SYRTE: Status and perspectives

In this article, we report on the work done with the LNE–SYRTE atomic clock ensemble during the last 10 years. We cover the progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second.     

Continuous nondemolition measurement of the Cs clock transition pseudospin

We demonstrate a weak continuous measurement of the pseudospin associated with the clock transition in a sample of Cs atoms. Our scheme uses an optical probe tuned near the D1 transition to measure the sample birefringence, which depends on the component of the collective pseudospin. At certain probe frequencies the differential light shift of the clock states vanishes, and the measurement is nonperturbing. In dense samples the measurement can be used to squeeze the collective clock pseudospin and has the potential to improve the performance of atomic clocks and interferometers.