Optical lattice clocks for fundamental physics and redefinition of the second

原子钟是最精确的计时装置。它们的工作原理是稳定一些电磁辐射的频率，使其与原子能级转换的频率相匹配。基于铯133原子的时钟在国际单位制中提供了秒的定义，并用于实现世界协调时间和卫星导航等需要准确计时的技术。光学钟的工作原理与原子钟相同，不同之处在于它们使用的是频率更高的光域中的辐射。随之而来的更高的灵敏度意味着原子需要非常小心地冷却到英国的温度，光学晶格钟也使用光学光来捕获处于低动能状态的原子。这些时钟目前正在开发中，以变得更可靠和更坚固，但已经显示出比普通原子钟更高的精度。这表明，将需要对秒有一个新的定义，以便可以使用更精确的光学钟来实现秒。这种提高精度的另一个令人感兴趣的方面是，有可能进行非常精确的大地测量，并研究难以捉摸的现象，如基本常量和暗物质的变化。该项目的目标是通过展示具有更高稳定性的时钟运行，以及通过以更高精度测量不同物种(即锶和Yb离子)的时钟的频率比，来为重新定义第二个和基础物理研究做出贡献。研究的新颖性来自于在激光稳定过程中采用的减少噪声的新技术。时钟性能的极限将表现为理论考虑、新开发的计算机模拟和实验的混合，以研究单个时钟的最佳操作参数，以及组合两个时钟以产生比单个时钟可能产生的更稳定的结果的复合架构。这些解决方案将建议改变时钟(S)的操作方式，而不是改变实验硬件。这项工作将在国家物理实验室进行，这是英国的计量研究所，专注于生产测量和校准标准，还将通过国际测量活动让欧洲、美洲和亚洲的其他计量机构参与进来。

Atomic clocks are the most precise timekeeping devices. They work by stabilizing the frequency of some electromagnetic radiation so that it matches the frequency of an atomic energy level transition. Clocks based on Caesium 133 atoms provide the definition of the second in the international system of units and are used to realise Universal Coordinated Time and in technologies that require accurate timekeeping such as satellite navigation. Optical clocks work on the same principle as atomic clocks with the difference that they use radiation in the optical domain which has a higher frequency. The increased sensitivity that comes with this means that atoms need to be very carefully cooled down to uK temperatures, and optical lattice clocks also use optical light to trap atoms in a low kinetic energy state. These clocks are currently under development to become more reliable and robust but have already demonstrated higher precision than normal atomic clocks. This suggests that a new definition of the second will be needed so that the realisation of the second can be done using the more precise optical clocks. Another aspect of this increased precision that generates interest is the possibility of performing very accurate geodesy and investigating elusive phenomena such as variations in fundamental constants and dark matter. The objectives of this project are to contribute to the effort to redefine the second and to the fundamental Physics research by demonstrating clock operation with improved stability and by performing measurements of frequency ratios of clocks with different species (namely Strontium and Ytterbium ion) with enhanced precision.The novelty of the research stems from the new techniques employed to reduce the noise in the laser stabilization process. The limits of clock performance will be characterised by a mixture of theoretical considerations, newly developed computer simulations and experiments to investigate optimal operating parameters for an individual clock as well as composite architectures which combine two clocks to produce a more stable result than what is possible with a single clock. The solutions will propose changes in how the clock(s) is operated rather than changes to the experimental hardware.This work will be conducted at the National Physical Laboratory which is the metrology institute for the UK focusing on producing standards for measurement and calibration, and will also involve other metrology institutes in Europe, America and Asia through international measurement campaigns.