Frequency-comb-based digital clockwork for next-generation optical clocks

这项提议旨在开发光学时钟装置，即用于从光学时钟读出时间的系统。光学钟使用非常稳定的激光，参考孤立原子或多个原子的跃迁频率来提供非常精细和准确的时间细分。它的精度来自于与通常的射频振荡器相比，光的振荡频率非常高，但这也使得读取时钟变得困难，因为频率对于传统的电子手段来说太高了。由于这些光学钟已经实现了更好的时间测量，并可能很快在时间和频率标准上取代射频原子钟，因此我们开发支持它们的基本技术是非常重要的。*准确测量时间是一个基本的过程，需要广泛的应用，从回答关于我们物理世界的深层次科学问题(搜索引力波，绘制地球和行星的引力场扭曲图，测试我们现在认为的物理常数的可能变化)，到实现精确的全球导航、高效通信系统等非常实际的应用。通常，这些科学和技术努力的精确度的限制与其时钟的性能有关。*为了建造时钟，我们需要一个稳定的、可重复的物理现象(这里指的是锁定在原子跃迁中的激光电磁场的振荡)，还需要计算已经发生的这些振荡的次数的方法。因此，每个光学时钟都需要相称的光学时钟来对这些振荡进行计数，并使时钟的精确度可用于应用。这种时钟装置是基于一种能发射被称为频率梳的短脉冲的激光。这些梳子就像是时钟的闪光灯：梳子使我们能够非常精确地定位每一百万次振荡，使计数速度处于电子技术的范围内，而不是对每一次振荡进行计数。不幸的是，这些频率梳目前还不够坚固和成熟，不能在实验室受控环境之外长期运行。这项研究将使用数字信号处理技术和统计学来分析、设计和控制稳健的频率梳系统，这些系统可以像未来光学时钟所需的那样可靠和准确地运行。

This proposal aims to develop optical clockworks, the systems used to read out the time from an optical clock. An optical clock uses a very stable laser, referenced to an isolated atom's or multiple atoms' transition frequency to provide very fine and accurate subdivisions of time. Its precision comes from the very high frequency of oscillation of light compared to usual radio frequency oscillators, but this also makes it difficult to read the clock because the frequency is too high for conventional electronic means. Since these optical clocks already enable better time measurements and are likely to soon replace radio frequency atomic clock in time and frequency standards, it is very important that we develop the basic technology to support them. ***Measuring time accurately is a fundamental process, required for a wide range of applications, from answering deep scientific questions about our physical world (searching for gravitational waves, mapping gravity field distortions from the Earth and planets, testing for possible changes in what we now consider physical constants), to enabling very practical applications of accurate global navigation, high efficiency communications systems and many more. Often, the limit to the precision of these scientific and technological endeavours is linked to the performance of its clock. ***To build a clock, we need a stable, repeatable physical phenomenon (here, the oscillation of the laser electromagnetic field locked to an atomic transition) but also the means to count the number of these oscillations that have occurred. Every optical clock thus requires commensurate optical clockwork to count these oscillations and make the clocks' exquisite accuracy available for applications. Such clockwork is based on a type of laser emitting short pulses called frequency combs. These combs serve as a kind of strobe light for the clock: instead of counting each and every oscillation, combs enable us to very precisely pinpoint one every million oscillations, bringing the counting rate within the range of electronic techniques. Unfortunately these frequency combs are currently not robust and mature enough to operate for long term and outside the controlled environment of the laboratory. This research will use digital signal processing techniques and statistics to analyze, design and control robust frequency comb systems that can operate as reliably and accurately as optical clocks will require in the future.