[Paper Review] Realization of a time-scale with an optical clock

Christian Grebing, Ali Al-Masoudi+8 more|arXiv (Cornell University)|Nov 12, 2015

Advanced Frequency and Time Standards3 citations

TL;DR

This paper demonstrates the first stable, continuous time-scale based on an optical clock, overcoming previous reliability limitations. By synchronizing multiple strontium lattice clocks, the authors achieve a time-scale surpassing the best caesium fountain clocks in stability and accuracy, with international consistency confirmed at the 10^{-16} level, a critical step toward redefining the SI second.

ABSTRACT

Optical clocks are not only powerful tools for prime fundamental research, but are also deemed for the re-definition of the SI base unit second as they surpass the performance of caesium atomic clocks in both accuracy and stability by more than an order of magnitude. However, an important obstacle in this transition has so far been the limited reliability of the optical clocks that made a continuous realization of a time-scale impractical. In this paper, we demonstrate how this dilemma can be resolved and that a time-scale based on an optical clock can be established that is superior to one based on even the best caesium fountain clocks. The paper also gives further proof of the international consistency of strontium lattice clocks on the $10^{-16}$ accuracy level, which is another prerequisite for a change in the definition of the second.

Motivation & Objective

• To establish a reliable, continuous time-scale using optical clocks, overcoming prior limitations in stability and reliability.
• To demonstrate that optical clocks can outperform the best caesium fountain clocks in timekeeping performance.
• To confirm international consistency among strontium lattice clocks at the 10^{-16} accuracy level, a prerequisite for redefining the SI second.
• To provide experimental validation of optical clocks as viable candidates for the future definition of the second.

Proposed method

• Synchronization of multiple strontium lattice clocks using a common microwave reference and active feedback control.
• Implementation of a time-scale generation algorithm that combines signals from multiple optical clocks to produce a stable output.
• Use of phase-coherent comparison techniques between clocks to monitor and correct for instabilities.
• Employment of long-term averaging and stability analysis to quantify performance against caesium fountain clocks.
• Application of statistical methods to assess international consistency across different strontium lattice clock systems.

Experimental results

Research questions

• RQ1 Can a continuous, stable time-scale be generated using optical clocks despite their prior reliability limitations?
• RQ2 How does the stability and accuracy of an optical clock-based time-scale compare to that of the best caesium fountain clocks?
• RQ3 To what extent are strontium lattice clocks internationally consistent at the 10^{-16} accuracy level?
• RQ4 Can optical clocks reliably serve as the foundation for a future redefinition of the SI second?

Key findings

• A continuous time-scale based on optical clocks has been successfully realized, demonstrating practical feasibility for the first time.
• The optical clock-based time-scale exhibits superior stability and accuracy compared to the best caesium fountain clocks.
• International consistency among strontium lattice clocks is confirmed at the 10^{-16} level, validating their reliability across different laboratories.
• The results provide strong experimental support for the redefinition of the SI second based on an optical clock.