Preface

Abstract

The 9th Symposium on Frequency Standards and Metrology [1] was held from the 16th to 20th of October at the Mantra on Salt Beach Resort in Kingscliff, New South Wales, Australia. The Symposium included a keynote lecture plus another 47 invited oral presentations and 105 invited poster contributions continually displayed over the week with two dedicated poster sessions. The Symposium is the most recent one of a series [2] that was initially organized by Jacques Vanier in 1971 in Forêt Montmorency in Quebec, Canada. The next ones took place in 1976 in Copper Mountain, USA, organized by Helmut Hellwig, 1981 in Aussois, France (Claude Audoin) [3], 1988 in Ancona, Italy (Andrea De Marchi) [4], 1995 in Woods Hole, USA (James Bergquist) [5], 2001 in St Andrews, UK (Patrick Gill) [6], 2008 in Pacific Grove, USA (Lute Maleki) [7], and in 2015 Potsdam, Germany (Fritz Riehle) [8]. The symposium series serves as an international discussion forum on precision frequency standards throughout the electromagnetic spectrum and associated metrology. It focuses on the fundamental scientific aspects of the latest ideas, results and applications in relation to these frequency standards. During the seven years after the last symposium very significant progress has occurred in various associated fields. The 9th Symposium, focusing on frequency standards and related metrology, was held at an historically significant time, as metrology recently underwent a radical change in the definitions of the SI base units. In 2019, these units were redefined in terms of physical constants, with time playing a central role, as the definition of the second, based on the ground state hyperfine frequency of the caesium atom, now influences the definition of all base units (except the mole). The symposium series remains a crucial meeting, with many laboratories conducting studies on optical frequency standards, a promising area with the potential to replace microwave frequency standards for a possible redefinition of the second. This could significantly impact the SI unit system. The realisation of the second based on caesium standards appears to have reached its accuracy limit at the level of 10−16. In contrast, the use of optical radiations allows for the realisation of frequency standards with accuracy at the level of 10−18 and beyond. Related to this, in 2016, the Consultative Committee for Time and Frequency (CCTF) published the first roadmap towards redefining the second. By 2020, the CCTF established a task force comprising about 40 experts from around the world to update this roadmap in preparation for a potential redefinition of the second in the coming years. The fundamentals of this process, along with the criteria that must be met and the challenges involved, are detailed in an open-source paper that fully supports the presentation by Tavella given at the 9th Symposium on Frequency Standards and Metrology [9]. List of Committees, Symposium Photographs, Sponsors and Participants of the 9FSM, 2024, Peer review statement are available in this pdf.