This paper outlines the roadmap towards the redefinition of the second, which was recently
updated by the CCTF Task Force created by the CCTF in 2020. The main achievements of …

Transportable strontium optical lattice clocks are developed with a fractional uncertainty of
5.5× 10− 18 for applications outside laboratories. A single clock consists of a spectroscopy …

We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space
concerning the status of cold atom technologies, the prospective scientific and societal …

We present a liquid-nitrogen-cooled Ca+ optical clock with an overall systematic uncertainty
of 3.0× 10− 18. In contrast to the room-temperature Ca+ optical clock that we have reported …

We present a transportable ultra-stable clock laser system based on a Fabry–Perot cavity
with crystalline Al_0. 92Ga_0. 08As/GaAs mirror coatings, fused silica (FS) mirror substrates …

We present the compact long-term nearly continuous operation of a room-temperature Ca+-
optical-clock setup towards a transportable clock, achieving an overall systematic …

We report a robust, compact, and transportable optical clock (TOC-729-2) based on a
trapped single 40 Ca+ ion with a systematic uncertainty of 1.1× 10− 17⁠, which is limited by …

In this review, the improvements made in the past two decades for 40 Ca+ optical clocks in
China are presented. Uncertainty of below 1.3× 10− 17 was achieved by applying the …

Optical clocks are emerging as next-generation timekeeping devices with technological and
scientific use cases. Simplified atomic sources such as vapor cells may offer a …

Geopotential and orthometric height differences between distant points can be measured via
timescale comparisons between atomic clocks. Modern optical atomic clocks achieve …