Atomikellad

Atomikellad, or atomic clocks, are timekeeping devices that determine time by measuring the frequency of electromagnetic radiation associated with transitions between energy levels in atoms. The most widely used reference relies on the cesium-133 atom, with rubidium and other atomic species used in various commercial and laboratory applications. The key advantage is the exceptional stability and reproducibility of atomic transition frequencies, which provide a highly precise and reproducible measure of time.

The SI second is defined as 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133. Atomic clocks realize this definition in laboratories and national metrology institutes, forming the basis for accurate timekeeping worldwide. In recent years, optical clocks based on higher-frequency transitions in atoms such as strontium or ytterbium have demonstrated greater short-term stability and potential long-term accuracy, but cesium-based clocks remain the official standard for defining the second.

Various architectures exist. Cesium fountain and cesium beam clocks use microwave radiation to probe atomic transitions, while rubidium clocks provide compact, lower-cost alternatives for many applications. Hydrogen masers offer superb short-term stability for certain timekeeping needs. Optical clocks, though not yet the basis of the SI second, represent the forefront of precision, offering improvements that may influence future redefinitions.

Applications of atomic clocks include global navigation satellite systems (such as GPS), telecommunications networks, power grids, and scientific research. They enable precise time transfer and synchronization across vast distances, supporting coordinated universal time (UTC) and critical infrastructure worldwide.