Cesium133Hyperfeinfrequenz

Cesium-133 hyperfine transition refers to the energy difference between the two hyperfine levels of the ground state of the cesium-133 atom. This transition underpins the definition of the SI second and serves as the basis for many of the world’s most precise timekeeping devices. The ground state of cesium-133 is split into two levels, commonly labeled F = 3 and F = 4, whose energy separation corresponds to a microwave frequency used for timekeeping.

The hyperfine splitting arises from the interaction between the nuclear magnetic moment and the magnetic field produced by the electrons. The transition between the two hyperfine levels is highly stable and reproducible, allowing it to act as an excellent frequency standard. The transition frequency is defined to be exactly 9,192,631,770 hertz, a value fixed for the purpose of defining the second. In practice, frequency measurements are realized by observing induced transitions with microwaves and counting cycles over long interrogation times to achieve high accuracy.

Atomic clocks that use the cesium-133 hyperfine transition come in several designs, including fountain clocks, beam clocks, and room-temperature or laser-cooled configurations. Modern realizations often employ Ramsey interrogation methods and advanced stabilization techniques to minimize environmental perturbations such as magnetic fields, temperature, and motion of the atoms.

Applications of cesium-133-based time standards include global navigation satellite systems, telecommunications synchronization, and fundamental metrology. While optical clocks are advancing and challenging the supremacy of cesium for primary standards, the cesium-133 hyperfine transition remains a central reference for time and frequency metrology and for calibrating other clock technologies.