Now, world's most accurate clock ever

A team of physicists in Germany has built the most accurate timepiece on Earth, achieving unprecedented levels of accuracy with a new atomic clock.

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far.

As early as 1981, Hans Dehmelt, who was to be awarded a Nobel Prize later, had already developed the basic notions of how to use an ion kept in a high-frequency trap to build a clock which could attain the then unbelievably low relative measurement uncertainty in the range of 1E-18.

Ever since, an increasing number of research groups worldwide have been trying to achieve this with optical atomic clocks (either based on single trapped ions or on many neutral atoms). The PTB scientists are the first to have reached the finishing line using a single-ion clock.

Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18.

The definition and realization of the SI unit of time, the second, is currently based on cesium atomic clocks. Their "pendulum" consists of atoms which are excited into resonance by microwave radiation (1E10 Hz). It is regarded as certain that a future redefinition of the SI second will be based on an optical atomic clock. These have a considerably higher excitation frequency (1E14 to 1E15 Hz), which makes them much more stable and more accurate than cesium clocks.

The accuracy now achieved with the ytterbium clock is approximately a hundred times better than that of the best cesium clocks.

The results have been published in Physical Review Letters.