Optical atomic clocks are considered to be the atomic clocks of the future. They are already "ticking", but the unit second is still defined by caesium atomic clocks. In these, caesium atoms are excited by microwave radiation, whereas the atoms or ions in optical clocks are excited by optical radiation. The more frequent oscillations per unit of time of light compared to microwaves allow the frequency of these atomic clocks to be determined with far greater accuracy. Researchers at the Physikalisch-Technische Bundesanstalt (PTB) have now succeeded in precisely determining a decisive influencing factor on this reference frequency, the temperature of the environment. The new method is based on the fact that even the smallest frequency shifts are directly correlated with temperature. To this end, the researchers compared two optical atomic clocks with each other and were able to determine the frequency of the reference transition of strontium ions with three times greater accuracy. This measurement paves the way for a future redefinition of the second. The results of the study are published in the current issue of the journal Physical Review Letters.
