There are atoms that can count a second with a very big precision if they are "asked" to do it. The best known today are cesium and strontium, to my knowledge. But the question is to know if in each of these atoms is there a single perfect transition to do this work or is it possible that there are several in a same atom?
Hello! Yes when it comes to atomic timekeeping and the definition of the second, cesium and strontium atoms play very importan roles. Well cesium has been the gold standard for timekeeping for many years. The reason cesium is so valuable in this context is because of a very specific transition within its atomic structure. The international definition of a second is based on the precise measurement of the periods of radiation corresponding to the transition between two hyperfine levels of the ground state in a cesium-133 atom. This is a singular, unique transition that has been chosen because of its consistent and reliable frequency ... now, looking at strontium, there's a growing interest due to its potential for even more precise timekeeping. Strontium atoms are used in optical clocks, which operate at a higher frequency compared to the microwave frequencies used by cesium clocks. This higher frequency allows for a finer subdivision of the second and thus potentially more precise measurements. However, whether strontium uses one transition or multiple transitions for defining a second with such high accuracy is not as clearly established as with cesium.
