Advances in optical spectroscopy of trapped atoms and ions have achieved unprecedented measurement precision, with relative uncertainty reaching parts per billion billion. Such precision opens new perspectives for exploring physics beyond the Standard Model, complementing research conducted through high-energy particle collisions and astronomical and cosmological studies.
The frequency shifts of atomic spectral lines between different isotopes reveal subtle changes in the properties of nuclei. Optical spectroscopy has long been used to extract variations in the nuclear charge radius between isotopes. However, with the advent of ultra-high-precision spectroscopy, it is now possible to access finer aspects of nuclear structure.
Isotope shift is also proving to be a unique probe for exploring physics beyond the Standard Model, particularly for testing the existence of a fifth force. It is particularly sensitive to minute connections between neutrons and electrons, effects so faint that they go undetected in classical particle physics experiments.
This article presents the progress made in this field, the challenges encountered, and the promising prospects for the future.