Highly charged ion (HCI) clocks: Frontier candidates for testing variation of fine-structure constant

Attempts are made to unify gravity with the other three fundamental forces of nature. As suggested by higher dimensional models, this unification may require space and time variation some dimensionless constants. In scenario, probing temporal electromagnetic fine structure constant (α=e2ℏc) in a low energy regime at cosmological scale is immense interest. Atomic clocks ideal candidates for α because their transition frequencies measured ultra-high precision. Since atomic frequency function , measurement clock different spatial locations can yield signatures ascertain . Highly charged ions (HCIs) very sensitive least affected external perturbations, making them excellent platforms searching work, we overview HCIs suitable building spectroscopic features sensitivity The selection HCI outlined based on two general rules—by analyzing trends splitting level-crossing patterns along series isoelectronic systems periodic table. Two variants relativistic many-body methods configuration interaction coupled-cluster theory frameworks employed determine properties proposed clocks. These treat electronic correlation effects under frame Dirac-Coulomb Hamiltonian rigorously, while higher-order included approximately. Typical systematic measurements discussed using calculated properties. This review will help understand limits potentials as prospective guide future experiments.