Theoretical characterisation of the barium II and radium II ions

Abstract

Motivated by recent experimental advances, including the ongoing development of an optical atomic clock in singly ionised radium, we perform a detailed theoretical characterisation of Ra+ and its lighter analogue, Ba+. Both ions are of interest for precision studies, including for atomic parity violation and searches for new physics beyond the standard model. Using the all-orders correlation potential method, including Breit and radiative quantum electrodynamics corrections, we perform high-accuracy calculations of electric-dipole (E1), electric-quadrupole (E2), and magnetic-dipole (M1) transition matrix elements between the low-lying s, p, and d states of these ions, as well as the excited-state lifetimes, polarizabilities, magic wavelengths, and magnetic dipole (A) hyperfine structure constants. By combining lifetime measurements with precise theoretical ratios, we extract high-accuracy determinations of the s-d_1/2 and s-d_3/2 E2 matrix elements. By combining hyperfine measurements with atomic theory, we extract parameters of the nuclear magnetisation distribution (the Bohr-Weisskopf effect) for 135-, 137-Ba and 223-, 225-Ra. These results provide theoretical input for ongoing and future experimental programs in fundamental physics and precision metrology.