Investigations of ${\mathrm{Ra}}^{+}$ properties to test possibilities for new optical-frequency standards

The present work tests the suitability of the narrow transitions $7s{}^{2}S_{1∕2}\to 6d{}^{2}D_{3∕2}$ and $7s{}^{2}S_{1∕2}\to 6d{}^{2}D_{5∕2}$ in ${\mathrm{Ra}}^{+}$ for optical frequency standard studies. Our calculations of the lifetimes of the metastable $6d$ states using the relativistic coupled-cluster theory suggest that they are sufficiently long for ${\mathrm{Ra}}^{+}$ to be considered as a potential candidate for an atomic clock. This is further corroborated by our studies of the hyperfine interactions, dipole and quadrupole polarizabilities, and quadrupole moments of the appropriate states of this system.

Figure 1

(Color online) Schematic diagram of energy levels of ${\mathrm{Ra}}^{+}$ with transitions for possible optical frequency standards.