Electrical control of the nuclear spin states of rare-earth adatoms

Rare-earth adatoms on the surfaces have been studied for potential quantum sensing and quantum computing applications. Despite extensive experimental efforts, a full description of the electronic configurations of the adatoms remains elusive. Here we investigate two charge states and several electronic configurations for a Sm adatom on a MgO substrate using multiconfigurational ab-initio methods, for the possibility of using the Sm nuclear spin levels as qubits. For the configurations in a neutral charge state, the electronic ground state is effectively a singlet, and so the hyperfine interaction associated with the ¹⁴⁷Sm nucleus is absent, which may greatly enhance nuclear spin coherence time. We show that the splitting of the nuclear levels can be controlled by a static electric field, and that Rabi oscillations can be induced by a time-dependent electric field. For the configurations in a singly charged state, electronic Kramers doublets are formed. The electronic configurations including an unpaired 6s orbital exhibit a strong hyperfine Stark effect and Rabi oscillations between the electronic-nuclear levels whose frequencies are up to three orders of magnitude higher than those for the neutral charge state. Our findings may be experimentally realized within scanning tunneling microscopy.