Erbium and thulium on MgO(100)/Ag(100) as candidates for single atom qubits

Lanthanide atoms on surfaces are an exceptional platform for atomic-scale magnetic information storage. However, their potential as qubits remains unexplored due to the limited number of experimental setups that can coherently drive the spins of single adatoms. Here we propose a combined experimental and theoretical method to estimate the performance of surface-adsorbed lanthanide atoms for quantum coherent operations. We investigate Er and Tm on MgO(100)/Ag(100) with x-ray absorption spectroscopy to address their magnetic and electronic properties and with scanning tunneling microscopy (STM) to identify their adsorption sites. With atomic multiplet calculations and density functional theory, we infer for both atoms a magnetic ground state that is suitable for quantum coherent operations. We investigate whether these systems lend themselves to electron spin resonance scanning tunneling microscopy (ESR-STM). By adapting the piezoelectric model of ESR-STM to the case of lanthanide atoms, we show that these systems should exhibit a detectable signal and that they have a higher Rabi rate compared to the systems studied up to date. In addition to their suitable electron spin properties, these elements possess a nontrivial nuclear spin that could be exploited to perform two-qubit operations on a single atom or to store quantum states in the nuclear spin.