Precision measurement of electronic ion-ion interactions between neighboring Eu3⁺ optical centers

We report measurements of discrete excitation-induced frequency shifts on the F07→D05 transition of the Eu3⁺ center in La:Lu:EuCl ₃·6D₂O resulting from the optical excitation of neighboring Eu3⁺ ions. Shifts of up to 46.081±0.005 MHz were observed. The magnitude of the interaction between neighboring ions was found to be significantly larger than expected from the electric dipole-dipole mechanism often observed in rare earth systems. We show that a large network of interacting and individually addressable centers can be created by lightly doping crystals otherwise stoichiometric in the optically active rare earth ion, and that this network could be used to implement a quantum processor with more than ten qubits.