Nuclear quadrupole interaction and zero first-order Zeeman transitions of 167Er3+ in CaWO4

Abstract

We report microwave spectroscopy of 167Er3+ doped in CaWO4, which reveals the hyperfine splitting of the erbium electronic ground state (Z1, Jeff = 15/2) induced by the I = 7/2 nuclear spin. From spectra measured below ∼50 mK in magnetic fields up to 200 mT, we extract spin-Hamiltonian parameters including the electron g, hyperfine A, and nuclear electric quadrupolar Q tensors. Crucially, our analysis demonstrates unambiguously that the previously unobserved nuclear electric quadrupolar moment is essential to reproduce the experimental data. With these refined parameters, we identify zero first-order Zeeman (ZEFOZ) transitions at zero magnetic field. Extending the analysis to finite fields, we uncover that ZEFOZ points lie either along the c axis or within the a-b plane. These results establish CaWO4 as a promising host for long lifetime quantum memories.