We investigate the lattice dynamics of CaWO4, a promising host crystal for erbium-based quantum memories, using inelastic neutron scattering together with density-functional perturbation theory. The measured phonon dispersion along the (100), (001), and (101) reciprocal space direction reveals phonon bands extending up to 130 meV, with a gap between 60 and 80 meV, in good agreement with our calculations. From a symmetry analysis of the phonon eigenmodes, we identify eight Raman-active modes that can couple directly to the Er3+ crystal-field operators, including a low-energy Bg mode at 9.1 meV that is expected to play a dominant role in phonon-assisted spin-lattice relaxation. These results provide a microscopic description of the phonon bath in CaWO4 and establish a basis for engineering phononic environments to mitigate the loss of stored quantum states and optimize Er-doped CaWO4 for quantum-memory applications.
@article{arxiv.2602.08525,
title = {Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants},
author = {Mikhael T. Sayat and Federico Pisani and Hin Lok Chang and Yaroslav Zhumagulov and Kirrily C. Rule and Tom Fennell and Jakob Nunnendorf and Chee Kwan Gan and Oleg V. Yazyev and Ping Koy Lam and Jian-Rui Soh},
journal= {arXiv preprint arXiv:2602.08525},
year = {2026}
}