Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants

Mikhael T. Sayat; Federico Pisani; Hin Lok Chang; Yaroslav Zhumagulov; Kirrily C. Rule; Tom Fennell; Jakob Nunnendorf; Chee Kwan Gan; Oleg V. Yazyev; Ping Koy Lam; Jian-Rui Soh

arXiv · 2602.08525

Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants

Mikhael T. Sayat·Federico Pisani·Hin Lok Chang·Yaroslav Zhumagulov·Kirrily C. Rule·Tom Fennell·Jakob Nunnendorf·Chee Kwan Gan·Oleg V. Yazyev·Ping Koy Lam·Jian-Rui Soh

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Abstract

We investigate the lattice dynamics of CaWO$_4$, 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 Er$^{3+}$ crystal-field operators, including a low-energy $B_g$ 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 CaWO$_4$ and establish a basis for engineering phononic environments to mitigate the loss of stored quantum states and optimize Er-doped CaWO$_4$ for quantum-memory applications.

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Mikhael T. Sayat, Federico Pisani, Hin Lok Chang, Yaroslav Zhumagulov, Kirrily C. Rule, Tom Fennell, Jakob Nunnendorf, Chee Kwan Gan, Oleg V. Yazyev, Ping Koy Lam, Jian-Rui Soh. 2026-02-09. Coupling between CaWO$_4$ phonons and Er$^{3+}$ dopants. https://arxiv.org/abs/2602.08525

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