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A calcium tungstate (CaWO₄) crystal is like a musical instrument: its atoms vibrate like strings, and these vibrations can 'drown out' fragile quantum information. To understand exactly how this happens, scientists bombarded the crystal with neutrons and recorded the response — producing a map of all possible vibrations, from low notes to very high ones.

It turned out that in this 'music' there is a quiet region: between 60 and 80 meV (a unit of vibration energy) there are almost no vibrations, but above that they resume, up to 130 meV. Among all the vibrations, one stood out — at an energy of 9.1 meV. It acts like a hand that plucks a string when an erbium ion (a rare-earth metal that stores the quantum state) enters the crystal. It is through this vibration that quantum information most quickly 'leaks' into heat.

Now that the exact 'score' of vibrations is known, engineers can tweak the crystal's composition or temperature to dampen the problematic vibration. Such a crystal doped with erbium is a candidate for memory in future quantum computers, where data is stored in the states of individual ions.

This research doesn't just describe a material: it offers a recipe: how to tune the crystal lattice so that quantum information lasts longer. It's a step from a beautiful idea to a working device.

Original abstract

as written by the authors arXiv:2602.08525

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.