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arXiv · 2605.18208

Phonon-bottlenecked spin relaxation of Er$^{3+}$:CaWO$_4$ at milliKelvin temperatures

S. Rajendran·B. Mistri·P. K. Sharma·S. E. Kubatkin·A. V. Danilov·S. Dhomkar·S. E. de Graaf·V. Ranjan
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Abstract

We study spin-lattice relaxation times of electron spins in Er$^{3+}$:CaWO$_4$ at millikelvin temperature, detected via their coupling to a low-mode volume superconducting resonator. At large magnetic field supporting strong phonon-emission rates, we observe a noticeable increase in relaxation times with increasing spin-excitations, which exhibit a unique $[\tanh (\hbar \omega_0/k_\text{B} T)]^2$ temperature dependence. These observations are typical of a phonon-bottlenecked spin relaxation, and have implications for quantum technologies that exploit rare-earth spin ensembles as coherent resources.

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S. Rajendran, B. Mistri, P. K. Sharma, S. E. Kubatkin, A. V. Danilov, S. Dhomkar, S. E. de Graaf, V. Ranjan. 2026-05-18. Phonon-bottlenecked spin relaxation of Er$^{3+}$:CaWO$_4$ at milliKelvin temperatures. https://arxiv.org/abs/2605.18208

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