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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

quant-phSubmitted May 18, 2026• Announced May 19, 2026• 0 citations
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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 $[\tanh (\hbar ω_0/k_\text{B} T)]^2$ 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.

Comments
9 pages, 10 figures including supplementary information

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