at milliKelvin temperatures*

Erbium (Er³⁺) ions in solid-state hosts are a promising platform for quantum networks and hybrid quantum systems ^[1] due to their long spin coherence times and telecom band optical transition at 1.54 μm. We perform continuous wave (cw) and pulsed Electron Spin Resonance (ESR) spectroscopy of erbium (¹⁶⁷Er³⁺) dopants in Y₂O₃ ^[2]. We report the estimated electron Zeeman g and hyperfine A tensor measured with X-band cw-ESR. We perform milliKelvin pulsed ESR at 5 GHz to measure Hahn-Echo electron spin coherence time of 1.5 millisecond and with a further enhancement to 8 milliseconds with dynamic decoupling. We further report the device development of superconducting low impedance resonator on epitaxially grown thin-film Y₂O₃ ^[3] to allow for further increased coupling rates between the cavity photons and electron spins on the order of kHz for high-sensitivity ESR.

[1] Lewis A. Williamson et al., Phys. Rev. Lett. 113, 203601 (2014)
[2] R. Fukumori et at, Phys. Rev. B 101, 214202 (2020)
[3] Manish Singh et al, APL Materials 8, 03111 (2020)