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arXiv · 2312.05199

Precision Multi-Mode Microwave Spectroscopy of Paramagnetic and Rare-Earth Ion Spin Defects in Single Crystal Calcium Tungstate

Elrina Hartman·Michael E Tobar·Ben T McAllister·Jeremy Bourhill·Maxim Goryachev
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Abstract

We present experimental observations of dilute ion spin ensemble defects in a low-loss single crystal cylindrical sample of CaWO$_4$ cooled to $30$ mK in temperature. Crystal field perturbations were elucidated by constructing a dielectrically loaded microwave cavity resonator from the crystal. The resonator exhibited numerous whispering gallery modes with high $Q$-factors of up to $3\times 10^7$, equivalent to a loss tangent of $\sim 3\times 10^{-8}$. The low loss allowed precision multi-mode spectroscopy of numerous high $Q$-factor photon-spin interactions. Measurements between 7 to 22 GHz revealed the presence of Gd$^{3+}$, Fe$^{3+}$, and another trace species, inferred to be rare-earth, at concentrations on the order of parts per billion. These findings motivate further exploration of prospective uses of this low-loss dielectric material for applications regarding precision and quantum metrology, as well as tests for beyond standard model physics.

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Elrina Hartman, Michael E Tobar, Ben T McAllister, Jeremy Bourhill, Maxim Goryachev. 2023-12-08. Precision Multi-Mode Microwave Spectroscopy of Paramagnetic and Rare-Earth Ion Spin Defects in Single Crystal Calcium Tungstate. https://doi.org/10.1063/5.0224102

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