Precision multi-mode microwave spectroscopy of paramagnetic and rare-earth ion spin defects in single crystal calcium tungstate

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Abstract

We present experimental observations of dilute ion spin ensemble defects in a low-loss single crystal cylindrical sample of CaWO4 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 × 10 7 , equivalent to a loss tangent of ∼ 3 × 10 − 8 . The low loss allowed precision multi-mode spectroscopy of numerous high Q-factor photon-spin interactions. Measurements between 7 and 22 GHz revealed the presence of Gd3+, Fe3+, 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.

Original languageEnglish
Article number164001
Number of pages7
JournalApplied Physics Letters
Volume125
Issue number16
DOIs
Publication statusPublished - 14 Oct 2024

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