M.A. Hosain^a, J.-M. Le Floch^a,b, J. Krupka^c, M.E. Tobar^a
a ARC Centre of Excellence for Engineered Quantum Systems, School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
b MOE Key Laboratory of Fundamental Physical Quantities Measurement, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China
c Department of Electronics and Information Technology, Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Koszykowa 75, 00-662 Warszawa, Poland

A cylindrical single crystal SrLaAlO4 Whispering Gallery mode dielectric resonator was cooled to millikelvin temperature using a dilution refrigerator. By controlling a DC-magnetic field, impurity ions’ spins were coupled to a variety of modes allowing the measurement of hybrid spin-photon systems. This Electron Spin Resonance mapping technique allowed us to detect Cu²⁺, Fe³⁺ and Mn⁴⁺ impurity ions (at the level of parts per million (ppm) to parts per billion (ppb)), verified by the measurement of the spin parameters along with their site symmetry. Whispering Gallery modes exhibited Q-factors >10⁵ at a temperature less than 20 mK, allowing sensitive spectroscopy with high precision. Measured hyperfine line constants of the Cu2+ ion shows different parallel g-factors, g_||Cu, of 2:526; 2:375; 2:246 and 2:142. The spin-orbit coupling constant of the Cu²⁺ ion was determined to be Lambda~ 635 cm^{- 1}. The low-spin state Fe3+ ion’s measured parallel g-factor, g_||Fe, of 2:028 reveals tetragonal anisotropy. The Mn⁴⁺ ion is identified in the lattice, producing hyperfine structure with high-valued g-factors,g_||Mn, of 7:789; 7:745; 7:688; 7:613; 7:5304 and 7:446. The hyperfine structures of the Cu²⁺ and Mn⁴⁺ ions show broadening of about 79 G between 9:072 GHz and 10:631 GHz, and 24:5 G broadening between 9:072 GHz and 14:871 GHz, respectively.

http://dx.doi.org/10.1016/j.jmr.2017.06.007