• Tobar, Michael
• Creedon, Daniel
• Johnson, Brett C.
• Jamieson, David
• Bourhill, Jeremy

Abstract

<p>Single crystal isotopically pure 28Si cylindrical Whispering Gallery (WG) mode resonators have been machined from a rod of isotopically pure crystal. Before machining, the rod was loaded into a cavity with the best Bragg confined modes exhibiting Q-factors above a million for frequencies between 10 and 15 GHz. Electron Spin Resonance spectroscopy revealed a very narrow linewidth spin transition, with g-factor of 1.995±0.008. Analysis determined an upper limit to the linewidth of 7 kHz and a concentration of less than 10¹¹ spins/cm³ (10 parts per trillion). After machining into WG mode resonators, the measured frequencies of the fundamental mode families were used to determine the relative permittivity of the material near 4 K and 20 mK to be 11.488±0.024, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded to below 40,000. Raman spectroscopy revealed strain induced broadening on the radial surface of the crystal as a result of the machining. After an acid clean and etch, followed by annealing, the surface damage was repaired. Subsequently, high Q-factors were also restored. The next step will be to purposefully implant ions to try and realise narrow linewidth spin ensembles with clock transitions, which will couple to high-Q WG modes inside the crystal.</p>

Topics

• surface
• single crystal
• dielectric constant
• laser emission spectroscopy
• electron spin resonance spectroscopy
• annealing
• Raman spectroscopy