Superconducting cavity-electromechanics on silicon-on-insulator

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Fabrication processes involving anhydrous hydrofluoric vapor etching are developed to create high-Q aluminum superconducting microwave resonators on free-standing silicon membranes formed from a silicon-on-insulator wafer. Using this fabrication process, a high-impedance 8.9GHz coil resonator is coupled capacitively with large participation ratio to a 9.7MHz micromechanical resonator. Two-tone microwave spectroscopy and radiation pressure back-action are used to characterize the coupled system in a dilution refrigerator down to temperatures of Tf = 11 mK, yielding a measured electromechanical vacuum coupling rate of g₀/2π≈ 24.6 Hz and a mechanical resonator Q-factor of Qₘ=1.7× 10⁷. Microwave back-action cooling of the mechanical resonator is also studied, with a minimum phonon occupancy of nₘ ≈ 16 phonons being realized at an elevated fridge temperature of Tf = 211 mK.