Superconducting cavity-electromechanics on silicon-on-insulator

TL;DR

This paper reports the development of superconducting microwave resonators on silicon membranes and their coupling to mechanical resonators, demonstrating high-Q factors, strong electromechanical coupling, and microwave back-action cooling at millikelvin temperatures.

Contribution

It introduces a novel fabrication process for high-Q superconducting resonators on silicon-on-insulator wafers and characterizes their coupling to mechanical resonators at cryogenic temperatures.

Findings

Achieved a vacuum coupling rate of approximately 24.6 Hz.

Measured a mechanical Q-factor of 1.7×10^7.

Realized microwave back-action cooling to about 16 phonons.

Abstract

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 $8.9$GHz coil resonator is coupled capacitively with large participation ratio to a $9.7$MHz 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 $T_f = 11$~mK, yielding a measured electromechanical vacuum coupling rate of $g_{0}/2\pi \approx 24.6$~Hz and a mechanical resonator $Q$-factor of $Q_{m}=1.7\times 10^7$. Microwave back-action cooling of the mechanical resonator is also studied, with a minimum phonon occupancy of $n_{m} \approx 16$ phonons being realized at an elevated fridge temperature of $T_f = 211$~mK.