Quantum Electromechanics on Silicon Nitride Nanomembranes

TL;DR

This paper introduces a silicon nitride nanomembrane platform integrating superconducting microwave circuits with optical and acoustic devices, achieving high impedance resonators and demonstrating strong electromechanical coupling and ground-state cooling.

Contribution

The work presents a novel silicon nitride nanomembrane platform enabling efficient microwave-to-mechanical coupling with high impedance resonators and demonstrated ground-state cooling.

Findings

Achieved vacuum gap sizes down to 80 nm in capacitors.

Measured electromechanical coupling rate of 41.5 Hz.

Reached mechanical mode occupancy as low as 0.58.

Abstract

We present a platform based upon silicon nitride nanomembranes for integrating superconducting microwave circuits with planar acoustic and optical devices such as phononic and photonic crystals. Utilizing tensile stress and lithographic patterning of a silicon nitride nanomembrane we are able to reliably realize planar capacitors with vacuum gap sizes down to $s \approx 80$nm. In combination with spiral inductor coils of micron pitch, this yields microwave ($\approx 8$GHz) resonant circuits of high impedance ($Z_{0} \approx 3.4$k$\Omega$) suitable for efficient electromechanical coupling to nanoscale acoustic structures. We measure an electromechanical vacuum coupling rate of $g_{0}/2\pi = 41.5$~Hz to the low frequency ($4.48$MHz) global beam motion of a patterned phononic crystal nanobeam, and through parametric microwave driving reach a backaction cooled mechanical mode occupancy as low as $n_{m} = 0.58$.