Phononic loss in superconducting resonators on piezoelectric substrates

TL;DR

This study combines numerical simulations and experimental measurements to analyze phononic losses in superconducting resonators on piezoelectric substrates, identifying fundamental loss mechanisms and their impact on resonator quality factors.

Contribution

It provides the first combined numerical and experimental analysis of phononic loss mechanisms in superconducting resonators on piezoelectric materials, highlighting electromechanical coupling effects.

Findings

Q_i increases linearly with frequency

Weak power dependence of Q_i

Negligible temperature dependence at 10 mK

Abstract

We numerically and experimentally investigate the phononic loss for superconducting resonators fabricated on a piezoelectric substrate. With the help of finite element method simulations, we calculate the energy loss due to electromechanical conversion into bulk and surface acoustic waves. This sets an upper limit for the resonator internal quality factor $Q_i$. To validate the simulation, we fabricate quarter wavelength coplanar waveguide resonators on GaAs and measure $Q_i$ as function of frequency, power and temperature. We observe a linear increase of $Q_i$ with frequency, as predicted by the simulations for a constant electromechanical coupling. Additionally, $Q_i$ shows a weak power dependence and a negligible temperature dependence around 10$\,$mK, excluding two level systems and non-equilibrium quasiparticles as the main source of losses at that temperature.