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 Qi. To validate the simulation, we fabricate quarter wavelength coplanar waveguide resonators on GaAs and measure Qi as function of frequency, power and temperature. We observe a linear increase of Qi with frequency, as predicted by the simulations for a constant electromechanical coupling. Additionally, Qi 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.
Highlights
Superconducting coplanar waveguide (CPW) resonators in the microwave regime have been extensively used in circuit quantum electrodynamics because of their high performance (e.g. internal quality factors (Qi) can exceed 1 million [1])
We investigate the mechanical loss channel of superconducting CPW resonators fabricated on gallium arsenide (GaAs)
The internal quality factor of CPW resonators on GaAs is mainly limited by the conversion of the photons stored in the resonator to mechanical waves that dissipate energy into the substrate
Summary
Superconducting coplanar waveguide (CPW) resonators in the microwave regime have been extensively used in circuit quantum electrodynamics (circuitQED) because of their high performance (e.g. internal quality factors (Qi) can exceed 1 million [1]). Well established and consistent fabrication techniques lead to devices that match its designed parameters, allowing for the implementation of circuits with many multiplexed resonators [2] Such resonators have a high spatial confinement of the electric field that enhances the zero point fluctuations, making the resonators suitable for srtong coupling with other quantum systems [3, 4]. One finds the same aforementioned factors responsible for the energy loss of other devices in circuit QED, such as quantum bits (qubits) [12]. This is not surprising since the resonators are fabricated with the same materials, following the same lithographic process, are measured in the same environment and with the same electromagnetic excitation
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