Cryogenic microwave loss in epitaxial Al/GaAs/Al trilayers for superconducting circuits

TL;DR

This study measures microwave loss in epitaxial Al/GaAs/Al trilayers at millikelvin temperatures, revealing intrinsic and power-independent losses, with implications for superconducting quantum device performance.

Contribution

It provides the first detailed loss characterization of epitaxial Al/GaAs/Al trilayers, highlighting the impact of GaAs piezoelectricity on microwave loss.

Findings

Power-independent loss is approximately 4.8e-5.

TLS loss is approximately 6.4e-5.

Intrinsic TLS loss lower bound is 7.2e-5.

Abstract

Epitaxially-grown superconductor/dielectric/superconductor trilayers have the potential to form high-performance superconducting quantum devices and may even allow scalable superconducting quantum computing with low-surface-area qubits such as the merged-element transmon. In this work, we measure the power-independent loss and two-level-state (TLS) loss of epitaxial, wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped element superconducting microwave resonators at millikelvin temperatures and down to single photon powers. The power-independent loss of the device is $(4.8 \pm 0.1) \times 10^{-5}$ and resonator-induced intrinsic TLS loss is $(6.4 \pm 0.2) \times 10^{-5}$. Dielectric loss extraction is used to determine a lower bound of the intrinsic TLS loss of the trilayer of $7.2 \times 10^{-5}$. The unusually high power-independent loss is attributed to GaAs's intrinsic piezoelectricity.