Cryogenic Microwave Loss In Epitaxial Al/Gaas/Al Trilayers For Superconducting Circuits

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 +/- 0.1 ) x10- 5, and the resonator-induced intrinsic TLS loss is( 6.4 +/- 0.2 ) x10- 5. Dielectric loss extraction is used to determine a lower bound of the intrinsic TLS loss of the trilayer of7.2 x10- 5. The unusually high power-independent loss is attributed to GaAs's intrinsic piezoelectricity.