  Substrate material imperfections and surface losses are one of the major
factors limiting superconducting quantum circuitry from reaching the scale and
complexity required to build a practicable quantum computer. One potential path
towards higher coherence of superconducting quantum devices is to explore new
substrate materials with a reduced density of imperfections due to inherently
different surface chemistries. Here, we examine two ternary metal oxide
materials, spinel (MgAl2O4) and lanthanum aluminate (LaAlO3), with a focus on
surface and interface characterization and preparation. Devices fabricated on
LaAlO3 have quality factors three times higher than earlier devices, which we
attribute to a reduction in interfacial disorder. MgAl2O4 is a new material in
the realm of superconducting quantum devices and, even in the presence of
significant surface disorder, consistently outperforms LaAlO3. Our results
highlight the importance of materials exploration, substrate preparation, and
characterization to identify materials suitable for high-performance
superconducting quantum circuitry.
