Losses in Josephson junction resonators

Josephson junctions for superconducting circuits such as SQUIDs and qubits are conventionally based on Al-AlO$_x$-Al multilayer technology, which was shown to have a low quality factor and two-level-fluctuators in the dielectric AlO$_x$ as limiting decoherence source. By replacing the amorphous Al-rich tunnel oxide with nearly stoichiometric Al$_2$O$_3$ we aim to increase the qubit coherence times by reducing the number of dangling bonds in the Josephson tunnel junction. In this talk a test platform for loss determination in high-Q tunnel oxides based on junction resonators will be presented. We will show alternative tunnel junctions based on high temperature grown tunnel oxides.