Metal-air surface dielectric loss characterization of rhenium superconducting circuits

There is a continued effort to improve the coherence times of superconducting circuits as a platform for quantum computing. Recent works have targeted the metal-air surface as a significant source of loss, giving rise to approaches utilizing improved surface treatments and surface encapsulation. However, in a planar architecture, metal-air surface dielectric loss is not separable from other surface losses using standard devices such as multimode resonators. By employing a flip-chip architecture, we magnify sensitivity to metal-air loss by orders of magnitude, enabling an unambiguous extraction of a metal-air loss factor. To demonstrate our technique, we characterize rhenium as a novel materials platform for superconducting circuits, motivated by the thinner native oxide film compared to other state-of-the-art materials such as tantalum. We present preliminary results from our loss characterization, in addition to coherence times that rival tantalum devices.