Characterizing the coherence of tantalum-based transmons and resonators*

Scaling quantum machines requires ever-increasing numbers of qubits with ever-higher coherence. In superconducting circuits, there have been recent advances combining careful surface preparation and metals such as tantalum for non-Josephson junction circuit elements which have achieved record coherences.

In this talk, we will summarize our work on improving coherence of tantalum-based superconducting transmons with aluminum Josephson junctions. We will discuss experimental data and calculations seeking to determine whether the dominant loss in our transmons and resonators is due to the tantalum-aluminum interface.  We also will show results on the effects of adopting dry-etching instead of wet-etching as the metal patterning fabrication method on the coherence of the transmons. We will present our qubits’ and resonators’ coherence data along with supporting fabrication characterization analysis using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDX) to gain a better understanding of our samples’ surfaces.

[Place, et al., Nat. Comm (2021)].