Characterizing Loss Channels in Tantalum Transmons using Lumped Element Resonators

Superconducting qubits based on tantalum have achieved record lifetimes and coherence times for planar transmons. The microscopic mechanisms for loss in these devices are poorly understood. In this talk, we present some progress in characterizing loss channels using lumped element (LE) resonators. Consisting of a capacitor and a meander inductor, LE resonators can be made to be geometrically representative of various kinds of transmon qubits, and can therefore be used to probe the loss channels that currently limit their coherence. By varying surface treatment, device geometry, device packaging, temperature, and power, we can separately characterize the effects of two-level systems (TLS's), bulk losses, and packaging on resonator coherence. We find that when the participation of surface oxides is minimized, the coherence of the LE resonators is limited by a temperature- and power-independent loss channel.