Distinguishing and Mitigating Decoherence Mechanisms in Transmon Qubits*

Extending the coherence times of superconducting qubits relies on iterative improvement of materials, fabrication processing, and design in order to distinguish and subsequently mitigate the numerous sources of decoherence. In this talk, we will outline the characterization tools that we use to assess many of the dominant contributions to energy relaxation in superconducting qubits, including dielectric two-level systems and nonequilibrium quasiparticles, as a step towards developing a holistic account of transmon decoherence.