Fluctuations of Qubit Energy-Relaxation Times

Superconducting qubits are a leading candidate for utility-scale quantum computing. For continued progress, it is necessary to understand and mitigate decoherence, which is dominated by defects that reside at amorphous interfaces. Here, we characterize the energy relaxation of flux-tunable transmons over a range of bias points to access the spectral fingerprint of the local defect bath. In addition, we monitor fluctuations of qubit energy relaxation as a function of time. We study the dependence of qubit loss and defect distribution on geometry, varying both the separation between qubit shunt capacitor electrodes and the shape of the qubit junction leads.