Dynamics of superconducting qubit relaxation times

Superconducting qubits are a leading candidate for quantum computing but display temporal fluctuations in their energy relaxation times T-1. This introduces instabilities in multi-qubit device performance. Furthermore, autocorrelation in these time fluctuations introduces challenges for obtaining representative measures of T-1 for process optimization and device screening. These T-1 fluctuations are often attributed to time varying coupling of the qubit to defects, putative two level systems (TLSs). In this work, we develop a technique to probe the spectral and temporal dynamics of T-1 in single junction transmons by repeated T-1 measurements in the frequency vicinity of the bare qubit transition, via the AC-Stark effect. Across 10 qubits, we observe strong correlations between the mean T-1 averaged over approximately nine months and a snapshot of an equally weighted T-1 average over the Stark shifted frequency range. These observations are suggestive of an ergodic-like spectral diffusion of TLSs dominating T-1, and offer a promising path to more rapid T-1 characterization for device screening and process optimization.

Automated summary

Superconducting qubits, as a leading candidate for quantum computing, exhibit fluctuations in their energy relaxation times (T-1), which can cause instabilities in device performance. This study introduces a technique to probe the spectral and temporal dynamics of T-1 and discovers strong correlations between the mean T-1 and a snapshot of T-1 over a specific frequency range, offering a promising approach for rapid T-1 characterization.