Dynamics of superconducting qubit relaxation

Abstract

Single junction transmon qubits are a leading candidate for quantum computing, in part, because of their robustness to charge and flux noise. However, they display large temporal fluctuations in their energy relaxation times T1. This introduces challenges to the stability of multi-qubit device performance. Furthermore, averaging over days or weeks can also be necessary to obtain representative measures of T1 for process optimization and device screening. These T1 fluctuations are typically attributed to resonant couplings of the qubit to two level systems (TLS). In this work, we probe the spectral and temporal dynamics of T1 in single junction transmons by measurements of relaxation probabilities at AC-Stark shifted frequencies around the bare transition. Across 10 qubits, we observe strong correlations between the relaxation probability averaged around the bare qubit frequency, and mean T1 averaged over several months. This suggests that the qubits sample an ergodic-like spectral diffusion of the nearby TLSs and that the long-time average T1 might be estimated rapidly from a snapshot of its frequency dependence.