Systematic Characterization of Transmon Qubit Stability with Thermal Cycling

TL;DR

This study longitudinally characterizes 27 transmon qubits over a year and four thermal cycles, revealing stable device parameters but stochastic environmental changes, emphasizing the need for recalibration in quantum processors.

Contribution

It provides a comprehensive analysis of qubit stability across thermal cycles, highlighting the impact of environmental variables and introducing a spectral topography fidelity metric.

Findings

Device parameters remain stable after thermal cycling.

Environmental variables show stochastic reconfiguration after each cycle.

Thermal cycling acts as a 'hard reset' for local defect environments.

Abstract

The temporal stability and reproducibility of qubit parameters are critical for the long-term operation and maintenance of superconducting quantum processors. In this work, we present a comprehensive longitudinal characterization of 27 frequency-tunable transmon qubits spanning over one year across four thermal cycles. Our results establish a distinct hierarchy of stability for superconducting hardware. We find that the intrinsic device parameters determining the qubit frequency and the baseline energy relaxation times ($T_1$) exhibit high robustness against thermal stress, characterized by frequency deviations typically confined within 0.5\% and non-degraded coherence baselines. In stark contrast, the environmental variables, specifically the background magnetic flux offsets and the microscopic landscape of two-level system (TLS) defects, undergo a significant stochastic reconfiguration after each cycle. By employing frequency-dependent relaxation spectroscopy and a quantitative metric, the $T_1$ Spectral Topography Fidelity, we demonstrate that thermal cycling acts as a ``hard reset'' for the local defect environment. This process introduces a level of spectral randomization equivalent to thousands of hours of continuous low-temperature evolution. These findings confirm that while the fabrication quality is preserved, the specific noise realization is statistically distinct for each thermal cycle, necessitating automated recalibration strategies for large-scale quantum systems.