# Systematic Characterization of Transmon Qubit Stability with Thermal Cycling

## TL;DR

This paper studies how thermal cycling affects the stability of transmon qubits in quantum processors over a year-long period.

## Contribution

The work introduces a systematic, longitudinal study of qubit stability across multiple thermal cycles, revealing distinct stability hierarchies in superconducting hardware.

## Key findings

- Intrinsic qubit parameters remain stable with frequency deviations under 0.5% across thermal cycles.
- Environmental variables like magnetic flux offsets and TLS defects show significant stochastic reconfiguration after each cycle.
- Thermal cycling resets the local defect environment, introducing spectral randomization equivalent to thousands of hours of low-temperature evolution.

## 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 (T1) 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 T1 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.