Adaptive Spectroscopy of Fast Two-Level-System Dynamics in Superconducting Qubits

2026/08/03 by Fabrizio Berritta, David Pahl, Lukas Pahl +15
Physics and Astronomy · #quant-ph #cond-mat.mes-hall

paper · pdf

8 pages, 3 figures; Supplemental Material: 12 pages, 10 figures

arxiv created 2026/08/03 · arxiv updated 2026/08/04

Abstract

Parasitic two-level-system (TLS) defects are a major source of energy relaxation and temporal instability in superconducting quantum processors. Our sub-second adaptive spectroscopy reveals telegraphic switching of TLSs with a characteristic timescale of a few seconds and spectral diffusion with diffusivity D ≈ 0.9~MHz²/s. These timescales are about 3 × 10² times faster than what is observed in conventional nonadaptive spectroscopy, which typically requires hours of measurement time. We resolve such fast dynamics on a field-programmable gate array (FPGA)-based controller that enables measurement of frequency- and time-resolved relaxations with sub-second temporal resolution in flux-tunable superconducting qubits. We observe similar defect dynamics across multiple qubits in independently fabricated devices measured in different laboratories. We correlate TLS-induced fluctuations with gate-level errors using randomized benchmarking. Our results reveal a previously inaccessible regime of frequency-resolved TLS dynamics and redefine the timescales relevant to TLS-aware characterization and calibration of superconducting quantum processors.

Citations

• Mapping the positions of Two-Level-Systems on the surface of a superconducting transmon qubit
• A multi-dimensional quantum estimation and model learning framework based on variational Bayesian inference
• Real-time adaptive tracking of fluctuating relaxation rates in superconducting qubits
• Statistics of Strongly Coupled Defects in Superconducting Qubits
• Inferring charge noise source locations from correlations in spin qubits
• Performance Stabilization of High-Coherence Superconducting Qubits
• Scalable and Site-Specific Frequency Tuning of Two-Level System Defects in Superconducting Qubit Arrays
• Efficient Qubit Calibration by Binary-Search Hamiltonian Tracking
• Snakes and Ladders: Adapting the surface code to defects
• Detrimental non-Markovian errors for surface code memory
• Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes
• Error mitigation with stabilized noise in superconducting quantum processors
• Noise Correlations in a 1D Silicon Spin Qubit Array
• Passive and active suppression of transduced noise in silicon spin qubits
• Material matters in superconducting qubits
• Dynamics of superconducting qubit relaxation times
• Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
• Circuit Quantum Electrodynamics
• On Gibbs sampling for state space models
• A tutorial on hidden Markov models and selected applications in speech recognition
• A Maximization Technique Occurring in the Statistical Analysis of Probabilistic Functions of Markov Chains