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This research introduces a novel spectroscopy technique to map the structured noise environment of superconducting qubits, specifically isolating long-lived two-level systems that induce non-Markovian dynamics. By reconstructing the full noise power spectral density and separating quantum from classical noise components, the study identifies hidden roadblocks that degrade gate fidelity over multiple operation cycles. These findings are critical for advancing fault-tolerant quantum computation by enabling protocols to bypass intrinsic environmental memory effects.
Quantum environment afterglow from broadband excitation spectroscopy in superconducting qubits
arXiv:2609.31280v1 Announce Type: new Abstract: Understanding the qubit environment is central to fault-tolerant superconducting quantum computation. Characterization typically relies on relaxation, leaving excitation largely underexplored. Here, we access this information with time-resolved broadband excitation spectroscopy. The resulting qubit excitation spectrum reveals a highly structured landscape, interspersed with cold regions. Combined with postselection, this technique enables full reconstruction of the noise power spectral density (PSD) and separates quantum from classical noise. With feed-forward, it exposes long-lived two-level-systems (TLSs), whose relaxation times span tens of microseconds to milliseconds - uncovering an intrinsic link between the qubit-TLS coupling and TLS relaxation. The data suggest that the long-lived TLSs are intrinsic to the qubit environment, and can cause excitation that lasts for many qubit operation cycles. Consequently, the environment retains a memory of prior dynamics, and properties like gate fidelity become non-Markovian and protocol-dependent. The presented approach enables identifying and bypassing the hidden roadblocks formed by long-lived TLSs in fault-tolerant quantum computation.
Authors:J. R. Guimarães, Y. Liu, Y. Gao, Y. Haddad, A. Galicia, D. A. Volkov, J. T. Schmieder, H. Bhardwaj, M. Neis, J. Cereijo, M. Jerger, P. A. Bushev, R. Barends
Abstract:Understanding the qubit environment is central to fault-tolerant superconducting quantum computation. Characterization typically relies on relaxation, leaving excitation largely underexplored. Here, we access this information with time-resolved broadband excitation spectroscopy. The resulting qubit excitation spectrum reveals a highly structured landscape, interspersed with cold regions. Combined with postselection, this technique enables full reconstruction of the noise power spectral density (PSD) and separates quantum from classical noise. With feed-forward, it exposes long-lived two-level-systems (TLSs), whose relaxation times span tens of microseconds to milliseconds - uncovering an intrinsic link between the qubit-TLS coupling and TLS relaxation. The data suggest that the long-lived TLSs are intrinsic to the qubit environment, and can cause excitation that lasts for many qubit operation cycles. Consequently, the environment retains a memory of prior dynamics, and properties like gate fidelity become non-Markovian and protocol-dependent. The presented approach enables identifying and bypassing the hidden roadblocks formed by long-lived TLSs in fault-tolerant quantum computation.
Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
arXiv:2609.31280 [quant-ph]
(or arXiv:2609.31280v1 [quant-ph] for this version)
https://doi.org/10.48550/arXiv.2609.31280 arXiv-issued DOI via DataCite (pending registration)
From: Jéferson Ribeiro Guimarães J. R. G. [view email] [v1] Fri, 25 Sep 2026 13:52:16 UTC (998 KB)
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