Quantum environment afterglow from broadband excitation spectroscopy in superconducting qubits
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.
Related
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- Entanglement-enhanced Ramsey spectroscopy of broadband signals
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BibTeX
@misc{guimaraes2026quantum,
title = {{Quantum environment afterglow from broadband excitation spectroscopy in superconducting qubits}},
author = {J. R. Guimarães and Y. Liu and Y. Gao and Y. Haddad and A. Galicia and D. A. Volkov and J. T. Schmieder and H. Bhardwaj and M. Neis and J. Cereijo and M. Jerger and P. A. Bushev and R. Barends},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31280},
eprint = {2609.31280},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31280},
}
RIS
TY - UNPB
TI - Quantum environment afterglow from broadband excitation spectroscopy in superconducting qubits
AU - J. R. Guimarães
AU - Y. Liu
AU - Y. Gao
AU - Y. Haddad
AU - A. Galicia
AU - D. A. Volkov
AU - J. T. Schmieder
AU - H. Bhardwaj
AU - M. Neis
AU - J. Cereijo
AU - M. Jerger
AU - P. A. Bushev
AU - R. Barends
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31280
UR - https://arxiv.org/abs/2609.31280
AB - 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.
ER -