Decoherence benchmarking of superconducting qubits

By J. Burnett, A. Bengtsson, M. Scigliuzzo, D. Niepce, M. Kudra, Per Delsing, J. Bylander. npj Quantum Information, 2019

377 citations recorded by the source corpus.

We benchmark the decoherence of superconducting transmon qubits to examine the temporal stability of energy relaxation, dephasing, and qubit transition frequency. By collecting statistics during measurements spanning multiple days, we find the mean parameters T1¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline {T_1}$$\end{document} = 49 μs and T2*¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline {T_2^ \ast }$$\end{document} = 95 μs; however, both of these quantities fluctuate, explaining the need for frequent re-calibration in qubit setups. Our main finding is that fluctuations in qubit relaxation are local to the qubit and are caused by instabilities of near-resonant two-level-systems (TLS). Through statistical analysis, we determine sub-millihertz switching rates of these TLS and observe the coherent coupling between an individual TLS and a transmon qubit. Finally, we find evidence that the qubit’s frequency stability produces a 0.8 ms limit on the pure dephasing which we also observe. These findings raise the need for performing qubit metrology to examine the reproducibility of qubit parameters, where these fluctuations could affect qubit gate fidelity.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics, Condensed Matter Physics

View Paper: https://www.semanticscholar.org/paper/19e362a3938f9abb1cd81dcc3834d4da16452615

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Citations in the corpus

Materials challenges and opportunities for quantum computing hardware (2021, background): “Slow charge background drift or TLS behavior in the vicinity of a quantum dot can also hinder sensitive charge stability measurements ( 176 ) and limit coherence times.”
Observation of separated dynamics of charge and spin in the Fermi-Hubbard model (2020, background): “Temporal instabilities, including drifts and fluctuations in the control fields and qubit frequencies [51–58], can propagate and accumulate coherently in large quantum circuits.”
Oscillating bound states for a giant atom (2019, background): “[61] J.”
Systematic improvements in transmon qubit coherence enabled by niobium surface encapsulation (2023, neutral): “The ﬂ uctuations of T 1 overtime[showninFig.3e],anditsGaussiandistribution[showninFig.3f] havebothbeenobservedinliterature 4,35 , and are presumably considered a signature of qubit lifetime limited by TLS defects residing in the materials.”