Abstract
Quantum error correction (QEC) codes are necessary to fault-tolerantly operate quantum computers. However, every such code is inherently limited by its inability to detect logical errors. Here, we propose and implement a method that leverages dynamical decoupling (DD) to drastically suppress logical errors. The key to achieving this is to use the normalizer elements of the QEC code as DD pulses, which we refer to as normalizer dynamical decoupling (NDD). The resulting hybrid QEC-NDD strategy is in principle capable of handling arbitrary weight errors. We test an error detecting version of this strategy using IBM transmon devices and the [[4, 2, 2]] code, demonstrating performance that significantly exceeds the capabilities of using either this code or DD in isolation. We present a method that allows for the detection of logical errors affecting logically encoded Bell states, which, in this case, arise primarily from crosstalk among physical qubits. Building on this, we experimentally demonstrate high-fidelity entangled logical qubits. The fidelities we achieve are beyond-breakeven, i.e., they significantly exceed the corresponding fidelities of unprotected entangled qubits in the same setting.
Data availability
All data are available from the corresponding authors upon request.
Code availability
Qiskit experiments and analysis codes that support the findings of this study are available from the corresponding authors upon request.
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Acknowledgements
This material is based upon work supported by, or in part by, the Intelligence Advanced Research Projects Activity (IARPA), under the Entangled Logical Qubits program through Cooperative Agreement Number W911NF23-2-0216, by the U.S. Army Research Laboratory and the U.S. Army Research Office under contract/grant number W911NF2310255, and by the Defense Advanced Research Projects Agency under Agreement HR00112230006. The views, opinions and/or findings expressed are those of the author(s) and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government. This research was conducted using IBM Quantum Systems provided through the University of Southern California’s IBM Quantum Innovation Center. The views expressed are those of the authors and do not reflect the official policy or position of IBM or the IBM Quantum team.
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A.V. and D.A.L. conceived the project. A.V. designed and performed the experiments. A.V., V.T., M.M.-O., and D.A.L. analyzed the data and results. V.T. designed the robust structure of sequences. M.M.-O., V.K., F.B., and D.A.L. designed and constructed the definitions and proofs of the theorems. All authors contributed to the writing of the manuscript.
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Vezvaee, A., Tripathi, V., Morford-Oberst, M. et al. Demonstration of high-fidelity entangled logical qubits using transmons. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70011-3
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DOI: https://doi.org/10.1038/s41467-026-70011-3
