• Accepted Paper

Encrypted cloning of qubits is able to serve as a quantum primitive, already on non-error-corrected quantum hardware

Koji Yamaguchi, Leon Rullkötter, Ibrahim Shehzad, Sean J. Wagner, Christian Tutschku, and Achim Kempf

Phys. Rev. Research - Accepted 27 October, 2026

DOI: https://doi.org/10.1103/872f-l3wm

Abstract

The no-cloning theorem forbids the creation of identical copies of qubits, thereby imposing strong limitations on quantum technologies. A recently-proposed protocol, , showed, however, that the creation of perfect clones is theoretically possible - if the clones are simultaneously encrypted with a single-use decryption key. It has remained an open question, however, whether encrypted cloning is viable as a practical quantum primitive on real, noisy hardware. Here, we settle this question by implementing encrypted cloning on IBM Heron-R2 superconducting processors using up to 154 qubits. We find that the decrypted clones on present-day hardware exceed the entanglement-fidelity ceiling of the optimal universal cloning machine and violate the CHSH inequality, which the optimal approximate cloner cannot do even without any noise. Moreover, encrypted cloning is stable under hardware noise, even when used as a module, namely in parallel, in series or interleaved, while preserving pre-existing entanglement. These results establish encrypted cloning as a versatile quantum primitive for practical use, and they necessitate a further refinement to our understanding of the no-cloning theorem: quantum information can be cloned - in theory perfectly, and in practice with merely the depth-governed fidelity decay of the hardware - if encrypted or obscured with a single-use decryption mechanism.

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