- Accepted Paper
Metrological channels induced by encrypted quantum cloning: Optimal-probe Fisher-information broadcasting and single-use operational recovery
Phys. Rev. A - Accepted 13 October, 2026
DOI: https://doi.org/10.1103/zmbh-l8zk
Phys. Rev. A - Accepted 13 October, 2026
DOI: https://doi.org/10.1103/zmbh-l8zk
Encrypted quantum cloning creates multiple individually inaccessible signal systems from which an unknown input state can be recovered by combining any selected signal with a shared quantum key. Here we study parameter estimation when a local sensing transformation is applied after encrypted cloning and before decryption. For the two-clone qubit protocol, a local Pauli rotation on one encrypted signal is shown to induce, after standard decryption, a parameter-dependent Pauli dephasing channel rather than a unitary rotation. We derive its Pauli-transfer representation and the corresponding quantum Fisher information (QFI) for arbitrary mixed qubit probes. We then distinguish raw QFI, which for an optimal decoded probe may remain simultaneously present in a decoded output and its complement, from decoder-accessible QFI, which is operationally single-use because a first decryption destroys the shared syndrome information needed for a second standard recovery. For encrypted clones, the effective channel family is independent of clone number up to a clone-parity-dependent permutation of the Pauli axes (the single-clone case is exceptional for -sensing, where the decoded map stays unitary). This produces a metrological parity switch: for fixed probe and generator, even and odd clone numbers can yield respectively vanishing and maximal QFI. Closed expressions are obtained for the degradation of this parity contrast under probe depolarization and Pauli-diagonal Bloch-vector contraction.
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