Diagonal Unitary Covariant Superchannels

• URL: http://arxiv.org/abs/2512.24389v2
• Date: Tue, 06 Jan 2026 18:42:21 GMT
• Title: Diagonal Unitary Covariant Superchannels
• Authors: Dariusz Chruściński, Vivek Pandey, Sohail,
• Abstract summary: We present a complete characterization of diagonal unitary covariant (DU-covariant) superchannels.<n>The presented framework unifies and extends known families of covariant quantum channels.<n>Results provide a practical toolbox for symmetry-restricted higher-order quantum processes.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We present a complete characterization of diagonal unitary covariant (DU-covariant) superchannels, i.e. higher-order transformations transforming quantum channels into themselves. Necessary and sufficient conditions for complete positivity and trace preservation are derived and the canonical decomposition describing DU-covariant superchannels is provided. The presented framework unifies and extends known families of covariant quantum channels and enables explicit analysis of their action on physically relevant examples, including amplitude-damping, bit-flip, and Pauli channels. Our results provide a practical toolbox for symmetry-restricted higher-order quantum processes and offer a setting for exploring open problems such as the celebrated PPT$^2$ conjecture.

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