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Quantum Channel Transposition Now Possible with Just One Measurement, Research Confirms

Researchers at HKUST Guangzhou have mapped the physical realizability hierarchy of quantum channel transformations, showing that the transpose can be implemented exactly with a single query using a post‑selected teleportation protocol. In contrast, they prove that the complex conjugate and adjoint cannot be realized by any completely positive supermap, even probabilistically. To bypass this, the team introduces an optimal virtual protocol based on quasi‑probability decomposition, which also enables a more efficient estimator for expectation values of the Petz recovery map. The new estimator cuts query complexity from O(d^5.5…) to O(d^4…) for unital channels.