2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/114518In this paper, we consider a simplified error-correcting problem: for a fixed encoding process, to find a cascade connected quantum channel such that the worst fidelity between the input and the output becomes maximum. With the use of the one-to-one parametrization of quantum channels, a procedure finding a suboptimal error-correcting channel based on a semidefinite programming is proposed. The effectiveness of our method is verified by an example of the bit-flip channel decoding.6 pages, no figure, Some notations differ from those in the PRA versionQuantum Physicstext