2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/166943A theory of dynamical control by modulation for optimal decoherence reduction is developed. It is based on the non-Markovian Euler-Lagrange equation for the energy-constrained field that minimizes the average dephasing rate of a qubit for any given dephasing spectrum.6 pages, including 2 figures and an appendixQuantum Physicstext