2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/105694Decoherence of Josephson qubits can be substantially reduced by tuning their parameters to optimal operation points, with only quadratic coupling to fluctuations. We analyze dephasing due to 1/f noise for a two-level system, detuned from an optimal point, i.e., the crossover to the linear-coupling regime, both for free induction decay and for spin-echo experiments. Influence of several noise sources is also discussed.4 pages, 1 figure, accepted for publication in JETP LettMesoscale and Nanoscale Physicstext