The energy of the ground state (a) and the transition energy hf01 of the twin qubit calculated from the Hamiltonian of Eq. (1) (b). The parameters α?=?0.72 and C?=?5.2 fF and the Josephson energy is E J ?=?50?GHz. These dependencies are Φ0 periodic and symmetric with respect to Φ/Φ0?=?0.5. The minimum point of the (b) plot corresponds to the transition of the central junction phase φ0 from zero to π.