L.B. Ioffe, M.V. Feigel`man, and B. Douçot, Topologically protected quantum states and quantum computing in Josephson junctions arrays: Сверхпроводимость и мезоскопические структуры, Low Temp. Phys. 30, (2004) [Fiz. Nizk. Temp. 30, 841-855, (2004)] DOI: https://doi.org/10.1063/1.1789936.