  Several designs of inter-qubit coupling are considered. It is shown that by a
combination of Josephson and capacitive coupling one can realize qubit
interactions of variable spin content. Qubit arrays are discussed as models of
quantum spin chains. In particular, a qubit model of the 1D quantum Ising spin
chain is proposed. A realization of unpaired Majorana fermion states in this
system is considered. It is shown that Majorana states are represented by spin
flip excitations localized on the chain ends. Using unpaired Majorana states in
qubit chains for decoherence protected quantum computing is discussed.
