Topological degeneracy and decoherence-protected qubits in circuit QED
  We introduce an extended Dicke model with controllable long-range atom-atom interaction to simulate topologically ordered states and achieve decoherence-protected qubits. We illustrate our idea in an experimentally feasible circuit quantum electrodynamics scenario. Due to the intrinsic competition with the atom-field coupling strength, we first demonstrate that this atom-atom interaction can exhibit a novel topological quantum interference effect arising from the instanton and anti-instanton tunneling paths. As a consequence, this proposed model only with a few odd-number of atoms has a two-fold absolute degenerate ground-subspace with a large energy gap, which can become larger with the increasing of the system-size. It may also support the excitation of anyonic statistics, and thus can be regarded as a possible candidate for processing topological quantum memory. 
Gang Chen, Zheng-Yuan Xue, J.-Q. Liang