Two-qubit gate operations in superconducting circuits with strong   coupling and weak anharmonicity
  We investigate theoretically the implementation of two-qubit gates in a system of two coupled superconducting qubits. In particular, we analyze two-qubit gate operations under the condition that the coupling strength is comparable to or even larger than the anharmonicity of the qubits. By numerically solving the time-dependent Schr\"odinger equation, we obtain the dependence of the two-qubit gate fidelity on the system parameters in the case of direct and indirect qubit-qubit coupling. Our numerical results can be used to identify the "safe" parameter regime for experimentally implementing two-qubit gates with high fidelity in these systems. 
Xin-You L\"u, S. Ashhab, Wei Cui, Rebing Wu, and Franco Nori
quant-ph cond-mat.supr-con