Design of realistic switches for coupling superconducting solid-state qubits

Superconducting flux qubits are a promising candidate for solid-state quantum computation. One of the reasons is that implementing a controlled coupling between the qubits appears to be relatively easy, if one uses tunable Josephson junctions. We evaluate possible coupling strengths and show, how much extra decoherence is induced by the subgap conductance of a tunable junction. In the light of these results, we evaluate several options of using intrinsically shunted junctions and show that based on available technology, Josephson field effect transistors and high-Tc junctions used as pi-shifters would be a good option, whereas the use of magnetic junctions as pi-shifters severely limits quantum coherence.