Macroscopic quantum tunneling in image Josephson junctions with insulating ferromagnets and its application to phase qubits

We theoretically investigate macroscopic quantum tunneling (MQT) in a current-biased π junction with a superconductor (S) and an insulating ferromagnet (IF). By using the functional integral method and the instanton approximation, the influence of the quasiparticle dissipation on MQT is found to be very weak. This feature makes it possible to realize a quantum information devices with high coherency. We also discuss how to make use of S–IF–S π junctions in the construction of a phase qubit.