Decoherence in a superconducting flux qubit with a π -junction

Abstract

We consider the use of a π junction for flux qubits to realize degenerate quantum levels without external magnetic field. On the basis of the Caldeira-Leggett model, we derive an effective spin-Boson model and study decoherence of this type of qubits. We estimate the dephasing time by using parameters from recent experiments of superconductor-insulator-ferromagnet- superconductor junctions and show that high critical current and large subgap resistance are required for the π junction to realize a long coherent time. © 2007 The American Physical Society.