Josephson junction materials research using phase qubits

Abstract

At present, the performance of superconducting qubits is limited by decoherence. Strong decoherence of phase qubits is associated with spurious microwave resonators residing within the Josephson junction tunnel barrier.1 In this Chapter three different fabrication techniques for producing tunnel junctions that vary the properties of the superconductor-insulator interface are investigated. Through experimental measurements, the junction and corresponding qubit quality is characterized. A strong correlation between the morphology of oxidized base electrodes and the lowering of subgap currents in the junction I-V characteristics is found, while there is no noticeable improvement in the performance of fabricated phase qubits. Thus, traditional indicators of junction performance may not be enough to determine qubit performance. However, truly crystalline insulating barriers may be the key to improving Josephson junction based qubits. © 2006 Springer Science+Business Media, Inc.