Reducing defects in Josephson phase qubits -- interdigitated capacitors and microbridges

Josephson phase qubits have recently demonstrated increased coherence times, setting them as a serious option for scalable quantum computing. This has been made possible by identifying dielectric two-level defect states in the Josephson junction and in any additional capacitance in the circuit as a major source of decoherence. We show that by fabricating an external, high quality interdigitated capacitor the lifetime of the qubit is increased to at least half a microsecond. Further reduction in decoherence is expected by completely removing the dielectric of the tunnel junction and replacing it with a superconducting microbridge. Some preliminary results for MBE grown Rhenium microbridge qubits will be presented.