Materials Physics and Quantum Coherence in Superconducting Qubits

Nonidealities of real superconductors in the form of residual rf losses and conductance below the superconducting energy gap in tunneling Josephson junctions are discussed as possible sources of decoherence in Josehphson junction flux qubits. The purpose of the paper is pedagogical and aimed at taking a first step in a unified view of the quantum behavior of superconducting qubits and the realities of the materials out of which they are constructed. The need for a dialog between the quantum physicist and the materials physicist is stressed. Residual rf losses and localized states in junction barriers are identified as important subjects for this dialog.