We calculate the energy decay rate of Josephson qubits and superconducting resonators from non-equilibrium quasiparticles. The decay rates from experiments are shown to be consistent with our predictions based on a prior measurement of the quasiparticle density, which suggests that non-equilibrium quasiparticles is an important decoherence mechanism for Josephson qubits. Calculations of the energy-decay and diffusion of quasiparticles also indicates that prior engineered gap and trap structures, which reduce the density of quasiparticles, should be redesigned to improve their efficacy. This model also explains a striking feature in Josephson qubits and resonators - a small reduction in decay rate with increasing temperature.
Citation: Physical Review Letters
Pub Type: Journals
Superconductivity, Josephson junctions, quantum computing, qubits