Energy Decay in Josephson Qubits from Non-equilibrium Quasiparticles | NIST

M. Lenander, H. Wang, R. Bialczek +11 more

Yvonne Y. Gao, Chen Wang, Ioan M. Pop +9 more

Max Hays, Kyle Serniak, G. de Lange +10 more

Kyle Serniak, Max Hays, G. de Lange +10 more

John M. Martinis, M. Ansmann, José Aumentado

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 predictions based on a prior measurement of the quasiparticle density n_qp = 10/um^3, which suggests that non-equilibrium quasiparticles are an important decoherence source for Josephson qubits. Calculations of the energy-decay and diffusion of quasiparticles also indicate 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.

John M. Martinis

A calculation of the energy decay rate of a Josephson qubit from non-equilibrium quasiparticles is made using the environmental P(E) theory. For a large-capacitance qubit, we extend the theory to include the tunneling of quasiparticles, which has an electron- and hole-like charge components.