We have analyzed quasiparticle transitions in an Al charge-phase qubit inducing a dynamic change of the qubit states. The time-averaged mixed state is related to the strong coupling of the qubit to an ensemble of non-equilibrium quasiparticles in the leads. Such quasiparticles tunnel stochastically on and off the island and can excite the qubit. Continuous monitoring of the qubit impedance at a frequency of 80 MHz shows the admixture of the excited state. We present a numerical description of these cyclic transitions and compare it with our experimental data.
@article{arxiv.0808.3080,
title = {Modeling of quasiparticle-induced excitations of a Josephson charge-phase qubit},
author = {J. Könemann and H. Zangerle and B. Egeling and R. Harke and B. Mackrodt and R. Dolata and A. B. Zorin},
journal= {arXiv preprint arXiv:0808.3080},
year = {2008}
}