Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Transport: Poster Session

TT 22.23: Poster

Wednesday, February 27, 2008, 14:00–18:00, Poster B

Modeling of quasiparticle transitions in Josephson charge-phase qubits — •Jens Könemann, Hermann Zangerle, Brigitte Mackrodt, Ralf Dolata, and Alexander B. Zorin — Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany

Superconducting circuits, based on the tunneling of single Cooper pairs, enable remarkable charge-phase qubits. The qubit operation relies on the coherent superposition of the macroscopic quantum states, but the unwanted tunneling of unpaired electrons (quasiparticles) changes instantly the charge state and thus, the working point of the qubit.

Recently we have investigated quasiparticle transitions in an Al charge-phase qubit [1] inducing a dynamic change of the qubit states. Non-equilibrium quasiparticles tunnel stochastically on and off the island and may excite the qubit. The relaxation of the qubit by releasing a single quasiparticle to the leads becomes the dominating relaxation mechanism. In this work, we present a numerical modeling of these transitions. Moreover, we discuss the effect of microwave irradiation on the quasiparticle-induced transitions.
[1] J. Könemann et al., Phys. Rev. B 76, 134507 (2007).