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TT: Tiefe Temperaturen

TT 26: Transport - Poster Session

TT 26.17: Poster

Mittwoch, 29. März 2006, 14:30–18:30, P1

Phase-space theory for nonlinear detectors of superconducting qubits — •Ioana Serban and Frank Wilhelm — Department Physik. Arnold-Sommerfeld-Center for Theoretical Physics, and Center for Nanoscience, Ludwig-Maximilians-Universitaet, Theresienstr. 37 80333 Muenchen, Germany

Superconducting circuits are envisioned as quantum bits and demonstrate quantum-coherent features i.e. Rabi oscillations and Ramsey fringes. The detector (e.g. a superconducting quantum interference device) can itself be described by a Hamiltonian and treated quantum-mechanically.This allows more insights into the measurement process.

Several experimental groups have realized good detectors with strong coupling to the measured system, where nonlinear dynamics plays a significant role.

Motivated by the recent experiment [1], we study a nonlinear detector where the qubit couples to the square amplitude of a driven oscillator, which can be used for dispersive detection. We use a complex-environment approach treating the qubit and the oscillator exactly, expressing their full Floquet-state master equations in phase space. We investigate the backaction of the environment on the measured qubit and explore the resolution of measurement. We emphasize the resulting role of non-Gaussian and non-Markovian effects in the backaction including significant non-exponential shape of the coherence decay.

[1] A. Lupaşcu et al. PRL 93 177006 (2004)