Dephasing of Solid-State Qubits at Optimal Points

Abstract

Motivated by recent experiments with Josephson-junction circuits, we analyze the influence of various noise sources on the dynamics of two-level systems at optimal operation points where the linear coupling to low-frequency fluctuations is suppressed. We study the decoherence due to nonlinear (quadratic) coupling, focusing on the experimentally relevant $1/f$ and Ohmic noise power spectra. For $1/f$ noise strong higher-order effects influence the evolution.