2005/07/13 by P. Bertet, Bertet, P., I. Chiorescu +5
Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Superconductivity (cond-mat.supr-con) #cond-mat.mes-hall #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.cond-mat/0507290
arxiv created 2005/07/13 · arxiv updated 2009/12/01
Decoherence in superconducting qubits is known to arise because of a variety of environmental degrees of freedom. In this article, we focus on the influence of thermal fluctuations in a weakly damped circuit resonance coupled to the qubit. Because of the coupling, the qubit frequency is shifted by an amount n δν0 if the resonator contains n energy quanta. Thermal fluctuations induce temporal variations n(t) and thus dephasing. We give an approximate formula for the qubit dephasing time as a function of δν0. We discuss the specific case of a flux-qubit coupled to the plasma mode of its DC-SQUID detector. We first derive a plasma mode-qubit interaction hamiltonian which, in addition to the usual Jaynes-Cummings term, has a coupling term quadratic in the oscillator variables coming from the flux-dependence of the SQUID Josephson inductance. Our model predicts that δν0 cancels in certain non-trivial bias conditions for which dephasing due to thermal fluctuations should be suppressed.