Positive- and negative-frequency noise from an ensemble of two-level fluctuators

作     者：Xinyuan You Aashish A. Clerk Jens Koch 

作者机构：Northwestern-Fermilab Center for Applied Physics and Superconducting Technologies Northwestern University Evanston Illinois 60208 USA Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA Pritzker School of Molecular Engineering University of Chicago 5640 South Ellis Avenue Chicago Illinois 60637 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA 

出 版 物：《Physical Review Research》 (Phys. Rev. Res.)

年 卷 期：2021年第3卷第1期

页      面：013045-013045页

核心收录：

基　　金：U.S. Army Research Office [W911NF-17-C-0024, W911NF-19-10328] Northwestern-Fermilab Center for Applied Physics and Superconducting Technologies 

主　　题：Open quantum systems & decoherence Quantum fluctuations & noise Quantum information with solid state qubits Josephson junctions Superconducting qubits Thin films 

摘      要：The analysis of charge noise based on the Bloch-Redfield treatment of an ensemble of dissipative two-level fluctuators generally results in a violation of the fluctuation-dissipation theorem. The standard Markov approximation (when applied to the two-level fluctuators coupled to a bath) can be identified as the main origin of this failure. The resulting decoherence rates only involve the bath response at the fluctuator frequency, and thus completely neglect the effects of frequency broadening. A systematic and computationally convenient way to overcome this issue is to employ the spectator-qubit method: by coupling an auxiliary qubit to the two-level fluctuator ensemble, an analytical approximation for S(ω) fully consistent with the fluctuation-dissipation theorem can be obtained. We discuss the resulting characteristics of the noise which exhibits distinct behavior over several frequency ranges, including a 1/f to 1/f2 crossover with a T3 temperature dependence of the crossover frequency.