arXiv:0712.0838 · Physical Review Letters

Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling

R. Harris, Mark W. Johnson, Siyuan Han, A. J. Berkley, J. Johansson, P. Bunyk, E. Ladizinsky, S. A. Govorkov, M. C. Thom, Sergey V. Uchaikin, Bruce Bumble, A. Fung, Anupama B. Kaul, Alan W. Kleinsasser, M. H. S. Amin, D. V. Averin

Published Sep 10, 2008• 81 citations

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Abstract

Macroscopic resonant tunneling between the two lowest lying states of a bistable rf SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian-shaped profile that is not peaked at the resonance point but is shifted to a bias at which the initial well is higher than the target well. The rms amplitude of the noise, which is proportional to the dephasing rate 1/tauphi, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low energy flux noise in this device is a quantum mechanical environment in thermal equilibrium.

DOI: 10.1103/physrevlett.101.117003

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