We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1Hz. Comparison of noise taken at positive and negative bias of a phase qubit shows the dominant noise source to be flux noise and not junction critical-current noise, with a magnitude similar to that measured previously in other systems. Theoretical calculations show that the level of flux noise is not compatible with the standard model of noise from two-level state defects in the surface oxides of the films.
@article{arxiv.0708.2125,
title = {1/f Flux Noise in Josephson Phase Qubits},
author = {Radoslaw C. Bialczak and R. McDermott and M. Ansmann and M. Hofheinz and N. Katz and Erik Lucero and Matthew Neeley and A. D. O'Connell and H. Wang and A. N. Cleland and John M. Martinis},
journal= {arXiv preprint arXiv:0708.2125},
year = {2009}
}