1/f Flux noise in Josephson phase qubits

Phys Rev Lett. 2007 Nov 2;99(18):187006. doi: 10.1103/PhysRevLett.99.187006. Epub 2007 Nov 2.


We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1 Hz. A comparison of the 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.