Model for1/fFlux Noise in SQUIDs and Qubits

We propose a model for $1/f$ flux noise in superconducting devices ($f$ is frequency). The noise is generated by the magnetic moments of electrons in defect states which they occupy for a wide distribution of times before escaping. A trapped electron occupies one of the two Kramers-degenerate ground states, between which the transition rate is negligible at low temperature. As a result, the magnetic moment orientation is locked. Simulations of the noise produced by randomly oriented defects with a density of $5\times {10}^{17}{\mathrm{m}}^{-2}$ yield $1/f$ noise magnitudes in good agreement with experiments.