Qubit decoherence by Gaussian low-frequency noise

We have derived explicit non-perturbative expression for decoherence of quantum oscillations in a qubit by Gaussian low-frequency noise. Decoherence strength is controlled by the noise spectral density at zero frequency while the noise correlation time $\tau$ determines the time $t$ of crossover from the $1/\sqrt{t}$ to the exponential suppression of coherence. We also performed Monte Carlo simulations of qubit dynamics with noise which agree with the analytical results.