Fluctuation-dissipation theorem and flux noise in overdamped Josephson-junction arrays

The form of the fluctuation-dissipation theorem for a resistively shunted Josephson-junction array is derived with the help of the method which explicitly takes into account the screening effects. This result is used to express the flux noise power spectrum in terms of the frequency-dependent sheet impedance of the array. The relation between the noise amplitude and the parameters of the detection coil is analyzed for the simplest case of a single-loop coil, as well as the frequency dependence of the noise spectrum in different regimes.