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

TL;DR

This paper derives a form of the fluctuation-dissipation theorem for resistively shunted Josephson junction arrays, linking flux noise spectrum to the array's impedance and analyzing detection coil effects.

Contribution

It introduces a new derivation of the fluctuation-dissipation theorem that explicitly accounts for screening effects in Josephson junction arrays.

Findings

Flux noise power spectrum expressed in terms of frequency-dependent impedance.

Relation between noise amplitude and detection coil parameters analyzed.

Provides a theoretical framework for understanding flux noise in Josephson arrays.

Abstract

The form of the fluctuation-dissipation theorem for a resistively shunted Josephson juction array is derived with the help of the method which explicitely takes into acoount screening effects. This result is used to express the flux noise power spectrum in terms of frequency dependent sheet impedance of the array. The relation between noise amplitude and parameters of the detection coil is analysed for the simplest case of a single-loop coil.