A practical approach to calculating magnetic Johnson noise for precision measurements

TL;DR

This paper presents a practical method combining the fluctuation-dissipation theorem with finite element analysis to accurately calculate magnetic Johnson noise for complex geometries in precision magnetometry.

Contribution

It introduces a comprehensive approach that extends magnetic Johnson noise calculations to arbitrary geometries and detector shapes, enhancing precision measurement analysis.

Findings

The method accurately predicts magnetic Johnson noise for various geometries.

It can be applied to detectors with complex shapes like loops and gradiometers.

Physics insights from the method improve understanding of thermal magnetic noise.

Abstract

Magnetic Johnson noise is an important consideration for many applications involving precision magnetometry, and its significance will only increase in the future with improvements in measurement sensitivity. The fluctuation-dissipation theorem can be utilized to derive analytic expressions for magnetic Johnson noise in certain situations. But when used in conjunction with finite element analysis tools, the combined approach is particularly powerful as it provides a practical means to calculate the magnetic Johnson noise arising from conductors of arbitrary geometry and permeability. In this paper, we demonstrate this method to be one of the most comprehensive approaches presently available to calculate thermal magnetic noise. In particular, its applicability is shown to not be limited to cases where the noise is evaluated at a point in space but also can be expanded to include cases where the magnetic field detector has a more general shape, such as a finite size loop, a gradiometer, or a detector that consists of a polarized atomic species trapped in a volume. Furthermore, some physics insights gained through studies made using this method are discussed