Magnetic noise around metallic microstructures

TL;DR

This paper analyzes the magnetic noise generated by metallic microstructures at finite temperature, highlighting polarization anisotropy effects and providing numerical estimates relevant for atom chip traps.

Contribution

It introduces numerical methods for calculating magnetic noise in arbitrary geometries and compares these with simple approximations, improving understanding of noise effects in microstructured metals.

Findings

Magnetic noise exhibits polarization anisotropy above finite-width wires.

Numerical calculations provide accurate estimates for loss and dephasing in atom chip traps.

Simple incoherent summation approximations qualitatively match numerics but miss current correlations.

Abstract

We compute the local spectrum of the magnetic field near a metallic microstructure at finite temperature. Our main focus is on deviations from a plane-layered geometry for which we review the main properties. Arbitrary geometries are handled with the help of numerical calculations based on surface integral equations. The magnetic noise shows a significant polarization anisotropy above flat wires with finite lateral width, in stark contrast to an infinitely wide wire. Within the limits of a two-dimensional setting, our results provide accurate estimates for loss and dephasing rates in so-called `atom chip traps' based on metallic wires. A simple approximation based on the incoherent summation of local current elements gives qualitative agreement with the numerics, but fails to describe current correlations among neighboring objects.