Microscopic origin of low frequency flux noise in Josephson circuits

TL;DR

This paper investigates the microscopic origin of low frequency flux noise in superconducting circuits, attributing it to spins at the superconductor-insulator boundary influenced by RKKY interactions, explaining various observed noise characteristics.

Contribution

It proposes a microscopic model involving boundary spins and RKKY interactions that accounts for observed flux noise properties in Josephson circuits.

Findings

Explains size independence of flux noise.

Accounts for different spectral dependences in SQUIDs.

Matches observed noise intensity with realistic parameters.

Abstract

We analyze the data and discuss their implications for the microscopic origin of the low frequency flux noise in superconducting circuits. We argue that this noise is produced by spins at the superconductor insulator boundary whose dynamics is due to RKKY interaction. We show that this mechanism explains size independence of the noise, different frequency dependences of the spectra reported in large and small SQUIDs and gives the correct intensity for realistic parameters.