Andreev spin-noise detector

TL;DR

This paper explores using magnetic Josephson junctions as sensitive detectors for magnetic noise, especially near the 0- transition, with potential divergence in sensitivity at zero temperature.

Contribution

It demonstrates how magnetic Josephson junctions can be employed as highly sensitive magnetic noise detectors, highlighting the enhanced sensitivity near the 0- transition and the conditions isolating magnetic noise effects.

Findings

Sensitivity diverges at the 0- transition at zero temperature.

Magnetic noise can be isolated from other noise sources in the quantum dot system.

The junction's response is strongly enhanced under specific magnetic field conditions.

Abstract

We investigate the possibility to employ magnetic Josephson junctions as magnetic-noise detectors. To illustrate our idea, we consider a system consisting of a quantum dot coupled to superconducting leads in the presence of an external magnetic field. Under appropriate assumptions, we relate the noise in the Josephson current to magnetization noise. At the magnetic field driven $0-\pi$ transition the junction sensitivity as magnetic noise detector is strongly enhanced and it diverges in the zero temperature limit. Moreover, we demonstrate that, if also dot energy is affected by fluctuations, only the magnetic noise channel contributes to Josephson current noise response when the quantum dot is tuned in resonance with superconducting leads.