Noise of a superconducting magnetic flux sensor based on a proximity Josephson junction

TL;DR

This paper presents measurements of flux noise in a superconducting magnetometer based on a proximity Josephson junction, demonstrating its potential for sensitive, low-dissipation magnetic sensing and noise analysis.

Contribution

The study introduces a method to measure flux noise in a SQUIPT device using a cryogenic amplifier, highlighting its capabilities and avenues for optimization.

Findings

Achieved flux noise of ~4 μΦ₀/Hz^{1/2} in a non-optimized device

Flux noise limited by shot noise of the probe tunnel junction

Setup can be used to investigate shot noise in high-impedance nonlinear devices

Abstract

We demonstrate simultaneous measurements of DC transport properties and flux noise of a hybrid superconducting magnetometer based on the proximity effect (superconducting quantum interference proximity transistor, SQUIPT). The noise is probed by a cryogenic amplifier operating in the frequency range of a few MHz. In our non-optimized device, we achieve minimum flux noise $\sim 4\;\mu\Phi_0/Hz^{1/2}$, set by the shot noise of the probe tunnel junction. The flux noise performance can be improved by further optimization of the SQUIPT parameters, primarily minimization of the proximity junction length and cross section. Furthermore, the experiment demonstrates that the setup can be used to investigate shot noise in other nonlinear devices with high impedance. This technique opens the opportunity to measure sensitive magnetometers including SQUIPT devices with very low dissipation.