A micro-SQUID with dispersive readout for magnetic scanning microscopy

TL;DR

This paper presents a micro-SQUID with dispersive readout designed for low temperature magnetic scanning microscopy, featuring tunable resonance, integrated coils, and promising low flux noise performance.

Contribution

The authors introduce a novel micro-SQUID design with dispersive readout, tunable resonance, and integrated coils for enhanced magnetic microscopy at low temperatures.

Findings

Flux noise of 80 nΦ₀/Hz^{1/2} at 4 K

Potential reduction of flux noise to 30 nΦ₀/Hz^{1/2} at 100 mK

Resonance frequency tunable from 5 to 12 GHz

Abstract

We have designed and characterized a micro-SQUID with dispersive readout for use in low temperature scanning probe microscopy systems. The design features a capacitively shunted RF SQUID with a tunable resonance frequency from 5 to 12 GHz, micrometer spatial resolution and integrated superconducting coils for local application of magnetic fields. The SQUID is operated as a nonlinear oscillator with a flux- and power-dependent resonance frequency. Measurements for device characterization and noise benchmarking were carried out at 4 K. The measured flux noise above 10 kHz at 4 K is $80\;\mathrm{n}\Phi_0 \mathrm{Hz}^{-1/2}$ at a bandwidth of 200 MHz. Estimations suggest that one can benefit from parametric gain based on inherent nonlinearity of the Josephson junction and reduce the flux noise to $30\;\mathrm{n}\Phi_0\mathrm{Hz}^{-1/2}$ at 100 mK, which corresponds to $7.5\;\mathrm{\mu_B Hz^{-1/2}}$ for a magnetic moment located at the center of the pickup loop.