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

R N Jabdaraghi,D S Golubev,J T Peltonen,J P Pekola

doi:10.1038/s41598-017-08710-7

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 ~4 μΦ0/Hz1/2, 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.

Highlights

Measuring noise provides an uncompromising test of microscopic and nanoscopic superconducting sensors[1,2,3,4,5], such as superconducting quantum interference devices (SQUIDs), for ultra-sensitive detection of weak and local magnetic signals
We show that the low-temperature readout of RLC filtered shot noise can be applied to the study of nonlinear devices once changes in the differential resistance are taken into account, cf. gate-tunable semiconducting devices where the resistance depends only weakly on the bias voltage
A typical SQUIPT based on a superconducting aluminium loop placed into a perpendicular magnetic field is presented in Fig. 1(a), with an enlarged view of the weak link region depicted in the top inset

Summary

Introduction

Measuring noise provides an uncompromising test of microscopic and nanoscopic superconducting sensors[1,2,3,4,5], such as superconducting quantum interference devices (SQUIDs), for ultra-sensitive detection of weak and local magnetic signals. The shot noise[21, 22] in the electrical current of a biased conductor provides information on quantum transport in mesoscopic structures beyond the average current[23] It has been measured in various systems, including quantum point contacts (QPCs)[24, 25] and quantum dots (QDs)[26], and found to provide an accurate means of primary thermometry for metallic tunnel junctions[27, 28] and recently for QPCs as well[29]. A successful technique for measuring the shot noise of high-impedance semiconducting samples relies on a cryogenic amplifier based on a high electron mobility transistor (HEMT) and an RLC tank circuit with resonance frequency of a few MHz14–16. We show that the low-temperature readout of RLC filtered shot noise can be applied to the study of nonlinear devices once changes in the differential resistance are taken into account, cf. gate-tunable semiconducting devices where the resistance depends only weakly on the bias voltage

Methods

Results

Conclusion