Nearly quantum limited nanoSQUIDs based on cross-type Nb/AlOx/Nb junctions

TL;DR

This paper presents the development of nearly quantum limited nanoSQUIDs using high-quality Nb/AlOx/Nb Josephson junctions, achieving extremely low flux noise and high sensitivity suitable for advanced sensing applications.

Contribution

Introduction of nearly quantum limited nanoSQUIDs with miniature loops and high-quality junctions, enabling ultra-low noise and high sensitivity in magnetic sensing.

Findings

Flux noise as low as 45 nΦ₀/Hz^{1/2} at 4.2 K

Energy resolution of about 1 h at 4.2 K

Large voltage swings (~300 μV) for sensitive operation

Abstract

We report on the development of nearly quantum limited SQUIDs with miniature pickup loop dimensions. The implemented high quality and low capacitance cross-type Nb/AlOx/Nb Josephson junctions offer large $I_CR_N$-products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 {\mu}m exhibit white flux noise levels as low as $45 n{\Phi}_0/Hz^{1/2}$ corresponding to an energy resolution {\epsilon} of about 1 h at 4.2 K, with h being Plancks constant. Moreover, the large usable voltage swings of the devices of about 300 {\mu}V allow highly sensitive and easy single-stage operation while exploring nearly the intrinsic noise of the SQUIDs, beneficial e.g. for sensor arrays in SQUID microscopy.