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

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 $I_C{R}_N$-products and therefore enable an exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 μm exhibit white flux noise levels as low as $45n{\Phi }_0/H{z}^{1/2}$ corresponding to an energy resolution ε 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 μV 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.

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• Quantum thermodynamic derivation of the energy resolution limit in magnetometry
• Superelliptic Josephson Tunnel Junctions