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 ICRN-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 45nΦ0/Hz1/2 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.
@article{arxiv.1705.06166,
title = {Nearly quantum limited nanoSQUIDs based on cross-type Nb/AlOx/Nb junctions},
author = {M. Schmelz and V. Zakosarenko and T. Schönau and S. Anders and S. Linzen and R. Stolz and H. -G. Meyer},
journal= {arXiv preprint arXiv:1705.06166},
year = {2017}
}