Quantum Systems

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 allow for the measured exceptional low noise level of the SQUIDs. Devices with loop dimensions of 1 µm exhibit white flux noise levels as low as 45 n0/Hz1/2 corresponding to an energy resolution  of about 1 h at 4.2 K, with h being Planck’s constant. The large usable voltage swings of the devices of about 300 µV moreover offer 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.