Quantum Systems

The sensor, called herein GHS, is based on a dc SQUID connected to a SQIF that amplifies the voltage from the first stage SQUID. The SQIF consists of an array of SQUIDs with various inductances, facilitating a unique global minimum in the flux-voltage-characteristic and ensures a stable working point, a high voltage swing and a large transfer function of the GHS. Sub-micrometer cross-type Josephson junctions are used for the GHS. Due to their low capacitance, the sensors exhibit low magnetic flux noise and a high voltage swing. The voltage swing of the SQIF can exceed 3 mV which enables the use of a high-bandwidth directly coupled SQUID electronics. A part of the current of the SQIF can optionally be fed back to the input coil of the first stage SQUID, so that an on-chip linearization is realised. The used sub-micron cross-type junctions withstand high background fields during cool-down of up to 6.5 mT. The high voltage swing as well as the optional on-chip linearization make this setup well suited for applications in strong magnetic fields where high slew rates are required, like e.g. the transient electromagnetic method.