Advances in SQUID-Based Detectors and Measurement Devices

Dear Colleagues,

Almost 60 years after the development of superconducting quantum interference devices, so-called SQUIDs, they are still a key enabling element of superconducting and quantum electronics driving recent research. Using quantum effects, they have unique properties such as high sensitivity, ultra-low noise and wide bandwidth and thus enable a large number of applications. In order to adapt them to different requirements, several versions of SQUIDs have developed such as basic RF and DC SQUIDs, Bi-SQUIDs, unSQUIDs, nanoSQUIDs and arrays thereof. As single analogue SQUID detectors deliver a small amplitude output signal in conjunction with nonlinear characteristics, they are usually driven by dedicated read-out electronics. These often use feedback loop schemes providing a linear output at increased dynamic range and ultra-low noise. Variants with direct coupling, modulation schemes, or even ac-bias versions have been implemented. Furthermore, digital SQUIDs have been developed to increase the dynamic range further.

Any physical property can be measured by a SQUID when transferrable into magnetic flux coupled to the SQUID. For direct detection of macroscopically distant magnetized sources, the magnetic field is transduced into flux in the SQUID itself and should be detected with high resolution. The transduction factor can be maximized with specific SQUID designs using flux focusing or direct injection, flux transformers or fractional loops. Further improvements are possible by external flux focusing arrangements of highly permeable materials.

The SQUID performance depends strongly on the Josephson junction’s quality, materials and fabrication technologies. These technologies are as diverse as the available Josephson junction technologies.

In recent decades, a large number of applications were addressed with SQUIDs in magnetometry for biomagnetism, non-destructive evaluation, and geophysics, in the sensing of currents, voltages, and temperatures, and in radiation detection as well as in amplification, multiplexing and readout of other sensors and circuits. Accordingly, this Special Issue seeks to highlight research papers, short communications, and review articles that focus on novel methodological developments in SQUID-based devices in related applications.

We welcome you to contribute to this Special Issue!

Dr. Denis Gérard Crété
Dr. Ronny Stolz
Guest Editors

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• superconductivity
• quantum device
• SQUID
• SQUID arrays
• SQIFs
• SQUID readout
• fabrication technologies
• SQUID applications
• magnetometry
• flux
• detection
• measurement
• low frequency
• radiofrequency
• sensitivity
• noise