Cryogenic detectors are an emerging key technology for applications in science, society and industry. Ultra-high resolution, universal use for matter and radiation, linearity and high quantum efficiency are very attractive features of such devices for particle detection, metrology, radiation spectroscopy and mass spectrometry. Several universities and research institutes have now joint forces to develop and establish cryogenic detectors and the associated superconducting electronics, as well as developing detectors systems and necessary cryo-technology for future research and applications.

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Cryogenic Detectors

Magnetic Micro-Calorimeters

MMCs: The extremely high resolving power of magnetic micro-calorimeters and their linearity and speed make them unique tools in a wide range of precision measurements. Their principle of operation is based on the change of the magnetisation of paramagnetic metals. State of the art MMCs have shown excellent resolving powers, signal rise times of better that 100 ns and non-linearites of better than 1%. Their promising potential has already been demonstrated in numerous fields ranging from neutrino physics to X-ray spectroscopy and nuclear forensics.

Transition-Edge Sensors

TES: Operating at the sharp transition between the superconducting and normal state of metals, this type of mirco calorimeter translates small temperature changes into large signals that allow relatively easy amplification and multiplexing. In negative electrothermal feedback mode, it is self-stabilizing and has proven extremely high resolving powers. These excellent properties already make them the technology of choice in many applications, from THz spectroscopy to CMB measurements to gamma spectroscopy.

Superconducting Electronics

SQUIDs

Superconducting Quantum Interference Devices based on Josephson tunnel junctions allow to measure any kind of physical quantity that can be naturally converted into a change of magnetic flux with extremely high precision. Dc-SQUIDs routinely achieve a noise performance close to the quantum limit. In combination with their intrinsic compatibility with sub-K operation temperature, they are hence ideally suited for reading out cryogenic detectors like MMCs and TESs. Beyond cryogenic detectors SQUIDs have an extremely broad range of applications from the measurement of biomagnetic signals to archaeology and the search for important commodities.

Microwave-SQUID Multiplexing

Frequency-division multiplexing in the GHz range is the most promissing scheme for the readout of large-scale multi-pixel cryogenic detectors arrays based on TESs or MMCs. This type of readout is based on modulating the signals of individual detectors onto microwave carrier frequencies by means of non-hysteretic rf-SQUIDs and microwave resonators. Encoding and decoding the signals of individual detectors are performed by a dedicated software defined radio system. This type of multiplexing is not only applicable for reading out cryogenic detectors, but has also already shown its enormous advantages for addressing and reading out superconducting qubits.