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- SQUID Amplifiers for Axion Search Experiments
SQUID Amplifiers for Axion Search Experiments
in: Cryogenics (2018)
In the experiments for dark-matter QCD-axion searches very weak microwave signals from a low-temperature high-Q resonant cavity should be detected with the highest sensitivity. The best commercial low-noise cryogenic semiconductor amplifiers based on high electron mobility transistors (HEMT) have the lowest noise temperature above 1 K, even if they are cooled well below 1 K. Superconducting quantum interference devices (SQUIDs) can work as amplifiers with temperature noise close to the quantum limit. First SQUID-based RF amplifiers designed for axion search experiments have a microstrip resonant input coil and are thus called micro-strip SQUID amplifiers or MSAs. Due to the resonant input coupling they have narrow bandwidth 10 – 100 MHz. The resonance frequency can be tuned by connecting an external varactor circuit. Recently a new SQUID-based wideband microwave amplifier fabricated at the Leibniz Institute of Photonic Technology (Leibniz-IPHT, Jena) was first time tested at the Center for Axion and Precision Physics (IBS/CAPP, Daejeon). It has gain more than 15 dB in frequency range from 1.0 to 2.3 GHz and more than 10 dB in frequency range from 3.8 to 5.0 GHz.