Design and Modeling of Superconducting Quantum Amplifiers for Fundamental Physics Experiments
Tian Bai, Tom Godfrey, Parth Bhandari +5 more
The Superconducting Low-inductance Undulatory Galvanometer (SLUG) is a linear, phase-sensitive, quantumlimited amplifier that can amplify ultra-weak microwave signals at frequencies up to 10 GHz or potentially higher, such as the output from cavity-based searches for the axion, a dark matter candidate. The SLUG amplifier differs from the closely related Superconducting Quantum Interference Device (SQUID) amplifier in that the input signal is directly injected into the SLUG rather than being inductively coupled through a multiturn input coil. The direct injection greatly simplifies the SLUG's microwave circuit integration and modelling, whilst enabling potentially higher frequency operation. Here we present the design and modelling of a SLUG amplifier that can be realised from a single-layer of Nb, with nanobridge weak-links fabricated using either electron-beam (EBL) or focussed ion beam (FIB) lithography as the Josephson elements. We discuss the input and output impedance, the forward transimpedance, and the potential power gain assuming a matched source and load. We also discuss the necessary impedance matching of the SLUG to the characteristic 50 Ω on-chip microwave environment.
IEEE Transactions on Applied Superconductivity•Mar 30, 2026•0 citations