Low-frequency circuits with superconducting inductance.

Gemma Chapman, Tom Godfrey, Jamie Potter +5 more

The Superconducting Low-inductance Undulatory Galvanometer (SLUG) amplifier is an ultra-low noise rf amplifier that is simple to operate and can be designed for a wide range of microwave frequencies. A variant of the dc SQUID rf amplifier, the SLUG differs in that the rf signal is directly injected in the SQUID loop, allowing high frequency operation. Here, we realize a planar SLUG amplifier constructed with nanobridge weak-link junctions that is fabricated from a single layer of niobium. Impedance models for the SLUG gain element are presented in conjunction with a discussion of appropriate impedance matching techniques. Experimental characterization of a proof-of-concept SLUG amplifier designed with a single-stub tuning circuit show modulation of the SLUG operation frequency in line with biasing of the SLUG, a well-matched input network and forward gain of 8 dB.

Pascal Febvre

C.J. Fourie, Romain Collot, Pascal Febvre +4 more

John C. Gallop

Guilhem J. Ribeill, David J. Hover, Yung‐Fu Chen +2 more

We describe a novel scheme for low-noise phase-insensitive linear amplification at microwave frequencies based on the superconducting low-inductance undulatory galvanometer (SLUG). Direct integration of the junction equations of motion provides access to the full scattering matrix of the SLUG. We discuss the optimization of SLUG amplifiers and calculate amplifier gain and noise temperature in both the thermal and quantum regimes. Loading of the SLUG element by the finite input admittance is taken into account, and strategies for decoupling the SLUG from the higher-order modes of the input circuit are discussed. The microwave SLUG amplifier is expected to achieve noise performance approaching the standard quantum limit in the frequency range from 5–10 GHz, with gain around 15 dB for a single-stage device and instantaneous bandwidths of order 1 GHz.

Guilhem J. Ribeill, David J. Hover, Y. F. Chen +2 more

We describe a novel scheme for low-noise phase-insensitive linear amplification at microwave frequencies based on the Superconducting Low-inductance Undulatory Galvanometer (SLUG). Direct integration of the junction equations of motion provides access to the full scattering matrix of the SLUG. We discuss the optimization of SLUG amplifiers and calculate amplifier gain and noise temperature in both the thermal and quantum regimes. Loading of the SLUG element by the finite input admittance is taken into account, and strategies for decoupling the SLUG from the higher-order modes of the input circuit are discussed. The microwave SLUG amplifier is expected to achieve noise performance approaching the standard quantum limit in the frequency range from 5-10 GHz, with gain around 15 dB for a single-stage device and instantaneous bandwidths of order 1 GHz.