Wave Propagation through a Jasephson-Junction Transmission Line

Ryogo Hirota

A. Barone, R.D. Permentier

Michael Haider, Yongjie Yuan, Christian Jirauschek

A major challenge for the experimental realization of advanced superconducting traveling-wave parametric amplifiers is given by proper impedance matching of the input and output transmission lines and the active region with periodically embedded Josephson junction arrays. For a large impedance mismatch, non-negligible reflections occur at the interfaces, leading to a co-propagation of cavity-like modes. In this contribution, we want to assess the effects of improper impedance matching on the transmission spectrum of traveling-wave parametric amplifiers using a simple overlay cavity model. Our results can serve as a guideline for design limitations of Josephson-junction-embedded transmission lines.

Susanne Lomatch, E. D. Rippert

We present a new type of Josephson transmission line (JTL) in which discrete multilayer Josephson junctions are employed instead of the standard single tri-layer junction technology. It is shown via numerical simulation that such a structure supports the propagation of multiple flux quantum solitons, which are represented in this system by a 2πn kink in the phase difference across a multilayer junction of n superconductor-insulator-superconductor layers. As a practical aspect, parallel and series connected multilayer junctions in a JTL can significantly reduce the need for microstrip line inductance, thereby providing the optimal conditions for large scale integration of JTL-based logic and memory circuitry. In this article we investigate in detail through numerical simulation the properties of JTL designs with multilayer junctions, incorporating expected variations in junction characteristics. A brief description of the current fabrication of multilayer junctions for flux quantum circuitry will be provided.

Richard J. Collier