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History

  • The JOINUS (JOsephson INterface Utility Software) project1 was started in 2017 through an initial support by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA) as part of the ColdFlux/SuperTools project. The objective was to develop and make accessible to the broader community practical tools for simulating quantum superconducting electronics circuits. In this regard, JOINUS incorporates SPICE-based simulator engines, enhanced physical models, and several powerful built-in routines. JOINUS is based on a user-friendly environment available on Linux, MacOS, and Windows platforms, which simplifies the design and analysis of superconducting digital circuits.

  • However, the design of circuits remained largely manual because there were no convenient and compatible free-source tools available for drawing schematics of superconducting circuits. To address this gap, L2SPICE (LibrePCB to SPICE netlist converter) was born at the University of Savoie Mont Blanc in France and developed from 2023 until early 2024. L2SPICE converts schematics drawn by LibrePCB into SPICE netlists used by JOINUS-D.

  • Since 2025 JOINUS-D (formerly JOINUS) and L2SPICE are embedded in the open source FrugalEDA project for Education and Research purposes developed by the French SEFIRA Society. It is funded through the NGI0 Core Fund, a fund established by NLnet with financial support from the European Commission's Next Generation Internet programme, under the aegis of DG Communications Networks, Content and Technology under grant agreement No 101092990.

  • FrugalEDA currently embeds the following set of tools to design quantum superconducting electronics circuits:

    • LibrePCB, a "free, cross-platform, easy-to-use electronic design automation suite to draw schematics and design printed circuit boards – for makers, students and professionals, from beginners to experts."
    • SuperLibre: A comprehensive library of superconducting components, designed to facilitate the creation of schematics for quantum superconducting electronics circuits using LibrePCB.
    • L2SPICE is a tool that converts LibrePCB schematics into SPICE netlists compatible with JOINUS. It also allows for back-annotating schematics during the design and optimization process.
    • JOINUS-D (Josephson Interface Utility Software for Digital Superconducting Circuit Simulations) is the primary software used for designing, simulating, analyzing, and optimizing superconducting circuits, as well as displaying the results. JOINUS-D leverages L2SPICE as its underlying technology to facilitate the conversion of netlists between LibrePCB and SPICE formats.
    • JSIM (Josephson Junction aware SPICE simulator) is an analog circuit simulator specifically designed for superconducting electronics and Josephson-junction-based circuits. It provides SPICE-based transient simulations of superconducting circuits and has been widely used for Single-Flux-Quantum (SFQ) circuit design and analysis.
    • JoSIM (Josephson Simulator) is a modern SPICE-compatible analog circuit simulator specifically designed for superconducting circuits. It supports superconducting elements such as Josephson junctions, implements the RCSJ model, and performs transient simulations while providing simulation results in standard data formats.
    • FrugalPlot serves as an interactive graphical tool that enables users to visualize results on graphs and input digital criteria using the mouse, thereby feeding JOINUS-D algorithms.
    • QtGrace is a Qt-based scientific plotting and data-analysis tool derived from Grace. It allows users to import numerical data, create and edit two-dimensional graphs, perform analyses such as curve fitting and FFT, and export publication-quality plots.
    Note

    LibrePCB, JSIM, JoSIM, and QtGrace are external tools integrated into FrugalEDA to facilitate and streamline the circuit design workflow.

Copyright (C) 2025-2026 FrugalEDA developers.

FrugalEDA is open source software. For the latest updates and source code, visit our repository.

  1. S. Razmkhah and P. Febvre, "JOINUS: A User-Friendly Open-Source Software to Simulate Digital Superconductor Circuits," IEEE Transactions on Applied Superconductivity, vol. 30, no. 5, pp. 1-7, Aug. 2020, Art no. 1300807. [https://doi.org/10.1109/TASC.2020.2976600 – https://doi.org/10.48550/arXiv.1909.12421 ↩