As superconductor circuits gets faster and more complex, the CAD tools becomes the bottleneck of what these circuits could achieve. Advances in fabrication and circuit design needs more advanced analyze tools. Open-source design and simulation programs play a crucial role in this matter since they are used by more users. More users means that we find out about the limits and shortcomings of the tools faster, more developers will contribute to advancing the tool and it makes the field approachable for new researchers and enthusiasts.
Some projects have been launched for developing design tools. The most notable of these projects are ColdFlux/ Supertools [1] project. The goal of this project is designing new open-source software that encompass all the aspects of a circuit design from basic physics to more advance digital optimizations. Fig. 1 shows the different tools developed in duration of the ColdFlux project.
There are different levels to design a circuit. The user needs to extract the characteristics of each basic circuit element such as Josephson junctions and inductances based on the fabrication process, design a schematic for the sub-circuit and optimize it, design a layout for that sub-circuit and extract the parasitic elements from layout and back annotate it to schematic and finally optimize the whole sub-circuit. More complex circuits are formed from these sub-circuits. The complex circuits are designed and optimized on a system level with digital tools such as customized Verilog or VHDL.
We have designed a software named JOINUS[2], in scope of ColdFlux project. JOINUS is a user friendly, open-source interface that encompass all the developed programs and help the user to characteristic a simple Josephson junction to simulate and optimize a full chip. The final goal of JOINUS is to automize most of the design process so even a relatively unexperienced user can design a full chip.

References
[1] C. J. Fourie, K. Jackman, M. M. Botha, S. Razmkhah, P. Febvre, C. L. Ayala, Q. Xu, N. Yoshikawa, E. Patrick, M. Law, Y. Wang, M. Annavaram, P. Beerel, S. Gupta, S. Nazarian, and M. Pedram, ColdFlux Superconducting EDA and TCAD Tools Project: Overview and Progress, IEEE Transactions on Applied Superconductivity 29, 1 (2019).
[2] S. Razmkhah and P. Febvre, JOINUS: A User-Friendly Open-Source Software to Simulate Digital Superconductor Circuits, IEEE Transactions on Applied Superconductivity 30, 1 (2020).

Keywords: Open-Source Software, Superconducting electronics, Single Flux Quantum, Josephson Simulator