I designed such superconducting chips for my MSc thesis and had them manufactured by Hypres, one of the few foundries that offered such a process. Designing sup

I designed such superconducting chips for my MSc thesis and had them manufactured by Hypres, one of the few foundries that offered such a process. Designing superconducting circuits is great fun, I even wrote my own circuit simulator (https://github.com/adewes/superconductor/ https://github.com/adewes/superconductor/). RSFQ (Rapid Single Flux Quantum Logic, or as some would jokingly say Russian Single Flux Quantum Logic) was quite hyped up in the nineties, Prof. Likharev at Stony Brook had a collaboration with IBM working on RSFQ circuit elements to replace conventional semiconductor logic. At the time the achievable speed was fantastic as compared to regular circuits, (un)fortunately semiconductor processes kept evolving and today RSFQ is only interesting for some niche applications like fast microwave circuits at cryogenic temperatures (and even there HEMT transistors are often a better solution nowadays). Also, getting circuits with more than 10.000 junctions to work was quite tricky as the fabrication processes weren't very reliable and transferring flux quanta is a bit more noisy than storing charges on an FET, so I'm doubtful whether we could even have large-scale RSFQ circuits without extensive error correction. Well, it's still an amazingly fun and fascinating field, really hope we might see a revival of it one day (maybe if we get room-temperature superconductors).