Despite all the glamorous promises made about quantum computing, it’s hard to make the argument that today’s quantum computers hold a candle to the sheer practicality of classical computers, especially when qubits need to be cuddled at cryogenic temperatures inside a cryostat. This is worsened by the problem that regular semiconductor transistors do not really appreciate these same cryogenic temperatures, creating an awkward interfacing problem for the controlling electronics.
Now a new pitch here is to create superconducting transistors that will happily work at temperatures near absolute zero. In an article in IEEE Spectrum this start-up – called S-Transistors – and their concept are covered.
By being able to have the control circuits inside the same cryostat, one can forego the absolute mess of wiring that has to penetrate it, and with it one major failure point. Their proposed solution uses the same Josephson junctions (JJs) that are also used for qubits, using a high enough current to briefly make it non-superconducting, inducing a voltage pulse that can be detected.
In addition, JJ-based field effect transistors (JJFETs) are used, with this 2025 paper by [Yusheng Xiong] et al. detailing these structures. Here S–Transistors claims that they are now able to manufacture JJFETs at scale, which would be another major breakthrough that could bring quantum computing just a little bit closer.
They’d be competing with cryogenic CMOS (Cry-CMOS), which can use standard semiconductor production lines to create circuits that can withstand cryogenic temperatures, albeit not quite a the near-zero K level that these superconducting transistors and JJFETs would be capable of.
After many months of painstaking work, [AlfMart CNC Garage] over at YouTube has finally reached the stage where he can 
