A startup called S-Transistors is building superconducting transistors designed to operate near absolute zero, with the goal of placing control electronics inside the same cryostat as the qubits. The core problem they are solving: standard semiconductor transistors fail at cryogenic temperatures, forcing engineers to route a tangle of wiring through the cryostat wall, a major interference and failure point.
Their approach uses Josephson junctions, the same structures already used to build qubits, driven with enough current to briefly break superconductivity and produce a detectable voltage pulse. They are also manufacturing Josephson junction field effect transistors, or JJFETs, at scale, a claim backed by a 2025 paper by Yusheng Xiong et al. on arXiv. The IEEE Spectrum article is worth reading for how S-Transistors positions JJFETs against cryogenic CMOS, the competing approach that uses standard semiconductor fabs to produce circuits tolerant of cold, but not near-0 K cold.
The manufacturing-at-scale claim is the number to interrogate. Cryogenic CMOS has a production line advantage that superconducting transistors do not yet match. Whether JJFETs can close that gap determines whether this is a real integration path for quantum control electronics or another promising physics demo.
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