S-Transistors raises €2.6M to move quantum controls inside the cryostat

Why it matters

Quantum processors can add qubits faster than cryogenic control systems can add cables and cooling capacity. S-Transistors is betting a new transistor can become that missing control layer.

Heorhii Bohuslavskyi and Andrey Generalov have raised €2.6 million for S-Transistors, the VTT spinout they founded to build control electronics that can operate beside a quantum processor at millikelvin temperatures. S-Transistors announced the pre-seed round on August 31, with Lifeline Ventures leading and an unnamed angel investor participating.

Bohuslavskyi, S-Transistors' CEO, has spent his career working on the awkward interface between quantum devices and conventional electronics. He earned a PhD in nanophysics from Grenoble Alpes University in 2018, studying cryogenic electronics and silicon quantum dots, and later conducted research at NTT in Japan before joining VTT. His work has covered cryogenic CMOS, qubit control, quantum sensing and neuromorphic hardware.

Generalov, S-Transistors' CTO, brings the manufacturing side of the bet. He completed a doctorate at Aalto University in 2015 on sub-terahertz waveguide components, and VTT credits him with 15 years of work spanning microfabrication, wafer-scale process development, graphene transistors and superconducting integrated circuits.

The pair are trying to commercialize a device that has largely remained a research subject: a transistor whose switching behavior can be controlled electrically while carrying current through a superconducting channel. Their intended payoff is a classical control layer that can sit in the same extreme cold as superconducting qubits without overwhelming the refrigerator's limited cooling capacity.

The cable problem becomes a chip problem

Superconducting quantum processors are kept inside dilution refrigerators, while much of their control and readout equipment remains at room temperature. Signals travel between the two through cables entering the cryostat. Adding qubits therefore means adding wiring, connectors and heat loads alongside the control hardware itself.

Bohuslavskyi calls that architecture a "hard wall" for scaling. S-Transistors' proposed fix is to move more switching, signal routing and interface electronics into the cryostat, close to the quantum processing unit. Conventional silicon transistors can operate at cryogenic temperatures, but power consumption and heat dissipation become increasingly restrictive as control systems grow.

S-Transistors is building its integrated circuits around graphene Josephson field-effect transistors. Generalov and Bohuslavskyi were among the authors of a 2024 Applied Physics Letters paper reporting wafer-scale, CMOS-compatible fabrication of these devices. The researchers demonstrated repeatable electrical control of the devices' critical current across multiple gate lengths.

That paper establishes a fabrication process and tunable devices, rather than a finished quantum-control system. S-Transistors still has to show that its circuits can deliver useful speed, yield, reliability and power performance when connected to operating quantum hardware. The announcement provides no independent system-level benchmarks against cryogenic CMOS or single-flux-quantum control electronics.

The €2.6 million round is structured around producing that evidence. S-Transistors plans to establish a cryogenic laboratory, build signal-control prototypes, create a pilot manufacturing line and add staff. Lifeline Ventures partner Jyri Engestrom is backing a familiar deep-tech progression: move a device from a research wafer into a repeatable circuit, then prove that customers can integrate it.

S-Transistors disclosed the round size, while the valuation, ownership terms and identity of the angel investor remain outside the announcement.

A multiplexer comes before the motherboard

S-Transistors' first planned product is a superconducting-transistor multiplexer for routing signals inside existing cryogenic setups. S-Transistors says it will ship the device to early customers and strategic partners within its first year of operation.

The multiplexer gives Bohuslavskyi and Generalov a narrower engineering and commercial target than their longer-term "quantum motherboard" concept. Researchers and hardware developers can test a signal-routing component without redesigning an entire quantum computer around S-Transistors' architecture. Successful deployments would also generate the operating data needed to judge whether the underlying transistor platform can support denser control circuitry.

The eventual motherboard is meant to combine signal routing, control and interfaces around the quantum processor at millikelvin temperatures. Reaching that point will require integrated circuits far more complex than the devices described in the founders' 2024 paper. It will also depend on compatibility with the packaging, wiring and qubit designs used by quantum-computer manufacturers.

S-Transistors is entering a field where several architectures are already competing to pull control hardware closer to the qubits. Fellow VTT spinout SemiQon is developing cryogenic CMOS transistors designed for operation at 1 kelvin and below. SEEQC uses superconducting single-flux-quantum logic and says its digital control circuits can operate at the same 20 millikelvin stage as superconducting qubits.

Bohuslavskyi and Generalov are making a different device-level wager: transistor-style electrical control combined with superconducting operation and a wafer-scale graphene process. That could provide a useful middle ground between familiar transistor circuits and fully superconducting digital logic, provided S-Transistors can manufacture the devices consistently and integrate enough of them into practical circuits.

For the founders, the round marks the point where years of cryogenic-electronics research acquire a product deadline. The first multiplexer will determine whether S-Transistors has a component customers can use. The manufacturing pilot will determine whether the founders have the beginnings of a semiconductor business rather than another promising low-temperature experiment.