Researchers at Aalto University have demonstrated the world's first cyclic quantum heat engine built inside a superconducting circuit — a nanofabricated device that converts heat near absolute zero into measurable, positive work, cycle after cycle. The study, led by Academy Professor Mikko Möttönen and published in Nature Communications on August 14, 2026, is a proof of concept for hardware that could eventually simplify quantum computers with hundreds of thousands of qubits.

The engine is small in every sense. It combines a transmon qubit, a resonator and a quantum circuit refrigerator, all operating inside a cryostat at millikelvin temperatures. Yet the physics it demonstrates is anything but small, touching the border between quantum mechanics and thermodynamics.

"In our experiment, we built a nanofabricated heat engine using superconducting circuits and operated it in a cryostat near absolute zero. At its heart is a transmon qubit, one of the basic building blocks of modern quantum technologies," says Tuomas Uusnäkki, the study's first author.

What did the engine actually do?

The team reproduced an Otto cycle — the same thermodynamic process that drives car engines — inside the superconducting circuit. In a conventional heat engine, heat flows between a hot environment and a cold one, and the machine converts part of that flow into useful work. James Watt's steam engine set the template; modern power plants still follow it.

Here, the roles get strange. Instead of separate hot and cold reservoirs, a single quantum circuit refrigerator supplies both, tunable on demand.

"Our quantum-circuit refrigerator can be tuned to both heat and cool the qubit on demand. Using carefully timed control pulses, we drove the engine in an Otto cycle and monitored the qubit state as the engine ran," Uusnäkki explains.

Measurements confirmed that heat passing through the qubit during the cycle produced positive work — repeatedly. That cyclic operation is what researchers in the field have chased for years, and Aalto's device is the first to achieve it in superconducting hardware.

"This is the first experimental demonstration of a cyclic quantum heat engine in superconducting circuits. Using a single controllable quantum refrigerator as both the hot and cold environment of the engine makes it simpler and more versatile," says Uusnäkki.

Why does this matter for scaling quantum computers?

The commercial stakes lie in cabling. Today, reading out a qubit requires carrying a microwave pulse from millikelvin temperatures all the way up to room-temperature electronics. That works fine for a few dozen qubits. It breaks down badly at scale.

Möttönen puts numbers on the problem. Finland's Quantum Technology Strategy targets a quantum computer with one thousand logical qubits by 2035 — which, he notes, probably means hundreds of thousands of physical qubits. Current qubit architectures encode each logical qubit across many physical ones, so the multiplier is brutal.

"Doing that with current technology requires millions of microwave cables costing thousand euros each. The cables also introduce noise into the system. Using autonomous devices instead would mostly eliminate the need for those cables," Möttönen says.

Do the arithmetic and the cable bill alone reaches into the billions of euros. The noise those cables inject into the system compounds the cost problem, degrading the very qubits they're meant to serve.

A fully autonomous heat engine integrated directly into superconducting circuits could address both problems at once — one possible use is qubit readout that never needs a signal carried out of the cryostat.

What comes next?

The current device is a demonstration, not a product. The researchers are now working to improve the design and move toward a fully autonomous heat engine, one that runs without external control pulses timing every stroke of the cycle.

The experiment ran on OtaNano, Finland's national research infrastructure for nano, micro and quantum technology, with funding from the Research Council of Finland and the Finnish Cultural Foundation. The paper, "Initial demonstration of a quantum heat engine based on dissipation-engineered superconducting circuits," appears in Nature Communications, volume 17.

If the team can push from cyclic demonstration to autonomous operation, superconducting quantum processors could shed the densest, noisiest and most expensive part of their wiring harness — and the path from hundreds of qubits to hundreds of thousands gets measurably cheaper.