Aalto unveils first superconducting quantum heat engine

Researchers at Aalto University have demonstrated the world's first cyclic quantum heat engine built inside a superconducting circuit, according to a study published in Nature Communications on August 14, 2026. The device, which operates near absolute zero, repeatedly produced positive work by converting tiny amounts of heat, marking a proof of concept for superconducting heat engines that could eventually improve quantum computing technology.

The engine combines a transmon qubit, a resonator, and a quantum refrigerator, all nanofabricated within a superconducting circuit. Led by Academy Professor Mikko Möttönen, the team used the quantum refrigerator to both heat and cool the qubit on demand, driving an Otto cycle—the same thermodynamic process used in car engines—through carefully timed control pulses. Measurements confirmed that heat passing through the qubit during the cycle generated positive work.

This experiment bridges quantum mechanics and thermodynamics, showing how familiar thermodynamic processes behave when quantum effects such as tunneling, entanglement, and superposition are present. According to first author Tuomas Uusnäkki, the use of a single controllable quantum refrigerator as both the hot and cold environment makes the system simpler and more versatile than conventional heat engines, which rely on separate hot and cold reservoirs.

The researchers are now working to improve the design and develop a fully autonomous heat engine. One potential application is reading out qubits without carrying microwave pulses from millikelvin temperatures to room temperature. Möttönen notes that Finland's Quantum Technology Strategy envisions a quantum computer with one thousand logical qubits by 2035, which would likely require hundreds of thousands of physical qubits and millions of microwave cables costing thousands of euros each. Autonomous devices integrated into superconducting circuits could reduce both cost and complexity while eliminating much of the noise introduced by cables.

The experiment was carried out using OtaNano, Finland's national research infrastructure for nano, micro, and quantum technology. Funding came from the Research Council of Finland and the Finnish Cultural Foundation.