Scientists have built a tiny superconducting heat engine. It turns quantum-scale heat into useful work. This could make large quantum computers much easier to build.
This new engine helps us understand how thermodynamics works in the quantum world. This knowledge can benefit quantum technology and our understanding of basic thermodynamic rules. Researchers at Aalto University created the first cyclic quantum heat engine inside a superconducting circuit.
The experiment connects two different areas of physics. Quantum mechanics explains things smaller than atoms. Thermodynamics describes how heat and energy work in much larger systems. Bringing them together helps answer what happens to heat processes when quantum effects like tunneling and entanglement are involved.
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Start Your News DetoxA Heat Engine for the Quantum World
Regular heat engines turn heat into useful work. Think of a car engine or a power plant. The new device is the world's first superconducting quantum heat engine. It is very small and combines a transmon qubit, a resonator, and a quantum refrigerator.
The engine works in extremely cold quantum conditions. It uses tiny amounts of heat to repeatedly produce positive work. This cyclic operation was a key goal for quantum heat engine researchers. This shows that superconducting heat engines are possible. They could improve quantum computing technology.
Academy Professor Mikko Möttönen led the study. It was published in Nature Communications.
Recreating an Otto Cycle Near Absolute Zero
The researchers made the engine work by using an Otto cycle. This is a thermodynamic process also found in car engines.
Tuomas Uusnäkki, the study's first author, explained their work. They built a tiny heat engine using superconducting circuits. They ran it in a cryostat, a super-cold environment, near absolute zero. The core of the engine is a transmon qubit, a basic part of quantum technology.
The transmon qubit was connected to a quantum circuit refrigerator. This allowed them to control heat flow at the quantum level. They showed that this heat could be turned into measurable work. A normal heat engine needs separate hot and cold areas. But this system uses the same quantum refrigerator for both heating and cooling.
Uusnäkki noted that their quantum-circuit refrigerator can heat and cool the qubit as needed. They used timed control pulses to run the engine in an Otto cycle. They watched the qubit's state as it ran.
Measurements showed that heat moving through the qubit during the cycle created positive work. Uusnäkki said this is the first time a cyclic quantum heat engine has been shown in superconducting circuits. Using one controllable quantum refrigerator for both hot and cold parts makes it simpler.
Towards Autonomous Quantum Computers
The researchers are now working to improve the design. They want to create a fully autonomous heat engine. One use could be reading qubits without sending microwave pulses from super-cold temperatures to room temperature.
This would be very helpful as quantum computers get bigger. Autonomous devices built directly into superconducting circuits could lower the cost and complexity of machines with many qubits.
Möttönen mentioned Finland's Quantum Technology Strategy. It aims for a quantum computer with one thousand logical qubits by 2035. This would mean hundreds of thousands of physical qubits. Current technology would need millions of microwave cables, each costing thousands of euros. These cables also add noise to the system. Using autonomous devices would mostly remove the need for these cables.
Reducing these microwave connections would solve two problems. It would address the huge hardware needs of large quantum computers. It would also reduce the unwanted noise that cables can bring into quantum systems.
The experiment used OtaNano, Finland's national research facility for nano, micro, and quantum technology. Funding came from the Research Council of Finland and the Finnish Cultural Foundation.
Deep Dive & References
Initial demonstration of a quantum heat engine based on dissipation-engineered superconducting circuits - Nature Communications, 2026
