Researchers at Aalto University have demonstrated the world’s first cyclic quantum heat engine built inside a superconducting circuit, according to a study published July 13 in Nature Communications. Led by Academy Professor Mikko Möttönen, the experiment successfully reproduced an Otto cycle near absolute zero to convert miniscule amounts of heat into measurable positive work, marking a crucial step toward autonomous hardware for scalable quantum computers.
Building the First Superconducting Quantum Heat Engine
Bridging microscopic quantum mechanics and macroscopic thermodynamics has long challenged physicists. While quantum mechanics governs particles below atomic scales, thermodynamics measures heat and energy across larger systems. The new device tackles this by combining a transmon qubit, a resonator, and a quantum refrigerator, according to the study’s findings.
“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.
Did you know? The Otto cycle used in this quantum engine is the same thermodynamic process that powers conventional car engines, though operating here under ultracold quantum conditions.
Recreating the Otto Cycle Near Absolute Zero
Traditional heat engines require separate hot and cold environments. However, the Aalto University setup utilizes a single quantum circuit refrigerator connected to the transmon qubit, allowing researchers to control heat flow on demand using carefully timed control pulses, as explained by Uusnäkki.
Measurements of the qubit state during these cycles confirmed that heat passing through the system produced positive work. “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,” Uusnäkki states.
Scaling Quantum Computers Without Millions of Cables
Looking ahead, the research team aims to refine the design to build a fully autonomous heat engine. According to Möttönen, this capability could eliminate the need to carry microwave pulses from millikelvin temperatures up to room temperature, solving a major bottleneck for large-scale hardware.
Finland’s Quantum Technology Strategy targets a computer with one thousand logical qubits by 2035, translating to hundreds of thousands of physical qubits. Meeting this goal with current methods requires millions of expensive microwave cables that also introduce unwanted noise. Integrating autonomous devices directly into superconducting circuits could bypass these wiring challenges entirely.
The pioneering experiment was conducted at 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.
Frequently Asked Questions
What is a quantum heat engine?
It is a microscopic device that converts heat into useful work under ultracold quantum conditions, applying thermodynamic cycles like the Otto cycle to quantum systems.
How does this technology help quantum computers?
According to Aalto University researchers, autonomous heat engines integrated into superconducting circuits could eventually replace thousands of microwave cables, reducing both system noise and hardware complexity.
Who led the study?
The research was led by Academy Professor Mikko Möttönen and published in Nature Communications, with Tuomas Uusnäkki serving as the study’s first author.
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