Scientists at Aalto University have successfully built and operated the world’s first superconducting quantum heat engine, advancing understanding of how thermodynamic principles function at quantum scales. The breakthrough demonstrates that familiar thermodynamic processes can operate effectively when quantum effects such as tunneling, entanglement, and superposition come into play, bridging two areas of physics that typically describe vastly different size scales.
The experimental device combines a transmon qubit, a resonator, and a quantum refrigerator operating at near absolute-zero temperatures. Researchers reproduced an Otto cycle—a thermodynamic process also found in conventional car engines and machinery—within the superconducting circuit. By connecting the qubit to a quantum circuit refrigerator, the team gained precise control over heat flow at quantum scales and demonstrated the conversion of heat into measurable work. The key innovation involved using a single quantum refrigerator to supply both heating and cooling functions, simplifying the system compared to conventional engines requiring separate hot and cold environments.
Measurements confirmed that the cyclic operation successfully produced positive work from the heat passing through the qubit during each cycle. This proof of concept provides crucial validation for the feasibility of superconducting heat engines in quantum technology applications. The research, led by Academy Professor Mikko Möttönen and first-authored by Tuomas Uusnäkki, was published in Nature Communications.
Looking forward, researchers plan to refine the design toward a fully autonomous heat engine that could be integrated directly into superconducting circuits. Such autonomous devices could dramatically reduce the complexity and expense of large-scale quantum computers by eliminating the need for extensive microwave cable connections. Current approaches to building quantum systems with thousands of qubits would require millions of expensive microwave cables that also introduce unwanted noise. Autonomous quantum devices embedded in circuits could address both the hardware requirements and noise challenges simultaneously, supporting efforts like Finland’s Quantum Technology Strategy to develop quantum computers with substantial qubit counts.
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