World's First Superconducting Quantum Heat Engine Runs on Heat Near Absolute Zero

Aalto University researchers have demonstrated the first cyclic quantum heat engine inside a superconducting circuit: a transmon qubit connected to a quantum-circuit refrigerator that harnesses the minuscule heat present near absolute zero to produce useful work. Published in Nature Communications, the proof of concept could lead to autonomous devices that slash the thousands of expensive microwave cables needed for high-qubit quantum computers.

Key Takeaways

Aalto University researchers have demonstrated the first cyclic quantum heat engine inside a superconducting circuit: a transmon qubit connected to a quantum-circuit refrigerator that harnesses the minuscule heat present near absolute zero to produce useful work.
Published in Nature Communications, the proof of concept could lead to autonomous devices that slash the thousands of expensive microwave cables needed for high-qubit quantum computers.

AI synthesis3 sources7

Heat engines powered the industrial revolution, converting heat into useful work. Now physicists have built the first cyclic quantum heat engine inside a superconducting circuit — a tiny device that harnesses the minuscule heat present near absolute zero to produce positive work.

The experiment, led by Academy Professor Mikko Möttönen at Aalto University and published in Nature Communications, uses a transmon qubit — one of the basic building blocks of modern quantum computers — connected to a quantum-circuit refrigerator. Unlike a classical engine, which needs separate hot and cold reservoirs, the quantum refrigerator can be tuned to both heat and cool the qubit on demand. Using carefully timed control pulses, the team drove the device through an Otto cycle, the same thermodynamic process that powers car engines, and watched the heat flowing through the qubit generate positive work.

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

The team's motivation is practical: a fully autonomous engine on a chip could read out qubits without routing microwave pulses between millikelvin temperatures and room temperature. Today, Finland's goal of a quantum computer with one thousand logical qubits by 2035 would probably require hundreds of thousands of physical qubits — and with current technology, millions of microwave cables, each costing thousands of euros. The cables also inject noise. "Using autonomous devices instead would mostly eliminate the need for those cables," said Möttönen.

Beyond quantum computing, the result advances the young field of quantum thermodynamics — how the strange phenomena of quantum mechanics, such as entanglement and superposition, mix with the stolid certainties of classical engines. The researchers used OtaNano, Finland's national research infrastructure for nano-, micro- and quantum technology.