Scientists at Aalto University have successfully created and operated the world’s first cyclic quantum heat engine built within a superconducting circuit, marking a significant milestone in quantum physics research. The breakthrough represents an important convergence of two traditionally separate scientific domains: quantum mechanics, which governs behavior at subatomic scales, and thermodynamics, which describes energy and heat transfer in larger systems. The experiment addresses fundamental questions about how thermodynamic processes behave when quantum phenomena such as tunneling, entanglement, and superposition become relevant.
The device operates by recreating an Otto cycle—a thermodynamic process also used in conventional engines like those in automobiles—within a superconducting circuit cooled near absolute zero. At its core is a transmon qubit, a fundamental component of modern quantum technology, connected to a quantum circuit refrigerator. This refrigerator can be tuned to both heat and cool the qubit on demand, allowing researchers to control heat flow at the quantum scale. Using precisely timed control pulses, the team demonstrated that heat passing through the qubit during the cycle was converted into measurable positive work, achieving the cyclic operation that has been a key objective for quantum heat engine researchers.
The findings have potential implications for the development of large-scale quantum computers. As quantum computing systems scale up, they face significant engineering challenges, including the need for millions of expensive microwave cables to connect superconducting circuits at millikelvin temperatures to room-temperature control equipment. These cables add cost, complexity, and introduce unwanted noise into quantum systems. Autonomous quantum devices integrated directly into superconducting circuits could eventually reduce or eliminate much of this cabling infrastructure.
Researchers are now working to refine the design and develop a fully autonomous version of the heat engine. One potential application would involve reading qubits without requiring microwave pulses to travel from near absolute zero temperatures to room temperature. Such autonomous devices could prove particularly valuable as quantum computers grow substantially larger, potentially helping to realize ambitious goals such as the development of machines with hundreds of thousands of physical qubits. The study was published in Nature Communications and conducted using Finland’s national research infrastructure for nanotechnology and quantum technology.
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