First Superconducting Quantum Heat Engine Developed by Aalto University Researchers

Researchers at Aalto University have successfully created the world’s first superconducting quantum heat engine, marking a significant advancement in both quantum technology and thermodynamics. This engine operates within a superconducting circuit and is designed to enhance our understanding of thermodynamic principles by merging quantum mechanics with classical thermodynamics.

The innovative engine operates under ultracold conditions and utilizes a combination of a transmon qubit, resonator, and quantum refrigerator to convert a minimal amount of available heat into measurable positive work. Academy Professor Mikko Möttönen, who led the study, emphasized that achieving cyclic operation has been a crucial goal for researchers focused on quantum heat engines, providing a novel proof of concept for future superconducting heat engines in quantum computing.

Recreating an Otto Cycle Near Absolute Zero

To demonstrate the engine’s operation, the researchers replicated an Otto cycle within the superconducting circuit, a process commonly used in traditional car engines and machinery. First author Tuomas Uusnäkki explains, “In our experiment, we built a nanofabricated heat engine using superconducting circuits and operated it in a cryostat near absolute zero, with a transmon qubit at its core.”

The design allows the same quantum refrigerator to simultaneously provide both heating and cooling for the qubit, a departure from conventional heat engines that typically rely on separate environments. “Our quantum-circuit refrigerator can be tuned to both heat and cool the qubit on demand,” states Uusnäkki, who detailed how carefully timed control pulses drove the engine through the Otto cycle while monitoring the qubit’s state.

Measurements indicated that the heat moving through the qubit during the cycle successfully produced positive work, demonstrating the engine’s effectiveness.

Path Towards Autonomous Quantum Computers

The research team is gearing up to refine the engine’s design with the aim of developing a fully autonomous heat engine. Such technology may facilitate the reading out of qubits without needing to transmit a microwave pulse across extreme temperature differentials.

As quantum computing technology evolves, this capability could significantly reduce complexity and costs. Möttönen highlighted that Finland’s Quantum Technology Strategy envisions a quantum computer with a thousand logical qubits by 2035, which would necessitate hundreds of thousands of physical qubits and currently demands millions of costly microwave cables. He noted that the existing system introduces noise that could be eliminated by leveraging autonomous devices.

The groundbreaking experiment was conducted at OtaNano, Finland’s nationally supported research infrastructure for nano, micro, and quantum technology, with funding from the Research Council of Finland and the Finnish Cultural Foundation. The study results were published in Nature Communications.