Researchers at Aalto University have created the first cyclic quantum heat engine embedded within a superconducting circuit. The tiny device, smaller than a grain of sand, converts heat into useful work at temperatures near absolute zero by using a qubit—the fundamental unit of quantum information—as its working medium, repeatedly cycling it through heating, cooling, and energy-conversion stages.

Led by Academy Professor Mikko Möttönen and published in Nature Communications, the study adapts the familiar concept of a heat engine to the quantum realm. Like conventional engines that generate useful work by transferring energy between hot and cold reservoirs, the Aalto device operates on the same fundamental principle, but at a microscopic scale where energy is governed by the laws of quantum mechanics.

Figure 1. Concept Illustration of a Superconducting Quantum Heat Engine.

How a Qubit Can Function as a Heat Engine

The engine is built around a flux-tunable transmon qubit connected to a resonator and a quantum circuit refrigerator. Transmon qubits are commonly used in superconducting quantum computers because they can store and manipulate quantum information while being controlled with microwave signals. Figure 1 shows Concept Illustration of a Superconducting Quantum Heat Engine.

Instead of using separate hot and cold reservoirs, the researchers used the refrigerator in two opposite modes, switching it between heating and cooling the qubit. By changing the qubit’s energy level at precisely timed moments, they carried the system through the four stages of a quantum Otto cycle.

While the Otto cycle is the same thermodynamic principle that powers many gasoline engines, the working substance in this experiment was not a gas in a cylinder. It was a single qubit exchanging tiny amounts of energy within a cryogenic superconducting circuit operating near absolute zero.

According to first author Tuomas Uusnäkki, the team created a nanofabricated heat engine from superconducting circuits and successfully operated it in a cryostat, with the transmon qubit serving as the core energy-converting element.

Tracking Heat, Work, and Efficiency in a Quantum Engine

The researchers initialized the qubit in a thermal state and operated the engine for up to three consecutive cycles. Using single-shot measurements, they monitored the qubit’s state throughout the process and determined how much heat the engine absorbed, how much work it generated, and its overall efficiency.

By tuning a quantum-circuit refrigerator to alternately heat and cool the qubit and applying precisely timed control pulses, the team drove the system through an Otto cycle while continuously tracking its quantum state.

The results showed that the device generated positive work, rather than simply redistributing heat within the circuit. The measured power output and efficiency closely matched theoretical simulations, confirming that the system functioned as a true cyclic quantum heat engine.

According to first author Tuomas Uusnäkki, this represents the first experimental demonstration of a cyclic quantum heat engine in superconducting circuits, with the additional advantage that a single controllable quantum refrigerator can serve as both the hot and cold reservoir, making the setup simpler and more flexible.

Why Superconducting Circuits are Important

Quantum heat engines have previously been realized in platforms such as trapped ions, ultracold atomic gases, nuclear spins, and diamond defects. Superconducting circuits are particularly significant because they are already one of the leading technologies for quantum computing, communication, and sensing. Until this study, however, no experiment had demonstrated a fully cyclic quantum heat engine operating within a superconducting circuit.

The key advance is not the tiny amount of work produced by the device, but the proof that heat can be intentionally manipulated and converted into useful work within the same circuitry used to build quantum processors. This establishes a new level of thermodynamic control directly inside superconducting quantum hardware.

As superconducting quantum computers scale up, managing the enormous number of microwave connections between room-temperature electronics and processors operating near absolute zero becomes a major challenge. Each cable increases cost, occupies valuable space, and can introduce unwanted heat and electrical noise into the quantum system.

The Aalto team is therefore pursuing a fully autonomous quantum heat engine that could perform certain control tasks directly inside the cryogenic circuit. One proposed use is reading a qubit’s state without transmitting microwave signals back to room-temperature equipment. Integrating more control and measurement functions within the cold quantum hardware could dramatically reduce the amount of external wiring required.

Mikko Möttönen notes that Finland’s quantum technology roadmap aims for a machine with 1,000 logical qubits by 2035, which could require hundreds of thousands of physical qubits [1]. Achieving that scale with current approaches would demand millions of expensive microwave cables while also increasing noise in the processor. Autonomous cryogenic devices could largely eliminate that wiring burden and make large-scale superconducting quantum computers more practical.

References:

1. https://scitechdaily.com/worlds-first-superconducting-quantum-heat-engine-could-transform-quantum-computing/

Cite this article:

Janani R (2026), First Superconducting Quantum Heat Engine Could Revolutionize Quantum Computing, AnaTechMaz, pp.546.