World’s First Superconducting Quantum Heat Engine Could Power Bigger Quantum Computers

Scientists in Finland have developed the world’s first cyclic heat engine that works inside a superconducting quantum circuit. The tiny device can use a small amount of heat from a quantum refrigerator and convert it into useful work.

The breakthrough, achieved by researchers at Aalto University, could help make future quantum computers simpler, more affordable and easier to scale. In particular, it could reduce the huge number of microwave cables needed to connect thousands or even millions of quantum components.

The challenge of building larger quantum computers

Quantum computers use qubits, the basic units of quantum information. Unlike the bits in ordinary computers, qubits can exist in combinations of different states, allowing quantum computers to solve certain problems in ways that classical machines cannot.

However, building a large quantum computer is extremely difficult.

Finland’s Quantum Technology Strategy aims to develop a quantum computer with 1,000 logical qubits by 2035. Reaching this goal could require hundreds of thousands of physical qubits because several physical qubits may be needed to create one reliable logical qubit.

Connecting all these components is another major challenge. A large quantum computer could require millions of microwave cables to control and communicate with its qubits. At today’s prices, each cable can cost around €1,000.

That means the cables alone could add up to an enormous expense.

The cables also create another problem. They add complexity and can introduce unwanted noise into the extremely sensitive quantum system. Researchers at Aalto University therefore began looking for a different approach: could some of the functions normally handled by external cables be performed by tiny autonomous devices inside the quantum computer?

A heat engine at the quantum scale

The idea of a heat engine may sound far removed from quantum computing, but the basic principle is familiar.

Heat engines have played an important role in modern technology since the Industrial Revolution. Car engines, aircraft engines, ships and power plants all use heat to produce useful energy and perform work.

A conventional heat engine operates on a large scale. The Aalto University researchers wanted to demonstrate that a similar thermodynamic process could work at the scale of individual quantum systems.

Led by Mikko Möttönen, professor of quantum technology at Aalto University, the team built a microscopic heat engine using superconducting circuits.

The device was made using a combination of a transmon qubit, a resonator and a quantum-circuit refrigerator. It operated inside a cryostat, a system capable of maintaining temperatures extremely close to absolute zero.

“ In our experiment, we built a nanofabricated heat engine using superconducting circuits and operated it in a cryostat near absolute zero,” explained Tuomas Uusnäkki, who helped build the device.

The Otto cycle goes quantum

The researchers used an Otto cycle, a thermodynamic process commonly associated with internal-combustion engines such as those used in cars.

In simple terms, a heat engine takes energy in the form of heat, processes it through a cycle and converts part of that energy into useful work.

The researchers reproduced this basic idea inside their superconducting quantum circuit.

Instead of using a large quantity of heat, the quantum engine works with extremely small amounts of energy. The researchers controlled the flow of heat to and from the qubit and observed how the quantum system responded.

This allowed them to demonstrate that a thermodynamic engine can operate using a quantum system as its working substance.

One refrigerator for both heating and cooling

One of the most interesting features of the experiment is the role of the quantum-circuit refrigerator.

Unlike conventional systems that may require separate components for heating and cooling, the refrigerator used in the experiment can be controlled to do both.

“Our quantum-circuit refrigerator can be tuned to both heat and cool the qubit on demand,” Uusnäkki said. “Using carefully timed control pulses, we drove the engine in an Otto cycle and monitored the qubit state as the engine ran.”

This makes the system relatively simple and flexible.

By controlling the refrigerator and the qubit at precise times, the researchers were able to operate the engine through its thermodynamic cycle and measure its behavior.

Why this matters for quantum computers

The immediate achievement is scientific, but its potential applications are much broader.

Today's superconducting quantum computers depend heavily on microwave electronics and cables. These connections carry control signals between room-temperature equipment and quantum processors operating at temperatures close to absolute zero.

As quantum computers grow, the number of connections could become a serious engineering problem.

An autonomous quantum device could potentially perform certain operations locally, reducing the need for individual microwave cables running throughout the system.

This could lower hardware costs while also simplifying the architecture of future quantum computers.

For example, if some qubit-control or measurement functions could eventually be performed by autonomous quantum devices, manufacturers might not need to provide a separate external connection for every operation.

A step toward autonomous quantum machines

The current experiment is an important first step rather than a complete solution to the cabling problem.

The researchers' longer-term goal is to develop autonomous quantum heat engines capable of performing useful tasks without relying continuously on microwave pulses from external equipment.

Such devices could eventually help with functions such as reading or controlling qubits across a wide temperature range, potentially from near absolute zero toward room temperature.

Achieving that will require further research. Scientists will need to improve the efficiency, reliability and control of these microscopic engines and determine how they can be integrated into larger quantum processors.

Still, demonstrating a cyclic heat engine inside a superconducting circuit is a significant milestone.

The future of quantum computing

The development highlights an important shift in quantum technology. Building larger quantum computers is not simply about adding more qubits. Engineers must also find practical ways to control, connect, cool and read those qubits without making the entire system impossibly complicated.

Tiny autonomous quantum devices could become part of the answer.

If the technology can eventually reduce the need for millions of expensive microwave cables, the financial savings could be substantial. More importantly, reducing the number of external connections could make large quantum computers easier to build and operate.

The Aalto University team’s work therefore represents more than the creation of a tiny heat engine. It demonstrates that fundamental ideas from classical thermodynamics can be adapted to the quantum world—and potentially used to solve some of the biggest engineering challenges facing future quantum computers.

The research was published in the journal Nature.

Reference: Uusnäkki, T., Mörstedt, T., Teixeira, W. et al. Initial demonstration of a quantum heat engine based on dissipation-engineered superconducting circuits. Nat Commun 17, 6054 (2026). https://doi.org/10.1038/s41467-026-72651-x