Scientists have taken an important step toward more powerful quantum computers by creating the world’s first superconducting quantum heat engine.
The tiny device, developed by researchers at Aalto University in Finland, shows that heat can be controlled and turned into useful work inside a superconducting quantum circuit.
The breakthrough could eventually make future quantum computers simpler, cheaper, and more efficient.
The study, published in Nature Communications, also gives scientists a new way to explore quantum thermodynamics, a growing field that combines the laws of heat and energy with the strange behavior of quantum mechanics.
Thermodynamics explains how heat is converted into useful energy. It is the science behind familiar machines such as steam engines, car engines, and power plants.
Quantum mechanics, on the other hand, describes how matter behaves at incredibly small scales, where particles can display unusual properties such as superposition and quantum tunneling.
Researchers have long wondered how these two areas of physics work together. Building a quantum heat engine provides a practical way to study that question while also creating technology that could benefit future quantum devices.
The research team built a miniature heat engine inside a superconducting circuit cooled to temperatures just above absolute zero. At the center of the device is a transmon qubit, one of the key building blocks used in many quantum computers today.
The engine follows an Otto cycle, the same basic thermodynamic cycle used in many car engines. Instead of burning fuel, however, it uses tiny amounts of heat that exist even under ultracold quantum conditions.
To make the engine work, the researchers connected the qubit to a quantum-circuit refrigerator, a special device that can either heat or cool the qubit when needed. By carefully controlling this process with precisely timed pulses, they guided the engine through repeated operating cycles and monitored its behavior.
The experiments showed that heat flowing through the qubit was successfully converted into positive work. According to the researchers, this is the first successful demonstration of a cyclic quantum heat engine built with superconducting circuits.
One unusual feature of the design is that the same quantum refrigerator acts as both the hot and cold source for the engine. Traditional heat engines require separate hot and cold reservoirs, but this approach makes the system much simpler and more flexible.
The researchers are already working on the next stage of the technology. Their goal is to build a fully autonomous quantum heat engine that can perform tasks inside a quantum computer without relying on large numbers of external microwave cables.
Reducing the need for these cables could become increasingly important as quantum computers continue to grow. Large-scale quantum systems may eventually require hundreds of thousands of physical qubits, and today’s designs would need millions of expensive cables that also introduce unwanted noise into the system.
If autonomous quantum heat engines can replace much of this wiring, they could help pave the way for larger, more practical quantum computers while also deepening our understanding of how the laws of thermodynamics operate in the quantum world.
