Quantum computers are poised to revolutionize a wide array of industries, from medicine and energy to encryption, artificial intelligence, and logistics. These advanced computers leverage the unique properties of quantum mechanics to solve problems that are currently intractable for classical computers. The foundation of quantum computers lies in qubits, the quantum analog of classical bits. While classical bits are binary and can only be in one of two states—0 or 1—qubits can exist in multiple states at once due to the phenomenon known as superposition. This enables quantum computers to perform parallel computations, greatly increasing their computational power.
However, for quantum computers to function properly and maximize their potential, the qubits must be maintained under highly controlled conditions, particularly at extremely low temperatures. The delicate nature of qubits makes them highly sensitive to external noise, including electromagnetic interference, which can easily flip the state of a qubit, introducing errors into quantum computations. A primary challenge in realizing fully functional quantum computers, therefore, is creating a stable environment in which qubits can work reliably.
The temperature at which quantum computers operate is crucial to minimizing such errors. Many modern quantum computers use superconducting qubits, which require extreme cooling to operate. Superconducting materials, which exhibit zero electrical resistance, preserve the information stored in qubits, making them ideal for quantum computation. However, for superconducting qubits to work effectively and remain error-free for long enough to perform useful calculations, they must be cooled to temperatures that are as close as possible to absolute zero.
Reaching such low temperatures is not simple. Theoretically, absolute zero (0 Kelvin, -273.15°C) is the point where all atomic motion stops, and achieving this temperature is essentially impossible according to the laws of thermodynamics. Nevertheless, researchers have devised cooling systems such as dilution refrigerators to bring the temperature of the qubits down to approximately 50 millikelvin, just above absolute zero. However, the cooling system’s efficiency becomes progressively more challenging as the temperature nears absolute zero, with no finite process being capable of cooling a system down to this ultimate limit.
To overcome these limitations, researchers at Chalmers University of Technology in Sweden and the University of Maryland in the U.S. have engineered a breakthrough in quantum refrigeration that promises to accelerate the development of practical quantum computers. These researchers have created a new type of quantum refrigerator capable of autonomously cooling superconducting qubits to record-low temperatures. This new refrigerator technology marks a significant advancement by increasing the reliability and precision of quantum systems, ultimately paving the way for more effective and less error-prone quantum computations.
The newly developed quantum refrigerator relies on a novel mechanism to extract heat from qubits and lower their temperatures. While conventional dilution refrigerators require external intervention to cool the system, the quantum refrigerator designed by Chalmers University and University of Maryland researchers is powered naturally by the heat generated from the thermal environment. This innovation not only simplifies the process but also makes the cooling process more efficient.
The quantum refrigerator in question is based on superconducting circuits. Superconducting materials are crucial to quantum computing because they offer no electrical resistance, which is essential for preserving qubit states. The refrigerator works by utilizing interactions between the target qubit (the one to be cooled) and two other qubits that are used in the cooling process. One of these qubits interacts with the thermal environment, absorbing energy from the surroundings. The energy gained by the first qubit is transferred to the second qubit, which is placed in a cold environment that acts as a heat sink. This interaction effectively lowers the temperature of the target qubit.
Once the system is initialized, the quantum refrigerator operates autonomously without needing external control. It is powered solely by the energy from the temperature difference between the two thermal baths, meaning it can function independently as long as the initial cooling mechanism is in place. This represents a major leap forward in quantum technology, demonstrating the first autonomous quantum thermal machine that performs a useful task.
The implications of this development are profound. In traditional quantum computers, maintaining the stability of qubits has been a significant limitation. Qubits, being highly sensitive to external influences, tend to lose their coherence quickly, which leads to errors and limits their computational capacity. The new quantum refrigerator, however, enhances the probability that a qubit remains in its ground state—the lowest energy state—by effectively cooling the qubit to 22 millikelvin, which significantly improves its reliability. Previously, researchers could achieve ground-state probabilities of around 99.8 to 99.92%, but with the new technology, this figure has been increased to an impressive 99.97%.
This might seem like a small improvement, but when scaled to larger systems where many qubits are used for complex calculations, even minor improvements in stability can lead to major performance gains. The increased probability of qubits staying in their ground state enables quantum computers to perform longer calculations with fewer errors, which is a crucial requirement for making quantum computation viable for practical applications in the future.
The researchers at Chalmers and Maryland also point out that the quantum refrigerator system can significantly reduce the need for excessive hardware, which would otherwise be necessary to cool qubits in traditional systems. In other words, the autonomous nature of the refrigerator reduces the overall infrastructure complexity while improving the accuracy and reliability of quantum computers.
The refrigerator was designed and fabricated in Myfab, Chalmers University of Technology’s nanofabrication laboratory, and the results of their research were published in the journal Nature Physics under the title “Thermally driven quantum refrigerator autonomously resets a superconducting qubit.” The experimental success in this study is considered a proof of concept, but the results have far exceeded initial expectations. The method devised by the researchers represents a significant step toward overcoming the temperature constraints that have long held back the development of scalable and efficient quantum computing.
Looking ahead, the breakthrough in autonomous quantum refrigeration brings us one step closer to making quantum computers a practical reality for society. With applications ranging from the creation of new medicines and more efficient energy storage systems to advancements in artificial intelligence and the development of ultra-secure encryption methods, the potential societal impact of quantum computing is enormous. By solving fundamental issues like qubit stability and temperature control, this innovation will allow quantum computers to run more reliably, enabling broader deployment across industries and sectors that can benefit from their computational power.
Reference: Thermally driven quantum refrigerator autonomously resets a superconducting qubit, Nature Physics (2025). DOI: 10.1038/s41567-024-02708-5