Record low temperatures for more reliable quantum computing

Quantum computing is a rapidly emerging technology with potentially revolutionary applications in medicine, energy, encryption, AI, and logistics. Quantum computers can solve problems that are too complex for classical computers thanks in part to a phenomenon called superposition. While the building blocks of a classical computer – bits – can take a value of either 0 or 1, the most common building blocks in quantum computers – qubits – can have a value of 0 and 1 simultaneously. This superposition enables quantum computers to perform parallel computations.

 

For qubits to work without errors and for longer periods, they need to be cooled to a cryogenic temperature close to absolute zero – zero Kelvin, equivalent to minus 273.15 degrees Celsius . The extreme cold puts the qubits into their lowest-energy state, the ground state, equivalent to value 0, a prerequisite for initiating a calculation.

Currently, dilution refrigerators are used to bring the qubits to about 50 millikelvin above absolute zero. Researchers at Chalmers University of Technology, Sweden, and the University of Maryland, USA, have developed a new type of quantum refrigerator that can complement the dilution refrigerator and autonomously cool superconducting qubits to a record low temperature of 22 millikelvin.

 

Operating principle of the quantum refrigerator

 

The quantum refrigerator is based on superconducting circuits and is powered by heat from the environment. It utilises interactions between the target qubit to be cooled and two quantum bits used for cooling. Next to one of the qubits, a warm environment is engineered to serve as a hot thermal bath. The hot thermal bath gives energy to one of the quantum refrigerator’s superconducting qubits and powers the quantum refrigerator.

The system is autonomous in that once it is started, it operates without external control and is powered by the heat that naturally arises from the temperature difference between two thermal baths.

 

The quantum refrigerator is described in an article published in Nature Physics.

 

Performance

 

With this method, researchers were able to increase the qubit’s probability to be in the ground state before computation to 99.97%, which is significantly better than what previous techniques could achieve, that is, between 99.8% and 99.92%. When performing multiple computations, this small difference compounds into a major performance boost in the efficiency of quantum computers.

 

The authors believe that this discovery paves the way for more reliable and error-free quantum computations that require less hardware overload.

 

 

Sources

Chalmers University of Technology. (2025, January 9). Record cold quantum refrigerator paves way for reliable quantum computers. ScienceDaily. Retrieved February 12, 2025 from www.sciencedaily.com/releases/2025/01/250109125828.htm

Aamir, M.A., Jamet Suria, P., Marín Guzmán, J.A. et al. Thermally driven quantum refrigerator autonomously resets a superconducting qubit. Nat. Phys. (2025). https://doi.org/10.1038/s41567-024-02708-5