Record-Breaking Quantum Refrigerator May Enable Reliable Quantum Computers

A new quantum refrigerator – represented by the square chip in the middle of a copper casing – relies on superconducting circuits and is powered by ambient heat. The illustration shows how the refrigerator leverages interactions between quantum bits, specifically between the target qubit and two auxiliary qubits used for cooling. It operates using energy flows driven by temperature differences between the quantum systems.

Quantum computers require extremely low temperatures to perform reliable calculations. One of the key challenges in advancing quantum computing is the difficulty of cooling components to temperatures close to absolute zero. Researchers from Chalmers University of Technology and the University of Maryland have now developed a minimal, self-governing refrigerator capable of cooling superconducting quantum bits (qubits) to record-low temperatures, paving the way for more reliable quantum computations.

Quantum Computing Challenges

Quantum computers have the potential to revolutionize fundamental technologies across various sectors, including medicine, energy, cryptography, artificial intelligence, and logistics. Unlike classical computers, where bits are either 1 or 0, quantum computers use qubits, which can exist in a superposition of both states simultaneously. This property enables quantum computers to perform parallel computations with immense processing potential. However, their operation is currently limited by the need to correct significant amounts of errors, which restricts the computing time of quantum systems.

Autonomous Quantum Cooling

According to Aamir Ali, a quantum technology researcher at Chalmers and lead author of a recent paper in Nature Physics, qubits are highly sensitive to environmental disturbances. “Weak electromagnetic waves leaking into the computer can randomly change the value of a qubit, causing errors that halt quantum calculations,” says Ali.

Quantum computers built with superconducting circuits can conduct electricity without resistance and efficiently store information. However, to function reliably over extended periods, qubits must be cooled to near absolute zero (-273.15°C). Current cryostats, which envelop quantum computers and use helium for cooling, can lower temperatures to approximately -273.1°C. Absolute zero is physically unattainable, but the new quantum refrigerator can complement existing cryostats by cooling systems several hundredths of a degree further, reaching record-low temperatures for superconducting qubits.

“The quantum refrigerator is based on superconducting circuits and powered by ambient heat, making it autonomous. It can cool qubits to approximately -273.13°C. This breakthrough paves the way for more reliable and error-free quantum computations while reducing the strain on hardware,” says Aamir Ali.

Surprising Performance

The quantum refrigerator utilizes interactions between qubits – specifically, between the qubit being cooled and two auxiliary qubits dedicated to the cooling process. It operates autonomously, relying on energy flows driven by temperature differences within the quantum systems. Once activated, the system functions without external intervention.

“Our work is undoubtedly the first demonstration of an autonomous quantum thermal machine performing a practically useful task. Initially, this experiment was intended as a proof of concept, so we were pleasantly surprised when the quantum refrigerator achieved unparalleled performance and succeeded in cooling the qubit to record-low temperatures,” says Simone Gasparinetti, Associate Professor at Chalmers and research leader for the study.

Details of the Research

The study, titled Thermally driven quantum refrigerator autonomously resets superconducting qubit, was published in Nature Physics. The compact quantum refrigerator, which fits on a small chip, was manufactured at Chalmers’ nanofabrication lab, Myfab.

The research team includes Mohammed Ali Aamir, Simone Gasparinetti, Claudia Castillo-Moreno, and Paul Jamet Suria from the Department of Microtechnology and Nanoscience at Chalmers, as well as Nicole Yunger Halpern, José Antonio Marín Guzman, and Jeffrey M. Epstein from the Joint Center for Quantum Information and Computer Science (NIST), the University of Maryland, and the Institute for Physical Science and Technology at the University of Maryland, USA.

The research was supported by the Swedish Research Council, the Knut and Alice Wallenberg Foundation through the Wallenberg Center for Quantum Technology (WACQT), the EU’s Quantum Flagship project ASPECTS, ERC ESQuAT, the National Science Foundation, and the John Templeton Foundation.