Freezing Time: The Revolutionary Tech Behind Reliable Quantum Computing

By Chalmers University of Technology January 13, 2025

Collected at: https://scitechdaily.com/freezing-time-the-revolutionary-tech-behind-reliable-quantum-computing/

A groundbreaking quantum refrigerator cools qubits autonomously, enhancing quantum computation precision and reducing errors.

Quantum computers need extremely cold temperatures to operate reliably. A major hurdle in making quantum computers practical is the challenge of cooling qubits to temperatures near absolute zero. Researchers from Chalmers University of Technology in Sweden and the University of Maryland in the USA have developed an innovative refrigerator capable of autonomously cooling superconducting qubits to record-low temperatures. This breakthrough could significantly enhance the reliability of quantum computations, bringing the technology closer to widespread use.

Revolutionary Potential of Quantum Computing

Quantum computers have the potential to transform key technologies across sectors like medicine, energy, encryption, artificial intelligence, and logistics. Unlike classical computers, which use bits that represent either 0 or 1, quantum computers rely on qubits, which can represent both 0 and 1 simultaneously due to a phenomenon known as superposition. This unique property is one of the reasons why a quantum computer can perform parallel computations, unlocking extraordinary computational power. However, their performance is still limited by the time they must spend correcting errors, which significantly constrains their operational efficiency.

“Qubits, the building blocks of a quantum computer, are hypersensitive to their environment. Even extremely weak electromagnetic interference leaking into the computer could flip the value of the qubit randomly, causing errors – and subsequently hindering quantum computation,” says Aamir Ali, research specialist in quantum technology at Chalmers University of Technology.

Advances in Quantum Cooling Technology

Today, many quantum computers are based on superconducting electrical circuits that have zero resistance and therefore preserve information very well. For qubits to work without errors and for longer periods in such a system, they need to be cooled to a temperature close to absolute zero, equivalent to minus 273.15 degrees Celsius or zero Kelvin, the scientific unit of temperature. The extreme cold puts the qubits into their lowest-energy state, the ground state, equivalent to value 0, a prerequisite for initiating a calculation.

The cooling systems used today, so-called dilution refrigerators, bring the qubits to about 50 millikelvin above absolute zero. The closer a system approaches to absolute zero, the more difficult further cooling is. In fact, according to the laws of thermodynamics, no finite process can cool any system to absolute zero. Now, the researchers at Chalmers University of Technology and University of Maryland have constructed a new type of quantum refrigerator that can complement the dilution refrigerator and autonomously cool superconducting qubits to record-low temperatures. The quantum refrigerator is described in an article published on January 9 in the journal Nature Physics.

“The quantum refrigerator is based on superconducting circuits and is powered by heat from the environment. It can cool the target qubit to 22 millikelvin, without external control. This paves the way for more reliable and error-free quantum computations that require less hardware overload,” says Aamir Ali, lead author of the study and continues:

“With this method, we were able to increase the qubit’s probability to be in the ground state before computation to 99.97 percent, which is significantly better than what previous techniques could achieve, that is, between 99.8 and 99.92 percent. This might seem like a small difference, but when performing multiple computations, it compounds into a major performance boost in the efficiency of quantum computers.”

Innovations in Quantum Refrigeration

The refrigerator utilizes interactions between different qubits, specifically 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.

“Energy from the thermal environment, channeled through one of the quantum refrigerator’s two qubits, pumps heat from the target qubit into the quantum refrigerator’s second qubit, which is cold. That cold qubit is thermalized to a cold environment, into which the target qubit’s heat is ultimately dumped,” says Nicole Yunger Halpern, NIST Physicist and Adjunct Assistant Professor of Physics and IPST at the University of Maryland, USA.

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.

“Our work is arguably the first demonstration of an autonomous quantum thermal machine executing a practically useful task. We originally intended this experiment as a proof of concept, so we were pleasantly surprised when we found out that the performance of the machine surpasses all existing reset protocols in cooling down the qubit to record-low temperatures,” says Simone Gasparinetti, Associate Professor at Chalmers University of Technology and lead author of the study.

For more on this research, see Supercold Qubits: The Key to Error-Free Quantum Computing.

Reference: “Thermally driven quantum refrigerator autonomously resets a superconducting qubit” by Mohammed Ali Aamir, Paul Jamet Suria, José Antonio Marín Guzmán, Claudia Castillo-Moreno, Jeffrey M. Epstein, Nicole Yunger Halpern and Simone Gasparinetti, 9 January 2025, Nature Physics.
DOI: 10.1038/s41567-024-02708-5