Researchers from the universities of Melbourne and Manchester have invented a revolutionary technology for producing highly purified silicon that brings powerful quantum computers closer. A new technique for creating ultrapure silicon makes it an ideal material for building quantum computers at scale and with high precision, researchers say.

Increasing quantum coherence

Project co-leader Professor David Jamieson from the University of Melbourne said the innovation, published today (7 May 2024), said: Communication Material numbersmagazine NatureIt uses qubits composed of phosphorus atoms embedded in crystals of pure stable silicon and can overcome a critical hurdle to quantum computing by increasing the duration of this notoriously fragile crystal. quantum coherence .

“Fragile quantum coherence means that computational errors accumulate rapidly. “With the robust coherence provided by our new technique, quantum computers can solve in hours or minutes some problems that would take centuries for conventional or ‘classical’ computers, or even supercomputers,” Professor Jamieson said.

Quantum bits or qubits The building blocks of quantum computers are sensitive to small changes in their environment, including temperature fluctuations. Even when operating in silent refrigerators near absolute zero (minus 273 degrees Celsius), modern quantum computers can maintain error-free coherence for a fraction of a second.

University of Manchester co-chair Professor Richard Currie said ultrapure silicon enables the creation of high-performance qubit devices, a critical component needed to pave the way to scalable quantum computers.

“We have succeeded in creating a critical ‘brick’ needed to build a silicon quantum computer. This is an important step towards creating a technology that has the potential to be transformative for humanity,” Professor Currie said.

The role of silicon in quantum technologies

Lead author Ravi Acharya, a joint researcher at the University of Manchester and Cookson University in Melbourne, said the biggest advantage of quantum computing on silicon chips was that it used the same basic techniques used to make the chips used in modern computers.

“The electronic chips now found in everyday computers consist of billions of transistors — They can also be used to create qubits for silicon-based quantum devices. To date, the ability to create high-quality silicon qubits has been limited in part by the purity of the starting silicon material. The revolutionary naivety we show here solves this problem.”

Professor Jamieson said the new highly purified silicon computer chips contain and protect qubits so they can maintain quantum coherence for much longer, allowing complex calculations to be carried out with much less need for error correction.

“Our technique paves the way for reliable quantum computers that promise incremental changes across society, including artificial intelligence, secure data and communications, vaccine and drug development, energy use, logistics and manufacturing,” he said.

Made from beach sand, silicone is an important material for today’s information technology industry because it is widespread and versatile. a semiconductor : It can act as a conductor or insulator of electric current, depending on other chemical elements added to it.

Silicon purification for quantum computing

“The problem is that although naturally occurring silicon is predominantly the preferred isotope of silicon-28, it also contains about 4.5 percent of silicon-29. “In the nucleus of each atom of silicon-29, which acts like a tiny magnet, it maintains quantum coherence. “There’s an extra neutron that distorts and creates calculation errors,” he said.

The researchers aimed a focused, high-speed beam of pure silicon-28 at the silicon chip, so that the silicon-28 gradually replaced the silicon-29 atoms in the chip, reducing the silicon-29 content from 4.5 percent to two parts per million. (0.0002 percent). ).

“The great news is that to purify silicon to this level we can now use a standard machine (an ion implanter) that you can find in any semiconductor manufacturing laboratory, tuned to the specific configuration we have designed,” Professor Jamieson said. .