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Scientists Achieve 'Transformational' Breakthrough in Scaling Quantum Computers

2 FEBRUARY 2021

Scientists have developed a new kind of cryogenic computer chip capable of functioning at temperatures so cold, it approaches the theoretical limit of absolute zero.

This cryogenic system, called Gooseberry, lays the groundwork for what could be a revolution in quantum computing – enabling a new generation of machines to perform calculations with thousands of qubits or more, whereas today's most advanced devices comprise only dozens.

 

"The world's biggest quantum computers currently operate with just 50 or so qubits," explains quantum physicist David Reilly from the University of Sydney and Microsoft's Quantum Laboratory.

"This small scale is partly because of limits to the physical architecture that control the qubits."

That physical architecture is constrained because of the extreme conditions qubits need to perform quantum mechanical calculations.

010 quantum gooseberry 1The Gooseberry chip (red) next to a qubit test chip (blue) and resonator chip (purple). (Microsoft)

Unlike the binary bits in traditional computers, which take either a 0 or 1 value, qubits occupy what is known as the quantum superposition – an undefined and unmeasured state that can effectively represent both 0 and 1 at the same time in the context of a larger mathematical operation.

This esoteric principle of quantum mechanics means quantum computers can theoretically solve vastly complex mathematical problems that classic computers would never be able to answer (or take years trying).

Like with conventional technology, though, more is always better, and to date, researchers have been limited in how many qubits they've been able to successfully deploy into quantum systems.

 

One of the reasons for that is qubits need extreme levels of cold to function (in addition to other controlled conditions), and the electrical wiring used in today's quantum computer systems inevitably output small but sufficient levels of heat that disrupt the thermal requirements.

Scientists are looking into ways to get around that, but many quantum innovations to date have depended on contriving bulky wiring rigs to keep temperatures stable for increasing qubit counts, but that solution has its own limits.

"Current machines create a beautiful array of wires to control the signals; they look like an inverted gilded birds' nest or chandelier," Reilly says.

"They're pretty, but fundamentally impractical. It means we can't scale the machines up to perform useful calculations. There is a real input–output bottleneck."

The solution to that bottleneck could be Gooseberry: a cryogenic control chip that can operate at 'millikelvin' temperatures just a tiny fraction of a degree above absolute zero, as described in a new study.

That extreme thermal capacity means it can sit inside the super-cold refrigerated environment with the qubits, interfacing with them and passing signals from the qubits to a secondary core that sits outside in another extremely cold tank, immersed in liquid helium.

 

In doing so, it removes all the excess wiring and the surplus heat they generate, meaning contemporary qubit bottlenecks in quantum computing could soon be a thing of the past.

"The chip is the most complex electronic system to operate at this temperature," Reilly explained to Digital Trends.

"This is the first time a mixed-signal chip with 100,000 transistors has operated at 0.1 kelvin, [the equivalent to] –459.49-degrees Fahrenheit, or –273.05-degrees Celsius."

Ultimately, the team expects their system could enable thousands of qubits to be controlled by the cryogenic chip – roughly a 20-fold increase in what's possible today. In the future, the same sort of approach might enable quantum computers on a whole other level.

"Why not start thinking about billions of qubits?" Reilly told the Australian Financial Review. "The more qubits we can control, the better."

While it may be some time before we see this cryogenic breakthrough put to practical use outside the lab, there's no doubting we're looking at a big step forward in quantum computing, experts say.

"This is going to be transformational in the next few years," Andrew White, the director of the ARC Centre of Excellence for Engineered Quantum Systems, who wasn't involved with the study but oversees quantum research in Australia, told ABC News.

"If everyone [developing quantum computers] isn't using this chip, they will be using something inspired by it."

The findings are reported in Nature Electronics.