The new chip design describes a novel architecture that allows quantum calculations to be performed using conventional existing complementary metal-oxide-semiconductor (CMOS) components. According to the researchers, the new design offers the potential – for the first time – toward a conceivable engineering pathway for creating millions of quantum bits, or qubits.
“With quantum computing, we are on the verge of another technological leap that could be as deep and transformative [as the creation of the modern-day microprocessor],” says Andrew Dzurak, director of the Australian National Fabrication Facility at UNSW. “But a complete engineering design to realize this on a single chip has been elusive. I think what we have developed at UNSW now makes that possible. And most importantly, it can be made in a modern semiconductor manufacturing plant.”
“Remarkable as they are, today’s computer chips cannot harness the quantum effects needed to solve the really important problems that quantum computers will,” he says. “To solve problems that address major global challenges – like climate change or complex diseases like cancer – it’s generally accepted we will need millions of qubits working in tandem. To do that, we will need to pack qubits together and integrate them, like we do with modern microprocessor chips. That’s what this new design aims to achieve.”
Based on silicon spin qubits, the researchers’ design uses conventional silicon transistor switches to “turn on” operations between qubits in a vast two-dimensional array, using a grid-based “word” and “bit” select protocol similar to that used to select bits in conventional computer memory chips. By selecting electrodes above a qubit, says Dzurak, a qubit’s spin – which stores the quantum binary code of a 0 or 1 – can be controlled, and by selecting electrodes between the qubits, two-qubit logic interactions – or calculations – can be performed between qubits.
A quantum computer uses “spooky” principles of quantum physics – i.e., entanglement and superposition – to exponentially expand beyond the binary code vocabulary used in modern computers. Qubits can store a 0, a 1, or an arbitrary combination of 0s and 1s at the same time, as well as process them simultaneously, doing multiple operations at once, allowing a universal quantum computer – a goal dubbed by some as the “space race of the 21st century” – to be millions of times faster than any conventional computer.
However, says Dzurak, in order to solve complex problems, a useful universal quantum computer will need a large number of qubits – possibly millions – because, due to their quantum nature, qubits are fragile and prone to data loss. As a result, even tiny errors can be quickly amplified into wrong answers.
“So we need to use error-correcting codes which employ multiple qubits to store a single piece of data,” Dzurak says. “Our chip blueprint incorporates a new type of error-correcting code designed specifically for spin qubits, and involves a sophisticated protocol of operations across the millions of qubits. It’s the first attempt to integrate into a single chip all of the conventional silicon circuitry needed to control and read the millions of qubits needed for quantum computing.”
According to the researchers, they have been testing elements of their design in the lab, with “very positive results.” For more, see “Silicon CMOS architecture for a spin-based quantum computer.”
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