Three breakthrough papers published in just the past year have confirmed that silicon is neck-and-neck with competing technology for quantum computing, including those under active research by corporate giants Google, Microsoft and IBM.
Creating the quantum entangled pairs that form the qubits, the heart of quantum computation, has thus far required the use of complex, exotic materials and structures, such as from honeycomb boron nitride and trapping molecules in lasers.
Although these techniques are incredibly promising they have one significant downside – throwing away the trillions of dollars and decades of research and development invested in the traditional computing material, silicon.
Now an Australian team led by Andrew Dzurak from the University of New South Wales (UNSW) has made a series of breakthroughs that have suddenly made silicon a leading focus for materials research quantum computer development.
Qubits hold great promise, but unlike bits in traditional computing, they are error prone. This means millions are required for complex calculations to allow for error correction.
Using existing techniques for forming quantum entangled pairs, any potential quantum computer would be unfeasibly large. That’s why three recent papers by the UNSW researchers are so important.
The first, published in the journal Nature Electronics, showed silicon reaching an accuracy (or fidelity) for one-qubit logic of 99.96%.
“This puts it on an even par with all other competing qubit technologies”, explains Dzurak, “since all qubits have errors, and these must be kept very low if we want to do useful computations, otherwise the final answers to calculations will be unreliable.”
The result was followed up by a second paper, in the journal Nature, which demonstrated that two-qubit computations had reached 98% accuracy, an important step because linking qubits together is how quantum computations are undertaken.
“We think that we’ll achieve significantly higher fidelities in the near future, opening the path to full-scale, fault-tolerant quantum computation,” says Dzurak.
“We’re now on the verge of a two-qubit accuracy that’s high enough for quantum error correction.”
These two sets of findings are key to constructing more feasible quantum computers, because greater accuracy means fewer redundant qubits are required for error correction.
“It shows it is possible to read out the state of a quantum bit in a silicon device using only a single wire (in this case a nanoscale electrode), vastly simplifying the on-chip electronics needed for a full-scale quantum processor chip,” explains Dzurak.
The fewer qubits required for processing problems, combined with reducing the size of read-outs required for each qubit enough, dramatically reduces the size and complexity of a quantum computer, thus bringing it that much closer to reality.
And industry has taken note.
The advances have made possible the scaling up of a system using silicon, based on industry-standard complementary metal-oxide-semiconductor (CMOS) transistors, in a joint venture between UNSW, Australian company Silicon Quantum Computing (SQC) and the CMOS chip manufacturing capabilities at the French technology agency CEA.
In using silicon for the quantum computing revolution, Australian researchers have shown that an old element can be taught new tricks.
Alan Duffy is an astrophysicist at Swinburne University of Technology, Melbourne. He was Lead Scientist of The Royal Institution of Australia from 2017 to 2021. Twitter | @astroduff
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