In the race to build the first functional quantum computer, Australian researchers at the University of NSW find coding possible in silicon

This article is more than 4 years old

This article is more than 4 years old

Australian researchers have demonstrated that a quantum version of computer code can be written on a silicon microchip with the highest level of accuracy ever recorded.

A quantum computer uses atoms rather than transistors as its processing unit, allowing it to conduct multiple complex calculations at once and at high speed. In the race to build the first functional quantum computer scientists around the world have been trying to write quantum code in a range of materials such as caesium, aluminium, niobium titanium nitride and diamond.

But researchers at the University of NSW have long been basing their research around silicon, because silicon is the building block of all modern electronic devices, which would make quantum code in a silicon microchip easier, more cost-effective and highly scalable.



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For the first time they managed to entangle a pair of quantum bits – units of quantum information also known as qubits – in silicon. Qubits allow computers to access code vastly richer than the digital codes used in normal computers which gives quantum computers their superior power.

By “entangling” the two qubits, in this case an electron and the nucleus of a single phosphorus atom, the researchers showed that the particles remained connected even when separated so that actions performed on one still affected the other.

“Qubits are physical objects that have two typical states, so imagine a spin that can point north or south, or a circuit where current can flow clockwise and counterclockwise, all binary possibilities,” Professor Andrea Morello, who led the research, said.

“But if you entangle the two of them together, you get a superposition of the different combinations of binary choice, so a spin can now point both north and south, and the current can flow clockwise and counter clockwise. Two binary things are occurring at the same time.”

This entanglement meant a quantum computing language or code vastly richer than standard digital codes used in normal computers could be accessed, with these special codes giving quantum computers their superior power, he said.

“You can think of it as having an additional vocabulary,” Morello, program manager at the Centre for Quantum Computation and Communication Technology, said.



“When you speak, you have 26 letters and a few hundred thousand words available to you. In a classical computer, the vocabulary is a combination of zeros and ones that constitute its code.

“In a quantum computer, imagine that you have the same zeros and ones, but because entanglement of quantum bits allow you to combine them in a way impossible on normal computers, it would be the equivalent of suddenly have a billion new words available to you using those same 26 letters.

“This is why quantum computing is so powerful.”

To mathematically prove the entanglement of the two particles had occurred, the finding had to past the Bells Test, a stringent and unforgiving test that detects even the most minor imperfection.

The research passed the test with the highest score ever recorded in an experiment. The findings were published in the international journal, Nature Nanotechnology, on Tuesday.

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Professor Andrew Dzurak, a silicon nanofabrication expert, said it demonstrated that silicon was a “fantastic” platform for quantum computing.

“We suspected that for some time, but this really clearly demonstrates it, and it also shows that these single-atom quantum bits can be very, very promising,” he said.

“In the area of silicon-based quantum computing, Australia is clearly in the lead, and is now a good two years ahead of our nearest competition in the field.”

Morello said currently there was a fairly limited understanding of what a functional quantum computer could do, since there was no prototype.

“It’s hard to invent a new algorithm without a computer to try it on,” he said.

But quantum computing’s greatest potential was perhaps in the field of medicine, he said.

“Wouldn’t you want a computer where you could tell it you had cancer and ask it what molecule to inject to kill it?” Morello said.

“The reason you can’t do that now is because even if you had full understanding of cancer cell killing you, there is no calculation that can answer that question, as it is a quantum problem. This is where quantum computing might have the biggest impact.”