Australian researchers have created the most accurate quantum computing technology to date
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Artist impression of an electron wave function (blue), confined in a crystal of silicon-28 atoms (black), controlled by a nanofabricated metal gate (silver).
Image: Dr Stephanie Simmons/UNSW

Researchers from the University of New South Wales (UNSW) in Australia have achieved a huge breakthrough in quantum computing - they’ve created two kinds of silicon quantum bit, or qubits, the building blocks that make up any quantum computer, that are more than 99 percent accurate.

These quantum bits are made from silicon, the same material that makes up the transistors in today’s computers and phones, but the information in these bits is processed and stored in atoms, which means they’re capable of storing exponentially more information. In fact, if scientists can reliably create a functioning quantum computer out of these quantum bits, it has the potential to be millions of times more powerful than today’s most powerful supercomputers.

"For quantum computing to become a reality we need to operate the bits with very low error rates," said Andrew Dzurak, the director of the Australian National Fabrication Facility at UNSW, where the devices were made, in a press release.

Now the teams from UNSW have managed to create not just one, but two quantum bits with more 99 percent accuracy, and their results have been published simultaneously in Nature Nanotechnology (here and here).

“We have demonstrated that with silicon qubit we can have the accuracy needed to build a real quantum computer," Dzurak told ABC Science. "That's the first time this has been done in silicon.”

The interesting thing is that the two groups, who both work in the same laboratories, used different approaches to come to the same result - one team embedded a phosphorous atom into the silicon, and the other, led by Dzurak, embedded an artificial atom.

"We've now come up with two parallel pathways for building a quantum computer in silicon, each of which shows this super accuracy,” said Andrea Morello from the UNSW School of Electrical Engineering and Telecommunications, who led the phosphorous atom team, in the press release.

Morello’s team based their advances on previous research on phosphorous atom quantum bits. Prior to this, the team had only managed to achieve around 50 percent accuracy with these chips, but by purifying the silicon that the atoms were embedded in, they have now achieved an incredible 99.99 percent accuracy.

The postdoctoral researcher who was lead author on Morello’s paper explained in the press release: “The phosphorus atom contains in fact two qubits: the electron, and the nucleus. With the nucleus in particular, we have achieved accuracy close to 99.99 percent. That means only one error for every 10,000 quantum operations.”

Dzurak’s team was able to create an “artificial atom” quantum bit that’s remarkably similar to the transistors used in commercial electronics. Today’s transistors work by turning on or off a flow of electrons, resulting in binary zeros and ones. In Dzurak’s quantum bit, this transistor has just one electron trapped inside, which can be on, off or in a superposition.

"This lets us use exactly the same sort of transistor that we use in computer chips and operate it as a qubit, opening the potential to mass-produce this technology using the same sort of equipment used for chip manufacturing,” Dzurak told ABC Science.

Both the breakthroughs were achieved by embedding the atoms in a thin layer of specially purified silicon, which contains only the silicon-28 isotope. Naturally occurring silicon is magnetic and therefore disturbs the quantum bit, messing with the accuracy of its data processing, but silicon-28 is perfectly non-magnetic.

The teams were also able to set a new record for how long a silicon quantum system retains information, known as coherence time.

“Coherence time is a measure of how long you can preserve quantum information before it’s lost," said Morello in the press release. And the longer coherence time, the easier it is for computers to perform complex calculations.

The researchers were able to store quantum information in the phosphorous nucleus for 35 seconds - something unheard of in quantum computing.

"Half a minute is an eternity in the quantum world. Preserving a ‘quantum superposition’ for such a long time, and inside what is basically a modified version of a normal transistor, is something that almost nobody believed possible until today," said Morello.

The research teams are now working together to take the best elements from each system to make a superior quantum bit. They’re hoping it will be the model that will be used to finally create the real quantum computers the world’s been waiting for.

“For our two groups to simultaneously obtain these dramatic results with two quite different systems is very special, in particular because we are really great mates,” said Dzurack in the press release. Aw, we love collaboration.

Find out more about the breakthrough in the video below:

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Sources: UNSW, ABC Science