UNSW engineers have made a significant advance in quantum computing: they created 'quantum entangled states' - where two separate particles become so deeply linked they no longer behave independently - using the spins of two atomic nuclei. Such states of entanglement are the key resource that gives quantum computers their edge over conventional ones.
The research was published on Sept. 18 in the journal Science, and is an important step towards building large-scale quantum computers - one of the most exciting scientific and technological challenges of the 21st century.
Lead author Dr Holly Stemp says the achievement unlocks the potential to build the future microchips needed for quantum computing using existing technology and manufacturing processes.
"We succeeded in making the cleanest, most isolated quantum objects talk to each other, at the scale at which standard silicon electronic devices are currently fabricated," she says.
The challenge facing quantum computer engineers has been to balance two opposing needs: shielding the computing elements from external interference and noise, while still enabling them to interact to perform meaningful computations. This is why there are so many different types of hardware still in the race to be the first operating quantum computer: some are very good for performing fast operations, but suffer from noise; others are well shielded from noise, but difficult to operate and scale up.
The UNSW team has invested on a platform that - until today - could be placed in the second camp. They have used the nuclear spin of phosphorus atoms, implanted in a silicon chip, to encode quantum information.
"The spin of an atomic nucleus is the cleanest, most isolated quantum object one can find in the solid state," says Scientia Professor Andrea Morello, UNSW School of Electrical Engineering & Telecommunications.
"Over the last 15 years, our group has pioneered all the breakthroughs that made this technology a real contender in the quantum computing race. We already demonstrated that we could hold quantum information for over 30 seconds - an eternity, in the quantum world - and perform quantum logic operations with less than 1% errors.
"We were the first in the world to achieve this in a silicon device, but it all came at a price: the same isolation that makes atomic nuclei so clean, makes it hard to connect them together in a large-scale quantum processor."
Until now, the only way to operate multiple atomic nuclei was for them to be placed very close together inside a solid, and to be surrounded by one and the same electron.
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