by Byron Connolly

Scientists demonstrate key component of quantum machine

Apr 18, 20134 mins
Technology Industry

Mass production of incredibly powerful quantum computers may be only 10 years away thanks to researchers at the University of New South Wales who have demonstrated a quantum bit based on the nucleus of a single atom in silicon.

The breakthrough is a significant step forward from the creation of the world’s first quantum bit in September last year.

UNSW professor Andrew Dzurak said last year, researchers wrote and read back quantum information on an electron that was bound to an atom.

“This year, we have drilled down inside the atom, writing and reading information on the nucleus of an atom, which is a million times smaller,” Dzurak said. “When we work with the nucleus, we have a more accurate quantum bit than we had in September last year.

“The previous quantum bit, although demonstrated, didn’t have the accuracy necessary to do reliable calculations; no we have a quantum bit that can do that.”

Dzurak said having more accurate quantum bits will enable scientists to “scale up” and make more viable quantum machines.

“We have moved to a more advanced level [in quantum computing], with a [quantum bit] that is hundreds of thousands of times more accurate than previously,” he said. “We achieved a read-out fidelity of 99.8 per cent, which sets a new benchmark for qubit accuracy in solid state devices.”

Dzurak said that quantum technology can be manufactured now, but commercial quantum-based machines are still 10 years away.

He compared the cycle of quantum computer development to the discovery of the first transistor in a silicon chip – which was first demonstrated in 1947 – and how it took “a couple of decades” before integrated circuits and modern computers were created.

He says developing one quantum computer to hundreds of thousands takes a “significant engineering life span.”

Quantum bits, or qubits, are the building blocks of quantum computers and offer enormous advantages for searching databases, breaking modern encryption and modelling “atomic-scale” systems such as biological molecules and drugs. These qubits are coupled together to create massive increases in computing power.

The new quantum process

The new discovery was published on Thursday in Nature and describes how information is stored and retrieved using the magnetic spin of a nucleus.

“We have adapted magnetic resonance technology, commonly known for its application in chemical analysis and MRI scans, to control and read-out the nuclear spin of a single atom in real-time,” said UNSW associate professor Andrea Morello.

According to the researchers, the nucleus of a phosphorus atom is an extremely weak magnet, which can point in two natural directions, either “up or down.” In the quantum world, the magnet can exist in both states simulatenously – a feature known as “quantum superposition.”

These natural positions are equivalent to the “zero and “one” of a binary code, as used in existing classical computers, UNSW scientists said. In this experiment, the scientists controlled the direction of the nucleus, “writing” a value onto its spin and then “reading” that value out – turning the nucleus into a functioning qubit.

The accuracy of this qubit rivals what many consider to be today’s best quantum bit – a single atom in an electromagnetic trap inside a vacuum chamber, the researchers said.

“Our nuclear spin qubit operates at a similar level of accuracy but it’s not in a vacuum cleaner – it’s in a silicon chip and can be wired up and operated electrically like normal integrated circuits,” said Morello.

“Silicon is the dominant material in the microelectronics industry, which means our qubit is more compatible with existing industry technology and is more easily scalable.”

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