Skip to navigation | Skip to content

Silicon chip edges towards quantum memory

atom in silicon

The researchers use a silicon chip on this circuit board to demonstrate storage of quantum information (Source: Stephen Pincock)

Quantum memory It is possible to use phosphorous atoms in silicon to develop quantum memory, suggests new Australian research.

Associate Professor Andrea Morello and team from the University of New South Wales have demonstrated the ability to read and write information with 99 per cent accuracy or more on the nucleus of a single atom.

This level of accuracy rivals the current benchmark in quantum technology, which is not based on silicon, they report today in the journal Nature.

"[Our technology] can be wired up and operated electrically like normal integrated circuits," says Morello.

"Silicon is the dominant material in the microelectronics industry, which means [our technology] is more compatible with existing industry technology and is more easily scalable."

Storing quantum data

Quantum computers promise to solve problems currently unsolvable by conventional computers but to do so they will need to store as well as process quantum data.

Morello and colleagues have shown a phosphorous atom embedded in a silicon chip can be used to make a qubit -- the data processing unit of quantum computers -- capable of holding onto quantum information for a long time, providing the first steps towards true quantum memory.

Their technology involves using classical techniques to read and write quantum data onto parts of the atom by controlling and detecting change in spin.

The spin can be, for example up, or down, or in both states at the same time (quantum state).

Last year Morello and team reported, also in Nature, they could make a qubit by using the spin of an electron in such a phosphorous atom.

Now, they have made a working qubit by using the spin in the nucleus of the same phosphorous atom.

What's more is they have shown the nuclear spin qubit can store quantum information for longer than the electron spin qubit.

"We can use the most long lived one, which is the nucleus, as quantum memory, to store the state of the electron," says Morello, whose team is part of the Centre for Quantum Computation and Communication Technology.

"In you computer you have the RAM and you have the hard drive. The RAM is quick to access and do operations on, but then for long term you store your data on the hard drive," he adds. "You can think of it as the nucleus being the hard drive and the electron being the RAM."

He says the advantage in this case is the 'RAM' and 'hard drive' are naturally connected in the same atom so no wires are needed to connect them.

At present the nuclear spin qubit can hold memory for 60 milliseconds, but Morello is confident that with the use of purified silicon, the memory could last as long or longer than the benchmark.

The next step will be to demonstrate true quantum memory, which involves writing information on one electron, then copying that information onto the nucleus, leaving it there and then copying it back onto the electron.

'Beautiful demonstration'

Quantum physicist Associate Professor David Reilly of the University of Sydney says the findings are important.

"The result here is a beautiful demonstration of quantum memory and that's going to be a really enabling technology," says Reilly.

"Solid state semi-conductors are the most viable in terms of scalability," he adds. "It's exciting that it's in a material like silicon which is a semiconductor, a solid state material very similar to what's been used in regular computing."

Reilly says there are other contenders for quantum memory, for example qubits made of gallium arsenide, diamond, or even ion traps.

"I think at this stage it's very hard to tell which particular platform is going to really have legs to go the distance," says Reilly. "This is a very important breakthrough but I wouldn't stop working on a variety of other approaches."

The latest research was funded by the Australian Research Council and the US Army Research Office. The military is interested in funding quantum computing because it promises to improve data security.
