UNSW team creates single-atom transistor

UNSW team creates single-atom transistor

Research has implications for quantum computing

Australian researchers at the University of NSW's ARC Centre for Quantum Computation and Communication Technology have successfully created a single-atom transistor with implications for both classical and quantum computing.

The transistor uses a single phosphorous atom in a silicon crystal aligned with two electrodes that allow the researchers to pass a current through the device.

It's not the first time a single-atom transistor has been created; however, the precision which the team was able to achieve with their approach is new according to Professor Michelle Simmons, director of the ARC Centre for Quantum Computation and Communication Technology.

In the past people have created a "very small device and hope to isolate a single atom, or other people have tried to implant a single atom into a device and so there they really create the electrodes and everything first and fire an atom in".

However, the UNSW team was able "to put the atom in exactly where we want it and align the electrodes, so we can make it what we call a deterministic device with atomic precision."

A paper on the research was published in Nature Nanotechnology on 19 February.

The transistor could be used as a fundamental building block of a quantum computing: A qubit, roughly the equivalent of a bit in classical computing.

"What we've demonstrated here is the fundamental unit, and if you build a scalable system and you want to put lots of these qubits in place you need to control exactly the spacing at the atomic scale between the two atoms, and so you want to be able get them to interact and then you want to turn off the interactions controllably," Simmons said.

The ARC Centre for Quantum Computation and Communication Technology has started to work on constructing two- and three-atom devices.

"Ultimately you need tens to hundreds to make any kind of practical system and that's looking at least a decade away or more," Simmons said.

"If you look at a classical computer what it does is it looks at all the possible solutions to an answer and it looks at them one after another.

"So if you imagine you were to write a telephone number down on a piece of paper and you'd forgotten whose number it is, a classical computer would start in the phone directory at the As and go through all the As and then it would go through all the Bs and then it would go through the Cs. Eventually it would find the telephone number and tell you who it is.

In contrast, a quantum computer would look at all the possibilities at the same time.

"So you get this kind of exponential speed up in time of computation — and that's really the key difference between the two," Simmons said.

"It's this parallelism in the quantum world that you utilise."

Possible applications of quantum computation include super-fast database searching and encryption and decryption, as well as the simulation of quantum interactions.

American physicist Richard Feynman argued that one of the first applications of a quantum system or quantum computer would be to actually simulate the quantum world.

"So if you have a chemical reaction and you want to work out what the lowest energy state in a chemical reaction is, again because there are so many possibilities, you actually start to need quantum systems to be able to simulate quantum systems," Simmons said.

"Quantum simulation is going to allow us to understand the fundamentals of matter and interactions and how things form."

The research also has implications for non-quantum computing. Moore's Law, first observed by Intel co-founder Gordon Moore, says that the number of transistors that can be placed on a chip doubles roughly every 18-24 months.

"What the means is that the actual size of the smallest chip has to decrease at the same rate, and so you can actually plot out the size of the silicon transistor as a function of time," Simmons said.

"What we're showing here is that you can extend that all the way down to the level of a single atom.

"From the law at the moment it was predicted that would happen in about 2020 and what we've done is shown that we can make that single atom in silicon now."

Follow Rohan Pearce on Twitter: @rohan_p

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