Sole Electron Reader Opens Path for Quantum Computation

A team led by engineers and physicists at the University of New South Wales (UNSW) in Sydney, Australia, make developed one of the key building blocks needed to make a quantum computer using silicon: a "single electron reader."
Artist's impression of a phosphorus atom (red sphere surrounded by a blue electron cloud, with spin) coupled to a silicon single-electron transistor, to achieve single-shot readout of the phosphorus electron spin. (Credit: William Algar-Chuklin, College of Fine Arts, The University of New South Wales)

Their work was published in the journal Nature.

Quantum computers promise exponential function increases in processing speed over today's computers through their use of the "spin," or magnetic orientation, of single electrons to correspond data in their computings.

In order to employ electron spin, the quantum computer needs both a way of changing the spin state (write) and of measuring that change (read) to form a qubit -- the equivalent of the bits in a conventional computer.

In creating the single electron reader, a team of engineers and physicists led by Dr Andrea Morello and Professor Andrew Dzurak, of the School of Electrical Engineering and Telecommunications at UNSW, has for the first time made possible the measurement of the spin of one electron in silicon in a single shot experiment. The team also includes researchers from the University of Melbourne and Aalto University in Finland.

"Our device detects the spin state of a single electron in a single phosphorus atom implanted in a block of silicon. The spin state of the electron controls the flow of electrons in a nearby circuit," said Dr Morello, the lead author of the paper, Single-shot readout of an electron spin in silicon.

"Until this experiment, no-one had actually measured the spin of a single electron in silicon in a single-shot experiment."

By using silicon -- the foundation material of conventional computers -- rather than light or the esoteric materials and approaches being pursued by other researchers, the device opens the way to constructing a simpler quantum computer, scalable and amenable to mass-production.

The team has built on a body of research that has put Australia at forefront of the race to construct a working quantum computer. In 1998 Bruce Kane, then at UNSW, outlined in Nature the concept for a silicon-based quantum computer, in which the qubits are defined by single phosphorus atoms in an otherwise ultra-pure silicon chip. The new device brings his vision closer.

"We expect quantum computers will be able to perform certain tasks much faster than normal computers, such as searching databases, modelling complex molecules or developing new drugs," says co-author Prof Andrew Dzurak. "They could also crack most modern forms of encryption."

"After a decade of work trying to build this type of single atom qubit device, this is a very special moment."

Now the team has created a single electron reader, they are working to quickly complete a single electron writer and combine the two. Then they will combine pairs of these devices to create a 2-bit logic gate -- the basic processing unit of a quantum computer.

The research team is part of the Australian Research Council (ARC) Centre of Excellence for Quantum Computer Technology, which is headquartered at UNSW. The team is led by Professor Dzurak and Dr Morello, with Mr Jarryd Pla and Dr Floris Zwanenburg as key supporting experimentalists. The paper's co-authors include Prof David Jamieson from the University of Melbourne; Dr Bob Clark, Australia's Chief Defence Scientist, and 10 other researchers from UNSW, The University of Melbourne, and Finland's Aalto University.

The research was funded by: the Australian, US, and NSW governments; UNSW; and the University of Melbourne.

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