UNSW Australia

Quantum vision: Computing with a single electron in silicon

A research team led by Australian engineers has created the first working quantum bit based on a single atom in silicon, opening the way to ultra-powerful quantum computers of the future.

In a landmark paper published today in the journal Nature, the team describes how it was able to both read and write information using the spin, or magnetic orientation, of an electron bound to a single phosphorus atom embedded in a silicon chip.

“For the first time, we have demonstrated the ability to represent and manipulate data on the spin to form a quantum bit, or ‘qubit’, the basic unit of data for a quantum computer,” says Scientia Professor Andrew Dzurak. “This really is the key advance towards realising a silicon quantum computer based on single atoms.”

Dr Andrea Morello and Professor Dzurak from the UNSW School of Electrical Engineering and Telecommunications lead the team. It includes researchers from the University of Melbourne and University College, London.

“This is a remarkable scientific achievement – governing nature at its most fundamental level – and has profound implications for quantum computing,” says Dzurak.

Dr Morello says that quantum computers promise to solve complex problems that are currently impossible on even the world’s largest supercomputers: “These include data-intensive problems, such as cracking modern encryption codes, searching databases, and modelling biological molecules and drugs.”

The benefits of quantum computing

A functional quantum computer will provide much faster computation in three key areas: searching large databases, cracking most forms of modern encryption, and modelling atomic systems such as biological molecules and drugs. This means they’ll be enormously useful for finance and healthcare industries, and for government, security and defence organisations. Functional quantum computers will also open the door for new types of computational applications and solutions that are, at this stage, difficult to conceive or comprehend.

How quantum computers work

In current computing, information is represented by classical bits, which are always either a zero or a one – the equivalent to a transistor device being switched on or off. For quantum computing you need an equivalent: and in the UNSW design the data will be encoded on the spin – or magnetic orientation – of individual electrons, bound to single phosphorus atoms. These are known as quantum bits, or qubits.

A clockwise (or “up”) spin would represent a 1 and a counter-clockwise (or downward) spin would represent a 0 – but in the quantum realm, particles have a unique ability to exist in two different states at the same time, an effect known as quantum superposition. This gives rise to the unique ability envisioned for quantum computers to rapidly solve complex, data-intensive problems.

Multiple, coupled qubits can exist in states that have no classical analog, and they can be in many of such states at the same time. These special states are called “entangled states” because the information they contain tells you something about the correlations between the particles, but not the individual state of each particle. Using two qubits, the operation could be performed using four values, for three qubits on eight values, and so on. As you add more qubits, the capacity of the computers to perform operations increases exponentially. In fact, with just 300 qubits it is possible to store as many different numbers as there are atoms in the universe.

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