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Scientists claim breakthrough in quest for new quantum computer

Scientists have taken a "game changing" leap towards building practical quantum computers that could revolutionise the digital world.

The Australian team has paved the way for production of the first quantum computing "chips" by building a logic gate using the new technology based on silicon.

Logic gates are the fundamental building blocks of computer circuits - the logically controlled "switches" that allow calculations to be made.

The new device exploits a weird property of quantum physics that allows sub-atomic particles to exist in more than one state at the same time.

Problem-solving machines that employ quantum "qubits" rather than classical "bits" of information have the potential to find solutions that are far beyond the reach of even the most powerful of today's super-computers.

Professor Andrew Dzurak, Scientia, from the Australian National Fabrication Facility at the University of New South Wales, said: "We've demonstrated a two-qubit logic gate - the central building block of a quantum computer - and, significantly, done it in silicon.

"Because we use essentially the same device technology as existing computer chips, we believe it will be much easier to manufacture a full-scale processor chip than for any of the leading designs, which rely on more exotic technologies.

"This makes the building of a quantum computer much more feasible, since it is based on the same manufacturing technology as today's computer industry."

In the kind of classical computer circuit we are all familiar with data is presented in one of two states, represented as zero or one.

But a quantum bit, or "qubit", can exist in a "superposition" of both these states at once, allowing many computations to be performed in parallel.

On a physical level, bits are typically stored on a pair of silicon transistors, one of which is switched on while the other is off.

In the quantum computer data is encoded in the "spin", or magnetic orientation, of individual electrons. Not only can they be in one of two "up" or "down" spin states, but also a superposition of up and down.

The key step taken by the Australian scientists was to reconfigure traditional transistors so that they can work with qubits instead of bits.

Lead author Dr Menno Veldhorst, also from the University of New South Wales, said: " The silicon chip in your smartphone or tablet already has around one billion transistors on it, with each transistor less than 100 billionths of a metre in size.

"We've morphed those silicon transistors into quantum bits by ensuring that each has only one electron associated with it. We then store the binary code of 0 or 1 on the 'spin' of the electron, which is associated with the electron's tiny magnetic field."

The team, whose research is reported in the journal Nature, has taken out a patent on a full-scale quantum computer chip that could perform functions involving millions of qubits.

A practical quantum chip could have a huge impact in areas where classical computers face an uphill struggle.

These include weather forecasting, the stock market, drug development, code-breaking and encryption, and exploring the fundamental nature of the universe.

A logic gate acts like a doorman who is instructed to allow people into a night club only if they obey certain rules.

For instance, one common type of gate enforces the electronic equivalent of a rule that says "everyone in your group must wear a tie". If only one of two people arriving at the door of the club is wearing a tie, neither will be permitted entry.

In a similar way, if one of a logic gate's two inputs is "on" and the other "off" the output will be zero. A "1" output is only possible if both inputs are "on".

This is known as an "AND" gate. Other kinds of logic gate have different rules.

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