Researchers gain electrical control of quantum bits

Researchers at the University of New South Wales are touting another breakthrough in quantum computing. They have encoded quantum information in silicon using simple electrical impulses.

It’s one of many advances the UNSW team has been working on over the past few years as they endeavour to bring the construction of affordable large-scale quantum computers a step closer to reality.

Associate professor, Andrea Morello from UNSW’s School of Engineering and Telecommunications, said his team had realised a new control method for future quantum computers.

The researchers demonstrated that a highly coherent qubit – like the spin of a phosphorous atom in isotopically-enriched silicon can be controlled using electric fields instead of using pulses of oscillating magnetic fields.

Professor Morello said the method works by distorting the shape of the electron cloud attached to the atom using a very localised electric field.

“This distortion at the atomic level has the effect of modifying the frequency at which the electron responds,” said Professor Morello.

“Therefore, we can selectively choose which qubit to operate. It’s a bit like selecting which radio station we tune to by turning a simple knob. Here, the knob is the voltage applied to a small electrode placed above the atom.”

UNSW said the key to the success of this electrical control method is the placement of qubits inside a thin layer of specifically purified silicon, containing only the silicon-28 isotope.

This isotope is perfectly non-magnetic and unlike those naturally occurring in silicon, does not disturb the quantum bit, Professor Morello said.

The findings suggest that it would be possible to locally control individual qubits with electric fields in a large-scale quantum computer using only inexpensive voltage generators rather than expensive high-frequency microwave sources, the researchers said.

This specific type of quantum bit can be manufactured using a similar technology to that employed for the production of everyday computers, reducing time and cost of development.

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