Towards Silicon-Based Quantum Computers

The ability to control a single 31P atom in silicon paves the way for a feasible quantum computer.

AsianScientist (Apr. 13, 2015) – A team of researchers has succeeded in encoding quantum information in silicon for the first time, bringing the construction of affordable large-scale quantum computers one step closer to reality. Their findings have been published in Science Advances.

Unlike conventional computers that store data on transistors and hard drives, quantum computers encode data in the quantum states of microscopic objects called qubits.

Researchers have already improved the control of these qubits to an accuracy of above 99 percent and established the world record for how long quantum information can be stored in the solid state, as published in Nature Nanotechnology in 2014.

In the present study, the same team of researchers has now demonstrated a key step that had remained elusive since 1998.

“We demonstrated that a highly coherent qubit, like the spin of a single phosphorus atom in isotopically enriched silicon, can be controlled using electric fields, instead of using pulses of oscillating magnetic fields,” explained Dr. Arne Laucht, post-doctoral researcher at the University of New South Wales and co-author of the study.

Team leader Associate Professor Andrea Morello said the method works by distorting the shape of the electron cloud attached to the atom, using a very localized electric field:

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

“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.”

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 the expensive high-frequency microwave sources.

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

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

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

The article can be found at: Laucht et al. (2015) Electrically Controlling Single-spin Qubits In A Continuous Microwave Field.

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Source: The University of New South Wales.
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