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Cost of Quantum Computer Qubit Control Cut

Quantum information has been encoded in silicon using simple electrical pulses for the first time, bringing the construction of affordable large-scale quantum computers one step closer to reality.

Unlike conventional computers that store data on transistors and hard drives, quantum computers encode data in the quantum states of microscopic objects called qubits. A/Prof Andrea Morello of the University of NSW said the new research, which has been published in Science Advances, had successfully realised a new control method for future quantum computers.

“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 the lead author of the study, Dr Arne Laucht of The University of NSW.

Morello said the method uses a very localised electric field to distort the shape of the electron cloud attached to the atom. “This distortion at the atomic level has the effect of modifying the frequency at which the electron responds. 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,” Morello said. “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 expensive high-frequency microwave sources.

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

The key to the success of the electrical control method is the placement of the qubits inside a thin layer of 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.