Large quantum computers closer to reality

Scientists have for the first time encoded quantum information using simple electrical pulses, bringing 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.
The University of New South Wales (UNSW) team was first in the world to demonstrate single-atom spin qubits in silicon.
The team has already improved the control of these qubits to an accuracy of above 99 per cent and established the world record for how long quantum information can be stored in the solid state.

It 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," said UNSW's Dr Arne Laucht, post-doctoral researcher and lead author of the study.

UNSW Associate Professor Andrea 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.

"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," said Morello.
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.

The finding was published in the journal Science Advances.