Affordable quantum computers with electrical control method

Chuck Bednar for – @BednarChuck

By using simply electrical pulses to encode quantum information in silicon for the first time, a team of researchers from the University of New South Wales has brought use one-step closer to having affordable, large scale quantum computing technology.

Writing in the open-access journal Science Advances, Andrea Morello, an assistant professor in the UNSW School of Electrical Engineering and Telecommunication, and his colleagues report how they were able to use this to create a new control method for quantum computers.

Finding a faster, cheaper way to produce quibits

While traditional computers store data on transistors and hard drives, quantum computers encode that information in the quantum states of microscopic objects known as qubits, the authors report in their study. The new technique works by distorting the shape of the electron cloud attached to the atom, using a very localized electric field, Morello explained.

“This distortion at the atomic level has the effect of modifying the frequency at which the electron responds,” the professor explained in a statement. “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 could be possible to locally control individual qubits using electric fields in a large-scale quantum computer without the need for costly high-frequency microwave sources. It uses only inexpensive voltage generators, and this specific type of qubit can be made using a faster, cheaper method similar to those used to make traditional computers.

Building upon previous research at the university

The device used in the experiment, which was fabricated at the UNSW node of the Australian National Fabrication Facility, focuses on the placement of the quibits inside a thin layer of specially purified silicon that contains only the silicon-28 isotope. That isotope is perfectly non-magnetic and does not disturb the quantum bit whatsoever, Morello said.

The research builds upon previous work in the field conducted at the university, which starting in 2012 became the first research facility to demonstrate single-atom spin qubits in silicon. Morello and his colleagues has already improved the control of those qubits to 99 percent accuracy, and last year set a new record for how long quantum information can be stored in the solid state.

“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,” added UNSW post-doctoral researcher, Dr. Arne Laucht.


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