UNSW obtains 10-fold boost in quantum computing stability

A team of engineers at the University of New South Wales has expanded the time during which calculations could be performed in a future silicon quantum computer.
Written by Asha Barbaschow, Contributor

Engineers at the University of New South Wales (UNSW) have created a new quantum bit (qubit) which remains in a stable superposition for 10 times longer than previously achieved, expanding the time during which calculations could be performed in a future silicon quantum computer.

According to Arne Laucht, a Research Fellow at the School of Electrical Engineering & Telecommunications at UNSW, the new qubit, made up of the spin of a single atom in silicon and merged with an electromagnetic field -- known as a dressed qubit -- retains quantum information for much longer that an "undressed" atom, which opens up new avenues quantum computer creation.

The Australian-based team said the race to building a quantum computer has been called the "space race of the 21st century" as it is both a difficult and ambitious challenge to undertake.

The appeal, however, is the potential to deliver revolutionary tools for tackling otherwise impossible calculations, such as the design of complex drugs and advanced materials, or the rapid search of large-scale, unsorted databases.

Explaining the importance of the breakthrough, Andrea Morello, leader of the research team and a program manager in the Centre for Quantum Computation & Communication Technology (CQC2T) at UNSW, said its speed and power lies in the fact that quantum systems can host multiple "superpositions" of different initial states, treated as inputs in a computer that all get processed at the same time.

"The greatest hurdle in using quantum objects for computing is to preserve their delicate superpositions long enough to allow us to perform useful calculations," he said.

"Our decade-long research program had already established the most long-lived quantum bit in the solid state, by encoding quantum information in the spin of a single phosphorus atom inside a silicon chip, placed in a static magnetic field."

What Laucht and his colleagues did was push this further, implementing a new way to encode the information.

"We have subjected the atom to a very strong, continuously oscillating electromagnetic field at microwave frequencies, and thus we have 'redefined' the quantum bit as the orientation of the spin with respect to the microwave field," he said.

UNSW explained that as the electromagnetic field steadily oscillates at a very high frequency, any noise or disturbance at a different frequency results in a zero net effect. The work undertaken by the university team achieved an improvement by a factor of 10 in the time span during which a quantum superposition can be preserved.

"This new dressed qubit can be controlled in a variety of ways that would be impractical with an undressed qubit. For example, it can be controlled by simply modulating the frequency of the microwave field, just like in an FM radio. The undressed qubit instead requires turning the amplitude of the control fields on and off, like an AM radio," Morello added.

"In some sense, this is why the dressed qubit is more immune to noise: the quantum information is controlled by the frequency, which is rock-solid, whereas the amplitude can be more easily affected by external noise".

Last week, Morello was named inaugural recipient of the Rolf Landauer and Charles H. Bennett Award in Quantum Computing by the US-based organisation of physicists, the American Physical Society, for his "remarkable achievements in the experimental development of spin qubits in silicon".

Another team of UNSW engineers announced in October last year they had built a quantum logic gate in silicon, which made calculations between two qubits of information possible.

At the time, the discovery was called a landmark result not only for Australia, but for the world, as until then it had not been possible to make two quantum bits "talk" to each other and create a logic gate using silicon.

"This result means that all of the fundamental building blocks that are required to make a full scale silicon processor chip are now in place," Andrew Dzurak, scientia professor at the university, said previously. "We're ready to move from this scientific research phase, into the engineering stage and the manufacturing stage."

Building on this breakthrough, another team of researchers out of the university, led by professor Michelle Simmons, unlocked the key to enabling quantum computer coding in silicon, announcing in November that the team had the capability to write and manipulate a quantum version of computer code using two qubits in a silicon microchip.

UNSW officially opened the new CQC2T laboratory complex in April, which will eventually house six new scanning tunnelling microscopes that can be used to precisely position individual atoms within silicon.

Following the advancements UNSW has achieved in quantum computing, the federal government allocated AU$26 million of its AU$500 million science funding to support its work in quantum computing.

The science funding forms part of Australia's AU$1.1 billion National Innovation and Science Agenda that was unveiled in December.

Within 48 hours of the cash injection from the federal government, the Commonwealth Bank of Australia pledged AU$10 million over five years to support the university's researchers. Telstra then matched CommBank's efforts, also pledging AU$10 million over five years, to boost UNSW's capacity to develop the world's first silicon-based quantum computer.

According to the university, it is the only research group in the world that can make atomically precise devices in silicon.

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