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Alice Mahoney, PhD candidate and lead author of the University of Sydney's recent paper on topological insulators, works on quantum science at the Sydney Nanoscience Hub. Image credit: University of Sydney

Major electronics companies are jockeying to be the first to hit “quantum supremacy,” the point at which a quantum computer can perform beyond what is possible on any conventional computer. On Nov. 10, IBM announced a commercialized computer that can run 50 quantum bits, enabling it to simulate very complex problems.

As the New York Times points out, Microsoft, Google, and Intel as well as a company owned by three Yale professors, Quantum Circuits, are all working on a quantum computer that can be used by consumers. Current versions are still too difficult to use for most people who aren’t the physicists who work on them.

Researchers at the University of Sydney, in a partnership with Microsoft and Stanford University, are attempting to get ahead of the game by miniaturizing a component that could be used in commercial quantum computers, a topological insulator.

In order to understand how it works, one needs to cover the basics of quantum computing. While traditional computers use bits that flip from one to zero to store information, quantum bits (“qubits”) can store four values at once.

"It is not just about qubits, the fundamental building blocks for quantum machines. Building a large-scale quantum computer will also need a revolution in classical computing and device engineering," said David Reilly, a professor at the University of Sydney.

"Even if we had millions of qubits today, it is not clear that we have the classical technology to control them. Realizing a scaled-up quantum computer will require the invention of new devices and techniques at the quantum-classical interface."

The University of Sydney team is working on topological insulators, types of matter which are constructed at the structural level such that they serve as insulators on the inside but have surfaces which are conductors. They can be used to create an interface between quantum computing and traditional computing systems.

These can be used in microwave circulators, the component on which the Sydney team worked. The team successfully miniaturized this component, which directs electrical signals to propagate in either clockwise or anti-clockwise directions, by a factor of 1000. Previous versions of this type of microwave circulator had to be large, about the size of a human hand. In order to miniaturize their version, the University of Sydney researchers slowed the speed at which the electrons travel inside the material by leveraging the particular properties of topological insulators. (A more in-depth explanation of this can be found at IEEE here.)

"Such compact circulators could be implemented in a variety of quantum hardware platforms, irrespective of the particular quantum system used,” said Alice Mahoney, lead author of the paper.

The smaller microwave circulators don’t solve every problem preventing quantum computing from going mainstream. Some researchers, including Professor Gil Kalai of the Hebrew University of Jerusalem, believe that current understanding of the quantum states themselves is not sufficient to engineer quantum computers. Is quantum computing a pie-in-the-sky idea, an effort to reach toward an “impossible machine” able to surpass even today’s supercomputers? Robert Schoelkopf and colleagues at Quantum Circuits have been working for decades on workable qubits and told the New York Times that researchers can likely improve “coherence time,” which makes calculations more precise, by a factor of 10 every three years.

Either way, Sydney and Microsoft, which collaborate on the university’s Microsoft Quantum Laboratory, have poured millions of dollars into making sure that it’s Bill Gates’ brainchild that commercializes a quantum computer. They’re doing well so far: the theoretical work that led to the invention of the topological insulator state of matter received the Nobel Prize for Physics in 2016.

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