A team from the University of Sydney and Microsoft, with Stanford University in the U.S., has miniaturized a component that is essential for the scale-up of quantum computing. The work constitutes the first practical application of a new phase of matter, called topological insulators, that was discovered in 2006.
Other than the familiar phases of matter — solid, liquid or gas — topological insulators are materials that operate as insulators in the bulk of their structures but have surfaces that act as conductors. Manipulation of these materials provides a pathway to construct the circuitry needed for interaction between quantum and classical systems, which is vital for building a practical quantum computer.
The Sydney team’s component, coined a microwave circulator, acts like a traffic roundabout, ensuring that the electrical signals only propagate in one direction, clockwise or anticlockwise, as required. Similar devices are found in mobile phone base-stations and radar systems and will be required in large quantities in the construction of quantum computers. A major limitation, until now, is that typical circulators are bulky objects the size of a human hand.
The invention represents the miniaturization of the common circulator device by a factor of 1,000. This has been done by exploiting the properties of topological insulators to slow the speed of light in the material. This miniaturization paves the way for many circulators to be integrated on a chip and manufactured in the large quantities that will be needed to build quantum computers.
Professor David Reilly, the leader of the Sydney team, said: “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. Even if we had millions of qubits today, it is not clear that we have the classical technology to control them. Realizing the scaled-up quantum computer will require the invention of new devices and techniques at the quantum-classical interface."
Alice Mahoney, Ph.D. candidate and lead author of the paper said: “Such compact circulators could be implemented in a variety of quantum hardware platforms, irrespective of the particular quantum system used."
A practical quantum computer is still some years away. Scientists expect to be able to carry out currently unsolvable computations with quantum computers that will have applications in fields such as chemistry and drug design, climate and economic modeling and cryptography.
The paper on this research was published in Nature Communications.