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Tying qubits in knots

Photo of a knot

By Hamish Johnston at the AAAS Annual Meeting, Vancouver, Canada

Some of the world’s leading experts on quantum computing are here in Vancouver for the American Association for the Advancement of Science (AAAS) annual meeting – and it’s been great to hear them speak and to also interview some of them.

One topic that has come up several times is the idea of topological quantum computing. A major challenge for those trying to build practical quantum computers is how to protect the “quantumness” of their fragile devices from the destructive effects of environmental noise and heat.

One approach is to take advantage of the topological nature of some quantum states. One example involves quasiparticles called anyons that are predicted to exist in 2D semiconductors. One feature of anyons is that they cannot overlap with each other as they travel through space and time. The result is that the anyons exist in quantum states called “braids” that criss-cross each other.

A key feature of the braids is that they are robust to noise and heat. Indeed, to destroy such a state it must be unravelled much like untying a knot – a process that takes time and effort. This is unlike a more conventional quantum state such as the spin of an electron, which can be destroyed by a simple nudge from a random magnetic field.

Michael Freedman of Microsoft Station Q in Santa Barbara is one of the pioneers in developing the theory of topological computing, and he spoke at the conference. He left the audience with this vision for the future: “There is a serious prospect that quantum computing will change the face of computation.”

Other speakers had a complementary take on this. Scott Aaronson of the Massachusetts Institute of Technology believes that quantum computing and the emergence of quantum computers will give physicists new insights into quantum physics. “Quantum computing has opened a two-way street between physics and the science of computation,” he said.

The essential guide to topological computing can, of course, be found in Physics World.

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