Quantum one-way street in topological insulator nanowires

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Applying a magnetic field causes current to flow more easily in one direction al

Applying a magnetic field causes current to flow more easily in one direction along the nanowire than in the opposite one. (Image: University of Basel, Department of Physics)

Very thin wires made of a topological insulator could enable highly stable qubits, the building blocks of future quantum computers. Scientists see a new result in topological insulator devices as an important step towards realizing the technology’s potential.

An international group of scientists have demonstrated that wires more than 100 times thinner than a human hair can act like a quantum one-way street for electrons when made of a peculiar material known as a topological insulator.

The discovery opens the pathway for new technological applications of devices made from topological insulators and demonstrates a significant step on the road to achieving so-called topological qubits, which it has been predicted can robustly encode information for a quantum computer.

To achieve this result, the groups of Jelena Klinovaja and Daniel Loss at the University of Basel closely collaborated with experimental physicists at the University of Cologne in the group of Yoichi Ando.

Insulator on the inside, conductor on the outside

Topological insulators are materials in which a combination of quantum mechanics and the mathematical concept of topology produce conductive surfaces and insulating interiors. Topological insulators are highly promising candidates for future technologies and as potential platforms for quantum computing.

The researchers were able to show that, under the right circumstances, electric currents can flow more easily in one direction compared to the other, a process known as rectification. Rectification offers a wide range of applications and forms the basis of most wireless technologies.

Rectifiers found in smartphones, for example, are now made of semiconductor diodes. However, the current rectification effect discovered in topological insulator nanowires arises as a result of quantum mechanics and is extremely controllable.

Usually, quantum rectification effects arise as a result of something known as spin-orbit coupling, which is a mix of quantum mechanics and Einstein’s theory of relativity. As one might expect, that strange mix normally results in tiny rectification effects.

"What’s great about the topological insulator nanowires is that we can artificially produce essentially the same physics but with a much larger magnitude," says Dr. Henry Legg, Georg H. Endress postdoctoral fellow at the University of Basel and first author of the paper. "This leads to a rectification effect that’s really huge compared to other materials. It’s also one of the aspects that makes topological insulators so exciting for applications in quantum computing."


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