This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: One approach to making information storage in quantum computing less prone to errors is known as topological quantum computing. It relies on special quantum states that are expected to be more resistant to local disturbances.
Physicists at the University of Cologne have now observed quantum states that behave as predicted in a material system considered promising for this approach. Their findings, published under the title "Tunneling spectroscopy of topological insulator Josephson junctions" in Science Advances, support a theoretical description of how superconductivity interacts with the surface of a topological insulator. Topological insulators are materials that do not conduct electricity in their interior but conduct it along their surfaces.
When combined with a conventional superconductor, their surface states are predicted to support a special form of superconductivity known as topological superconductivity. If realized, this could provide a route to Majorana zero modes, quantum states being investigated for their potential use in topological quantum bits, or qubits. Demonstrating and controlling these states experimentally remains a challenge.
To investigate the predicted behavior, Dr. Jakob Schluck, Ella Nikodem (M.Sc.) and colleagues in the Topological Matter Laboratory Cologne, led by professor Yoichi Ando, studied a structure called a Josephson junction. It consists of two superconductors connected by a nonsuperconducting region.
Using tunneling spectroscopy, the researchers probed the quantum states inside the junction while varying the phase difference between the two superconductors. The team observed highly transmissive Andreev states, which form when electrons and holes interact at a superconducting junction. The states appeared across a range of charge-carrier densities, consistent with the predicted behavior of electrons at the topological insulator's surface.
When the researchers applied a magnetic field, they also found these states concentrated in specific regions of the junction, as theory predicts. "Understanding how superconductivity interacts with the distinctive electronic properties of topological insulators is essential for assessing their potential for topological quantum computing," says Ando. The experimental results agree with theoretical predictions based on the model proposed by Liang Fu and Charles Kane in 2008, as well as numerical simulations carried out by the group of professor Fabian Hassler at RWTH Aachen University.
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