Hardware
Cologne team sees predicted Andreev states in topological insulator Josephson junctions
Physicists at the University of Cologne, led by Professor Yoichi Ando, used tunneling spectroscopy on Josephson junctions built on a topological insulator and reported in Science Advances (published 30 October 2026). They observed highly transmissive Andreev states across a range of charge-carrier densities, and found the states concentrated in specific regions of the junction when a magnetic field was applied. The results agree with the 2008 model of Liang Fu and Charles Kane and with numerical simulations by Fabian Hassler's group at RWTH Aachen University. The team has not yet confirmed whether the states show the predicted closing and reopening of an energy gap, which could signal a transition to topological superconductivity.
Why it mattersTopological quantum computing aims to store information in states expected to resist local disturbances, and this work tests the theory of how superconductivity interacts with a topological insulator's surface. The researchers say the topological phase transition remains to be demonstrated, and that this needs better energy and time resolution in the experiment.