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Wired Up: Majorana Fermions for Quantum Computing

Majorana fermions exhibit a strange property: these exotic particles cannot be distinguished from their own antiparticles. Nevertheless, technically they could be extremely useful as qubits for quantum computers. This is because every two Majorana fermions form an entangled pair that can be extremely resistant to external influences. However, Majorana fermions are very difficult to detect. This is a major hurdle for their production and characterization. Scientists from Forschungszentrum Jülich and RWTH Aachen University together with partners from the University of Hamburg can now demonstrate a possible way around this difficulty.

The researchers investigated quasiparticles at the ends of magnetic iron nanowires, which are considered to be possible Majorana fermions, using scanning tunnelling microscopy and computer simulations. Quasiparticles are excitation states consisting of several particles that behave like independent units when viewed from the outside. The excitation states at the ends of the nanowires are topologically protected, which makes them resilient to noise. If some of these turn out to be Majorana states, they could be used to ensure the integrity of qubits which would enable calculations to be performed correctly.

However, it was not certain whether the excitation states at the wire ends were actually Majorana states or – topologically not protected – so-called Yu-Shiba-Rusinov states. In order to differentiate between the two states, the researchers used a clever trick and extended the chains with non-magnetic cobalt atoms. This separated the spatial wire ends from the magnetic wire ends.

The atomic orbitals of the iron and cobalt regions of the wire, which form the basis for the excitation states, are similar so that even after elongation the electronic properties do not change drastically until the end of the wire. Nevertheless, the excitation states characteristic of the Majorana states did not migrate to the new end, but remained at the ends of the iron wires. The researchers regard this as a very probable indication that the Majorana states they are searching for are indeed at the ends of the iron wires. “If this is confirmed, we will be laying an essential foundation for the controlled production and manipulation of Majorana states,” says Prof. Samir Lounis from the Peter Grünberg Institute and the Institute for Advanced Simulation at Forschungszentrum Jülich.”

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