Topological media can have a variety of exotic quantum states that are of interest for a whole range of applications. These include, in particular, Majorana modes, which have unique properties. These are fermionic particles or quasiparticles that are also their own antiparticles. In solid-state physics, Majorana zero modes that occur at the ends of one-dimensional topological superconductors are of interest. These states should exhibit non-trivial branching statistics. This makes such Majorana zero modes interesting for quantum information processing, as they could enable topologically protected data processing.
A research team involving the University of Copenhagen, the Microsoft Quantum Lab and Yale University has now demonstrated an interesting new way of producing nanowires with Majorana zero modes that can be addressed with comparatively low magnetic field strengths. The wires are also fully encased, which increases their longevity and is advantageous for potential applications in future quantum computers.
The researchers constructed their nanowires from a hexagonal semiconductor core of indium arsenide, which had a maximum diameter of 130 nanometers. This core was completely enclosed by a 30 nanometer thick aluminum shell. They produced the semiconductor core using molecular beam epitaxy on an indium arsenide substrate that was heated to 420 degrees Celsius. This made it possible to achieve lengths of up to around ten micrometers. The wire cores were then coated with aluminum by slowly rotating the substrate with the wires in front of an aluminum vapor source so that all six sides were evenly coated with aluminum. Subsequent measurements showed that Majorana modes occur even at moderate magnetic field strengths of 0.1 Tesla. This not only simplifies the integration of such wires into a quantum computing system, but also significantly increases the range of possible materials to work with. In addition, the nanowire is protected from unwanted contact with the environment by the solid coating. Further information can be found in the original publication:
S. Vaitiekėnas et al: Flux-induced topological superconductivity in full-shell nanowires, Science 367, eaav3392 (2020); DOI: 10.1126/science.aav3392 (Center for Quantum Devices, University of Copenhagen)
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