Researchers at the University of Twente and Utrecht University demonstrated for the first time that quantum states in the ultra-narrow material germanene can be switched on and off using only an electric field. The researchers were able to vary the electric field strength very precisely, causing the special 'topological' states in nanoribbons to disappear or appear.
Quantum computers will not use zeros and ones, but instead use quantum bits that can assume both states simultaneously. In theory, this makes them superfast and powerful, but in practice, building quantum bits is an enormous challenge: they are very sensitive to noise and quickly lose their information.
Graphene’s little brother: germanene
Researchers are therefore looking for materials that are stable enough to protect the fragile quantum states. Researchers at Utrecht University and the University of Twente have shown that ultra-narrow strips of the material germanene could be promising.
Germanene resembles the well-known material graphene in shape. It consists of a single layer of germanium atoms in a slightly wavy pattern. In extremely narrow ribbons (2–4 hexagons wide), so-called zero-dimensional topological states arise at the ends. These are interesting as building blocks for stable quantum bits because they are naturally more resistant to noise than normal quantum states.
Switching quantum states on and off
This new research shows for the first time that you can switch between these states using a local electric field. "We can bring these topological end states under complete electrical control," says Esra van 't Westende of the University of Twente, co-author of the publication. "By changing the distance between the scanning tunnelling microscope and the nanoribbon, we adjust the local electric field. This allows us to literally switch the quantum state on or off."
At low fields, the extremely narrow nanoribbons show a clearly measurable end state. If the field becomes stronger, this state disappears completely. With wider ribbons, the opposite happens: at higher electric fields, they suddenly do exhibit topological end states. Modelling by the Utrecht University theory team (Lumen Eek and Cristiane Morais Smith) revealed how the electric field triggers the switching, and predicted that narrower and wider ribbons behave differently.
Research into new quantum materials
The research is part of the national QuMat programme, in which Dutch universities collaborate on new materials for quantum technology. The collaboration between the UT and the UU was intensive. "This project shows exactly why we have QuMat: experimental and theoretical groups working together to design new materials for future quantum devices," says Dr Pantelis Bampoulis of the University of Twente.
Esra D. van ’t Westende is a PhD researcher in the Physics of Interfaces and Nanomaterials (PIN) group (Faculty of Science and Technology / MESA+) at the University of Twente, supervised by Dr Pantelis Bampoulis. The research, entitled 'Electric-Field Control of Zero-Dimensional Topological States in Ultranarrow Germanene Nanoribbons', was recently published in the scientific journal Physical Review Letters.
DOI: 10.1103/jx2x-fb5b
