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Quantum superconducting nanowires

Various properties and phenomena that are unknown at our scale, appear instead at an atomic scale, opening the way for a new industrial revolution. Recent experiments performed on superconductors by Xavier Baumans, a PhD student at the University of Liège's Department of Physics, have established a limit beyond which nanowires permanently lose their superconductivity, even at very low temperatures. To achieve this, Xavier Baumans and his colleagues reduced the fabrication limit of these wires to the width of an atom! A major innovation, described in Nature Communications, which will undoubtedly interest quantum computer designers.

An assistant lecturer at the University of Liège's Physics Department (Materials Pole, Professor Alejandro Silhanek), Xavier Baumans studies the behaviour of extremely small superconducting electronic circuits. In this case, "extremely small" means from 100 nanometres (100 nm or 100 millionths of a metre) up to… a few atoms. These circuits are much sought after since they are involved in the composition of quantum computers. "Researchers already predicted then observed a strange phenomenon many years ago", Xavier Baumans explains. "If you reduce the size of devices too much, the superconductor effect can disappear!" In fact, a double phenomenon was observed: fluctuations of the order parameter (switching from superconductivity to no superconductivity) appear in two forms: thermal and quantum. As their name indicates, the latter aren't due to temperature but to size, owing to the fact that the scale is that of an atom. Therefore, we can't do anything about them because they are intrinsic to the system: even by reducing the temperature close to absolute zero, they are always present.

However, the observations made so far had limits. One relates to the size of the wires studied: approximately no more than 30 nm. Another concerns the fact that the observations were made according to several different samples: the researchers would take a 90 nm wire, then a 60 nm one and so on, and estimate a bracket where superconductivity disappeared.


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