19-Nov-2015 - Universität Basel

Electrons Always Find a (Quantum) Way

Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel have demonstrated for the first time how electrons are transported from a superconductor through a quantum dot into a metal with normal conductivity. This transport process through a quantum dot had already been calculated theoretically in the nineties, but scientists at the University of Basel have now succeeded in proving the theory with measurements.

Transport properties such as electrical conductivity play an important role in technical applications of new materials and electronic components. Completely new phenomena occur, for example, when you combine a superconductor and nanometer-sized structures, known as quantum dots, in a component.

Researchers at the University of Basel working under Professor Christian Schönenberger have now constructed such a quantum dot between a superconductor and a metal with normal conductivity to study electron transport between the two components.

It should in fact be impossible to transport electrons from the superconductor through a quantum dot at low energies. Firstly, electrons never occur on an individual basis in a superconductor but rather always in two's or in so-called Cooper pairs, which can only be separated by relatively large amounts of energy. Secondly, the quantum dot is so small that only one particle is transported at a time due to the repulsive force between electrons.

In the past, however, scientists have repeatedly observed that a current nonetheless runs between the superconductor and the metal – in other words, electron transport does occur through the quantum dot.

First evidence of the transport mechanism through a quantum dot

On the basis of quantum mechanics, theories were developed in the nineties which indicated that the transport of Cooper pairs through a quantum dot is entirely possible under certain conditions. The prerequisite is that the second electron follows the first very quickly, namely within the time roughly stipulated by Heisenberg's uncertainty principle.

The scientists at the University of Basel have now been able to accurately measure this phenomenon. In their experiments the scientists found the exact same discrete resonances that had been calculated theoretically. In addition, the team including doctoral student Jörg Gramich and his supervisor Dr. Andreas Baumgartner was able to provide evidence that the process also works when energy is emitted into the environment or absorbed from it.

“Our results contribute to a better understanding of the transport properties of superconducting electronic nanostructures, which are of great interest for quantum technology applications”, says Dr. Andreas Baumgartner.

Facts, background information, dossiers
  • Universität Basel
  • quantum technology
More about Universität Basel
  • News

    Carbon-neutral “biofuel” from lakes

    Lakes store huge amounts of methane. In a new study, environmental scientists at the University of Basel offer suggestions for how it can be extracted and used as an energy source in the form of methanol. Discussion about the current climate crisis usually focuses on carbon dioxide (CO2). ... more

    New class of substances for redox reactions

    An interdisciplinary, multinational research team presents a new class of chemical compounds that can be reversibly oxidized and reduced. The compounds known as 'pyrazinacenes' are simple, stable compounds that consist of a series of connected nitrogen-containing carbon rings. They are suit ... more

    Kagome graphene promises exciting properties

    For the first time, physicists from the University of Basel have produced a graphene compound consisting of carbon atoms and a small number of nitrogen atoms in a regular grid of hexagons and triangles. This honeycomb-structured “kagome lattice” behaves as a semiconductor and may also have ... more

More about Swiss Nanoscience Institute
  • News

    New class of substances for redox reactions

    An interdisciplinary, multinational research team presents a new class of chemical compounds that can be reversibly oxidized and reduced. The compounds known as 'pyrazinacenes' are simple, stable compounds that consist of a series of connected nitrogen-containing carbon rings. They are suit ... more

    Real-time manipulation and control of nuclear spin noise

    Basel Physicists in collaboration with Dutch researchers have demonstrated a new method for polarizing nuclear spins in extremely small samples. By Monitoring and controlling spin fluctuations, the method may provide a route for enhancing the resolution of magnetic resonance imaging (MRI) o ... more