Combining two ultra-thin material layers yields new possibilities for quantum electronics. A research team with members from TU Wien presents strongly tunable quantum systems.
Two novel materials, each composed of a single atomic layer and the tip of a scanning tunneling microscope - these are the ingredients to create a novel kind of a so-called "quantum dot". These extremely small nanostructures allow delicate control of individual electrons by fine-tuning their energy levels directly. Such devices are key for modern quantum technologies.
These are new kinds of quantum bits: extremely small nanostructures allow delicate control of individual electrons by fine-tuning their energy levels.
Credit: TU Wien
The theoretical simulations for the new technology were performed in the team of Prof. Florian Libisch and Prof. Joachim Burgdörfer at TU Wien. The experiment involved the group of Prof. Markus Morgenstern at RWTH Aachen and the team around Nobel-prize laureates Andre Geim and Kostya Novoselov from Manchester who prepared the samples. The results have now been published in Nature Nanotechnology.
Tuning electron energies
„For many applications in the field of quantum technologies one requires a quantum system were electrons occupy two states - similar to a classical switch - on or off, with the difference that quantum physics also allows for arbitrary superpositions of the on and off states" explains Florian Libisch from the Institute for Theoretical Physics at TU Wien.
A key property of such systems is the energy difference between those two quantum states: "Efficiently manipulating the information stored in the quantum state of the electrons requires perfect control of the system parameters. An ideal system allows for continuous tuning the energy difference from zero to a large value" says Libisch.
For systems found in nature - for example atoms - this is usually difficult to realize. The energies of atomic states, and hence their differences, are fixed. Tuning energies becomes possible in synthetic nanostructures engineered towards confining electrons. Such structures are often referred to as quantum dots or "artificial atoms".
Two ultra-thin materials: graphene and hexagonal boron nitride
The international research team of TU Wien, RWTH Aachen and the University of Manchester now succeeded in developing a new type of quantum dots which allow for much more accurately and widely tunable energy levels of confined electrons than before. This progress was made possible by combining two very special materials: graphene, a conductive single atomic layer of carbon atoms, and hexagonal boron nitride, also a single layer of material quite similar to graphene except that it is insulating.
Exactly like graphene boron nitride also forms a honeycomb lattice. "The honeycombs in graphene and hexagonal boron nitride are, however, not exactly of equal size" explains Florian Libisch. "If you carefully put a single layer of graphene on top of hexagonal boron nitride, the layers cannot perfectly match. This slight mismatch creates a superstructure over distances of several nanometers, which results in an extremely regular wave-like spatial oscillation of the graphene layer out of the perfect plane."
As the extensive simulations at TU Wien show, exactly these oscillations in graphene on hexagonal boron nitride form the ideal scaffold to control electron energies. The potential landscape created by the regular superstructure allows for accurately placing the quantum dot, or even moving it continuously and thus smoothly changing its properties. Depending on the exact position of the tip of the scanning tunneling microscope, the energy levels of the electronic states inside the quantum dot change. "A shift by a few nanometers allows for changing the energy difference of two neighboring energy levels from minus five to plus ten millielectronvolts with high accuracy - a tuning range about fifty times larger than previously possible", explains Florian Libisch.
As a next step, the tip of the scanning tunneling microscope could be replaced by a series of nanoelectronic gates. This would allow for exploiting the quantum dot states of graphene on hexagonal boron nitride for scalable quantum technologies such as "valleytronics".
„This emerging new field is quickly becoming a center of attention", comments Florian Libisch. „There are multiple potential technological applications of these atomically thin materials - that is also why the TU Wien has also very recently established a special doctoral college focused on two-dimensional materials."
Dr. Florian Libisch
Institut für Theoretische Physik
Technische Universität Wien
Wiedner Hauptstraße 8-10, 1040 Wien
Florian Aigner | EurekAlert!
Structured light and nanomaterials open new ways to tailor light at the nanoscale
23.04.2018 | Academy of Finland
On the shape of the 'petal' for the dissipation curve
23.04.2018 | Lobachevsky University
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
24.04.2018 | Information Technology
24.04.2018 | Earth Sciences
24.04.2018 | Life Sciences