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    Quantum Emission Based on Vacancy Defects


    If you remove a single atom from a regular lattice of silicon and carbon atoms, the crystal exhibits completely new properties. University of Würzburg physicists, leading experts in this field, have had several impressive successes in their research.

    Nach dem Beschuss mit Neutronen zeigen Siliziumkarbid-Kristalle überraschende Eigenschaften: Sie emittieren Mikrowellen. (Grafik: Hannes Kraus)
    Nach dem Beschuss mit Neutronen zeigen Siliziumkarbid-Kristalle überraschende Eigenschaften: Sie emittieren Mikrowellen. (Grafik: Hannes Kraus)

    Nowadays, almost everybody is familiar with lasers while only specialists may ever have heard of a maser. Although both devices are based on the same principle, the laser has long since found its place in our everyday technologies while the maser is still an expensive niche product, which is rarely used. This might change in the near future: Professor Vladimir Dyakonov, head of the Department for Experimental Physics VI at the University of Würzburg, and his research associate, Dr. Georgy Astakhov, may have figured out a way to help the maser start a success story similar to that of the laser. The results of their work are reported in the current issue of the prestigious journal Nature Physics.

    Maser: generator of microwaves

    "Today's masers work only at extremely low temperatures near absolute zero and therefore require considerable cooling. As a consequence, they are not suitable for application in everyday technology," says Vladimir Dyakonov. Like a laser, a maser emits an electromagnetic wave with special physical properties. The difference is that a laser emits visible light while a maser sends out microwaves. These carry significantly less energy than laser light. Their wavelength ranges from a few millimeters to meters whereas lasers operate at wavelengths of a few hundred nanometers. Nevertheless, masers are of technological interest: For instance, they are very useful for communication purposes and as they are extremely sensitive to microwaves, they are well suited to be used in sensors and measuring devices.

    A missing atom changes the properties

    Astakhov and Dyakonov have now succeeded in providing proof of principle that a maser can operate even at room temperature. For this purpose, the two physicists used a material with well-established technological application: a crystal of silicon and carbon atoms – silicon carbide. "We hit silicon crystals with neutrons, thus removing individual atoms from the crystal lattice in a targeted way," says Astakhov describing the sample preparation in the laboratory. A vacancy defect in an otherwise regular lattice: This affects the neighboring bonding partners, which react in a way that makes the crystal change its properties. In this case, the crystal sent out microwaves when irradiated with light – even at room temperature.

    "The method works in principle": This has been demonstrated with the silicon carbide crystal for the first time worldwide by the Würzburg physicists; with this discovery, their study made it to publication in Nature Physics. However, a number of as yet unanswered questions need to be clarified before the first silicon carbide maser can be put on the market. This would also require a "dedicated technological development".

    New DFG research project started

    As to the search for answers to the unanswered questions, Georgy Astakhov is well positioned to succeed. Just a few weeks ago, the German Research Foundation accepted his new research project on vacancy defects in silicon carbide crystals. With about 300,000 euros worth of funding for an additional research assistant and for material, Astakhov is going to examine the fundamental physical processes in the crystal over the coming three years.

    The development of a maser is not the only technological innovation envisioned in this research project. The modified silicon carbide is promising for yet another application – as a semiconductor and storage medium in novel quantum computers. Such computers process information in the form of so-called qubits. These can be based on the spin of electrons. In simplified terms, the spin represents their angular momentum. It can point in several directions, for which reason it can contain much more information than a classical bit. This could be used for enhanced information processing.

    A tried and tested material

    Another advantage of the crystal: Silicon carbide is widely used in technological applications. Light emitting diodes, transistors, micro-electro-mechanical components or sensors made from this material are already on the market. Therefore, the know-how for processing this material on a large scale has long been available.

    Room-temperature quantum microwave emitters based on spin defects in silicon carbide. H. Kraus, V. A. Soltamov, D. Riedel, S. Väth, F. Fuchs, A. Sperlich, P. G. Baranov, V. Dyakonov and G. V. Astakhov. Nature Physics, DOI: 10.1038/NPHYS2826

    Contact person

    Prof. Dr. Vladimir Dyakonov, T: +49 (0)931 31-83111
    email: dyakonov@physik.uni-wuerzburg.de

    Dr. Georgy Astakhov, T: +49 (0)931 31-85125
    email: astakhov@physik.uni-wuerzburg.de


    By Gunnar Bartsch