Fabrication of drop-etched quantum dots that glow in the optical C-band.

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Symbolic image (University of Paderborn, Besim Mazhiqi)
Symbolic image (University of Paderborn, Besim Mazhiqi)

Researchers from the Department of Physics and the Institute for Photonic Quantum Systems (PhoQS) in Paderborn have successfully produced quantum dots - nanoscopic structures in which the quantum properties of matter come into play - that glow in the optical C-band at a wavelength between 1530 and 1565 nanometers as part of a project funded within the Collaborative Research Center/TRR 142. What is special is that this is the first time that such quantum dots have been successfully fabricated by local droplet etching and subsequent filling of the nano-holes in the indium aluminum arsenide/indium gallium arsenide system in a lattice-matched manner on indium phosphide substrates. In the future, these quantum dots may be used, for example, as a source of entangled photons, which may become relevant for novel encryption systems using quantum technologies. Of particular importance is the luminescence in the optical C-band: at this wavelength, the attenuation in the fiber optic network is minimal, so a possible future use is possible with the current network. The scientists have now published their results in the journal -AIP Advances-.

The team of Dennis Deutsch, Christopher Buchholz, Dr. Viktoryia Zolatanosha, Klaus Jöns and Dirk Reuter etched nanoscopic holes in an indium aluminum arsenide surface and filled them with indium gallium arsenide. -A critical point in the fabrication of quantum dots, if they are to be used for the generation of entangled photons, is the lattice matching. If this is not given, distortions occur in the quantum dot, which can break down the quantum mechanical entanglement of the generated photons-, Dennis Deutsch explains. Fabricating the quantum dots by filling drop-etched holes is not new, but unlike previous work, the researchers* used a lattice fit on indium phosphide instead of gallium arsenide. The change in materials has enabled them to achieve emission in the C-band. In addition to the lattice matching of the materials, the symmetry of the quantum dots is also an important factor in their suitability as sources of entangled photons. Therefore, numerous holes produced at different parameters were also statistically evaluated in the publication and examined for their symmetry.

Although technical application is still a long way off, the potential of this method for producing quantum dots is already becoming apparent. This is because quantum computers will presumably be significantly superior to classical computers when it comes to encryption in the future. The phenomenon of entanglement in particular is a promising approach to securely exchange encrypted data, as any eavesdropping attempt will be unmasked based on physical principles. Since the exchange of entangled photons takes place over fiber optic lines, it is essential that transmission be as low-loss as possible. -The generation of photons in the particularly low-loss optical C-band is therefore an essential step toward encryption using entangled photons," summarizes Deutsch.

To the paper: pubs.aip.org/aip/adv/article/13/5/055009/2888840