As part of a project funded under the Collaborative Research Centre / TRR 142, Paderborn researchers from the Department of Physics and the Institute for Photonic Quantum Systems (PhoQS) have succeeded in manu­facturing quantum dots that glow in the optical C-band at wavelengths of 1530 to 1565 nanometers. This is particularly special as it is the first time that quantum dots like these have been manu­factured by the local droplet etching and subsequent filling of nanoholes in an indium aluminium arsenide / indium gallium arsenide system lattice-matched to indium phosphide substrates.

In the future, these quantum dots could for example be used as a source of entangled photons, which might be relevant for innovative encryption systems involving quantum techno­logies. Luminescence in the optical C-band is particularly relevant here: slowdown in fibre optic networks is minimal at this wavelength, enabling potential future use with the current network. The team, consisting of Dennis Deutsch, Christopher Buchholz, Viktoryia Zola­tanosha, Klaus Jöns and Dirk Reuter, etched nano­holes in an indium aluminium arsenide surface and filled them with indium gallium arsenide. “One critical element of manu­facturing quantum dots, if they are to be used for generating entangled photons, is lattice matching. If this is not performed, it causes tension in the quantum dot, which can dispel the quantum mechanical entangle­ment of the photons generated”, Denis Deutsch explains.

Manufacturing quantum dots by filling droplet-etched holes is not new, but unlike in previous processes, the researchers used lattice matching to indium phosphide rather than gallium arsenide. The change of material enabled them to achieve emission in the C-band. As well as lattice matching materials, the symmetry of quantum dots is also a key factor in their suita­bility as an entangled photon source. The researchers therefore also statis­tically evaluated and examined the symmetry of numerous holes manufactured using different parameters.

This is a long way from being techni­cally imple­mentable, but the method is already demonstrating its potential for manufacturing quantum dots. This is because in the future, quantum computing is likely to be far superior to traditional computers when it comes to encryption. The phenomenon of entanglement is a promising approach to securely exchanging encrypted data, as any attempts to eavesdrop are exposed thanks to the laws of physics. Since entangled photons are exchanged via fiber optic cables, it is essential that trans­mission should be as low-loss as possible. “Manu­facturing photons in the particularly low-loss optical C-band is therefore a major step forward in encryption using entangled photons”, Deutsch concludes. (Source: U. Paderborn)

Reference: D. Deutsch et al.: Telecom C-band photon emission from (In,Ga)As quantum dots generated by filling nanoholes in In_0.52Al_0.48As layers, AIP Adv. 13, 055009 (2023); DOI: 10.1063/5.0147281

Link: Optoelectronic materials and devices, Dept. of Physics, University of Paderborn, Paderborn, Germany