GaAs Quantum Dots: from Form to Function

• Applicant: Dr. Arne Ludwig
• Subject Area: Experimental Condensed Matter Physics ; Synthesis and Properties of Functional Materials
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559683823

The goal of this project is to provide a comprehensive experimental and theoretical description of the charge and spin properties of strain-free GaAs quantum dots (QDs), focusing on hole-spin properties. QDs form the basis of excellent single-photon sources. The sources are fast: a photon can be created each nano-second. The sources are also pure (small probability of multi-photon emission) and coherent (high two-photon interference visibility). Furthermore, a QD can be equipped with a single electron. Exploiting the spin degree of freedom, a QD turns into a source of cluster states. A notable example is the 3-photon GHZ state, a so-called resource state. As such, QDs will play an important role in quantum technology, specifically quantum communication and photonic quantum information processing. Traditional QDs are InGaAs in a GaAs host, formed via the Stransky-Krastanov process, resulting in highly strained QDs. An alternative method uses Al droplets to etch nano-holes on an AlGaAs surface, filled with GaAs to form strain-free GaAs/AlGaAs QDs. These QDs exhibit extraordinary properties: high-visibility two-photon interference (93%), high-fidelity entangled photons (98%), and long spin superposition preservation (100 microseconds). GaAs QDs emit in the red spectrum, tunable to Rb lines, essential for single-photon memory. GaAs QD photons can be frequency-converted to the telecom C-band, a convenient feature. GaAs QDs differ from InGaAs/GaAs QDs in structure and strain, affecting electron and hole states. This project involves Swiss, German, and Polish research groups, combining experimental semiconductor physics, materials science, and atomistic theory. We aim to understand GaAs QDs’ key physical properties through advanced growth techniques, spectroscopic methods, and atomistic-level simulations, supporting their applications in quantum technologies. The proposed research aims at answering two key questions regarding the physical properties of strain-free GaAs QDs. The answers will determine their role in quantum technologies. The questions are: How are the key physical properties of the GaAs QDs determined by their shape, size, composition and environment? And how can one design strain-free QDs for optimal quantum control?

• DFG Programme: Research Grants
• International Connection: Poland, Switzerland
• Partner Organisation: Narodowe Centrum Nauki (NCN)
• Cooperation Partners: Professor Dr. Krzysztof Gawarecki; Professor Dr. Pawel Machnikowski; Professor Dr. Richard Warburton