Quantum photonics with semiconductor quantum dots
Jun.-Prof. Dr. Michael Zopf (Leibniz Universität Hannover, Institut für Festkörperphysik)

This talk explores the rapidly evolving field of quantum technologies, with a particular focus on semiconductor quantum dots (QDs) and their potential in quantum communication and distributed quantum computing. Quantum dots are excellent sources of single and entangled photons and offer significant tunability in their optical properties through variations in material composition, shape, and confinement. Our work focuses on epitaxially grown GaAs/AlGaAs QDs that emit near the optical transitions of rubidium or the zero-phonon line of silicon-vacancy centres [1]. There is strong potential for such QDs in hybrid systems, which are vital for future quantum repeaters and extended quantum networks [2]. Several milestone experiments have been realized, incorporating single quantum dots. These include entanglement swapping between photon pairs [3] and quantum key distribution (QKD) experiments between Hannover and Braunschweig [4]. In order for QDs to realise their full potential in quantum technology applications, it is imperative to realize a seamless integration of QDs into photonic devices, with the objective of enhancing the efficiency of photon extraction and optimising the coupling to fibre networks. This necessitates the development of innovative strategies in the fields of optical positioning, photonic design and fabrication. A calibration model is introduced with the objective of enhancing the accuracy of wide-field optical positioning for the alignment of solid-state single photon emitters within photonic nanostructures. This is expected to result in a significant increase in the yield of high performance quantum photonic devices. Furthermore, the development of hybrid circular photonic crystal gratings for the generation of entangled photon pairs at telecom wavelengths represents a promising advancement for direct coupling efficiency into single-mode fibres [5].

[1] X. Cao, J. Yang, T. Fandrich, Y. Zhang, E. P. Rugeramigabo, B. Brechtken, R. J. Haug, M. Zopf, and F. Ding, Nano Letters 23, 6109 (2023).
[2] P. van Loock, W. Alt, C. Becher, O. Benson, H. Boche, C. Deppe, J. Eschner, S. Höfling, D. Meschede, P. Michler, et al., Advanced Quantum Technologies 3, 1900141 (2020), https://advanced.onlinelibrary.wiley.com/doi/pdf/10.1002/qute.201900141.
[3] M. Zopf, R. Keil, Y. Chen, J. Yang, D. Chen, F. Ding, and O. G. Schmidt, Phys. Rev. Lett. 123, 160502 (2019).
[4] J. Yang, Z. Jiang, F. Benthin, J. Hanel, T. Fandrich, R. Joos, S. Bauer, S. Kolatschek, A. Hreibi, E. P. Rugeramigabo, et al., Light: Science & Applications 13, 150 (2024), ISSN 2047-7538.
[5] C. Ma, J. Yang, P. Li, E. P. Rugeramigabo, M. Zopf, and F. Ding, Opt. Express 32, 14789 (2024).