Semiconductor quantum dot based quantum technologies: status, challenges and prospects
Prof. Dr. Sven Höfling (Technische Physik, Universität Würzburg)

We will summarize recent progress made within our group on self-assembled quantum dot device development for quantum repeater and quantum computer applications. A particular emphasis will be on semiconductor quantum dots embedded in circular Bragg grating cavities. For scalability, spatially deterministic placement of quantum dots in bullseye cavities is pursued and tuning by electric and strain fields are implemented. To apply electric fields, a new device design for electrically contactable circular Bragg grating cavities in labyrinth geometry is employed.
In(Ga)As/GaAs quantum dots (QDs) are very attractive candidates to confine single excitons and single spins serving as solid state qubits in a mature semiconductor platform. While these qubits can be directly manipulated by optical means, both optical and electrical excitation of the QDs can be implemented to efficiently generate single photons or entangled photon pairs on demand. Light-matter interaction in coupled quantum dot-cavity systems can be widely controlled by embedding the QDs into microcavities.
In this presentation, we will summarize recent progress made within our group and plans on device development with self-assembled quantum dots intended for quantum repeater and quantum computer applications [1]. A particular emphasis will be on semiconductor quantum dots embedded in circular Bragg grating cavities [2,3]. For scalability, spatially deterministic placement of quantum dots in bullseye cavities is pursued and techniques for tuning by electric and strain fields are implemented. To apply electric fields, a new device design for electrically contactable circular Bragg grating cavities in labyrinth geometry is employed [4]. We report on the challenges experienced in obtaining high performance devices based on circular Bragg grating cavities and figures of merits achieved, outlining the prospects for these devices in quantum technology applications.

We are grateful for financial support of this work by the German Federal Ministry of Education and Research (BMBF) within the projects Q.Link.X, QR.X, MHLASQU, PhotonQ and QD-E-QKD. Expert technical assistance by Silke Kuhn, Adriana Wolf and Margit Wagenbrenner is gratefully acknowledged.

1. C.-Y. Lu and J.-W. Pan, Nature Nanotechnology 16, 1294-1296 (2021)
2. J. Scheuer and A. Yariv, IEEE J. Quantum Electron. 39, 1555-1562 (2003)
3. M. Davanco, M. T. Rakher, D. Schuh, A. Badolato, and K. Srinivasan, Appl. Phys. Lett. 99, 041102 (2011)
4. Q. Buchinger, S. Betzold, S. Höfling and T. Huber-Loyola, Appl. Phys. Lett. 122, 111110 (2023)