Symmetries play a key role in many areas of modern physics. For example, the symmetry-breaking paradigm describes how various phases of matter emerge. In magnetism, spontaneous symmetry breaking leads to well-known phases of ferromagnets and antiferromagnets. Ferromagnets have a net magnetization, while antiferromagnets have atomic magnetic moments that cancel out. Surprisingly, recent research shows this magnetic dichotomy, developed in the 1930s, is incomplete [1-5]. In this talk, we introduce our recently developed classification of magnetic phases based on spin-lattice symmetries. These are pairs of operations in spin and lattice space. This unorthodox perspective has led us to identify two unconventional magnetic phases: altermagnets [4] (see figure) and antialtermagnets [5]. Like antiferromagnets, both have compensated magnetic order and thus no net magnetization. But unlike antiferromagnets—and similar to ferromagnets—they induce spin polarization in the electronic structure. The key distinction between altermagnets and antialtermagnets lies in their behaviour under time-reversal symmetry. Altermagnets break time-reversal symmetry in their electronic structure, resulting in features like d-wave spin order [2]. In contrast, antialtermagnets preserve time-reversal symmetry and exhibit properties such as p-wave spin order [5,6]. We’ll also explore how the concept of altermagnetism was inspired by our earlier theoretical prediction[1-2] and experimental observation of an unconventional spontaneous Hall effect[7]. Additionally, we’ll highlight recent photoemission experiments that have confirmed altermagnetic order in materials like MnTe and CrSb [8]. Finally, we’ll discuss the broader implications of altermagnetism and spin symmetries. These findings have potential applications in areas such as spintronics, magnonics, topological materials, 2D materials, and multiferroics [9]—all of which could lead to faster, smaller, and more energy-efficient AI-era information technologies [1,9].

Precise numerical evaluation of Feynman integrals plays a central role in particle physics. While some methods focus on individual phase-space points, others exploit differential equations to efficiently propagate results across kinematic regions. LINE is a novel open-source program that integrates both strategies within a single tool, computing boundary values and propagating them accordingly. Written primarily in C, it is designed for performance and scalability, enabling large-scale computations on clusters without relying on proprietary software. In this talk, I will introduce the core ideas behind LINE and present a few representative applications.

Synthetic antiferromagnets are magnetic multilayers consisting of two or more ferromagnetic layers that are coupled antiferromagnetically. They play an important role in spintronic devices, e.g., as field sensors, and as synthetic materials for fundamental explorations. In this talk, I will highlight the use of synthetic antiferromagnets for quantum information science with spin waves, i.e., for quantum magnonics. Examples that are discussed are unidirectionally-coupled magnetic layers that give rise to magnon quantum amplification, and new ways to entangle magnons between two ferromagnetic layers. Both these examples rely on the possibility to engineer both the interactions between the layers, and the interactions of the magnetic layers with the environment. This tunability highlights the potential of synthetic antiferromagnets for quantum magnonics.

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).