Topological photonics and terahertz quantum sensing
Prof. Georg von Freymann (TU Kaiserslautern)

Photonic quantum simulation and sensing

Georg von Freymann1,2
1Physics Department and Research Center OPTIMAS, Rheinland-Pfälzische Technische Universität Kaiserslautern Landau RPTU, 67663 Kaiserslautern, Germany
2Fraunhofer Institute for Industrial Mathematics ITWM, 67663 Kaiserslautern, Germany

Applications of quantum technology are highly sought-after and thus supported by public funding agencies. However, the meaning of application varies depending on who you talk to: In the physics community application often means a useful laboratory implementation, while from an industrial perspective, application means solving a measurement problem in production or even creating a saleable product.
To address the physics perspective, I will discuss 3D µ-printed photonic quantum simulators based on coupled waveguide system, focusing on topological protection and Floquet (time-periodic) driving. Such experimental model systems allow for studying these phenomena under very well controlled conditions. Examples are periodic driving of topologically protected edge modes in the one-dimensional Su-Schrieffer-Heeger-chain leading to depopulation of the edge mode despite topological protection [1], periodic driving of two-dimensional honey-comb-lattices establishes topological protection in an otherwise topologically trivial model system [2], switching of topological protection via excitation with and without orbital angular momentum of light [3], and establishing higher-order topological insulators using p-orbitals of the waveguides [4].
From the industry perspective I discuss recent results for terahertz quantum-sensing with undetected photons [5] allowing to measure terahertz spectral properties with visible light only, enabling both single-shot layer thickness measurements as well as spectroscopy.

[1] Z. Cherpakova, C. Jörg, et al., Limits of topological protection under local periodic driving, Light: Science&Applications 8, 63 (2019).
[2] C. Jörg, et al., Dynamic defects in photonic Floquet topological insulators, New J. Phys. 19, 083003 (2017).
[3] C. Jörg, et al., Artificial gauge field switching using orbital angular momentum modes in optical waveguides, Light: Science&Applications 9, 150 (2020).
[4] J. Schulz, J. Noh, et al., Photonic quadrupole topological insulator using orbital-induced synthetic flux, Nature Communications 13, 6597 (2022)
[5] M. Kutas et al, Terahertz Quantum Sensing, Science Advances 6, eaaz8065 (2020)