Sebastian Klembt is the new Chair of Experimental Physics I at the University of Würzburg. At the Cluster of Excellence ctd.qmat, he develops lasers and investigates how light can be guided with a high robustness.
How can light be guided in such a way that it remains robust along its path? This is one of the questions being investigated by Sebastian Klembt, a physicist at the University of Würzburg and a researcher at the Würzburg-Dresden Cluster of Excellence ctd.qmat – Complexity, Topology and Dynamics in Quantum Matter. He is the new Chair of Experimental Physics I in Würzburg.
Klembt’s academic career has taken him from the University of Bremen to ETH Zurich and the French National Centre for Scientific Research (CNRS) in Grenoble. Since 2015, he has been based in Würzburg. Early on, he focused on a field that is now among the most dynamic areas of modern physics: the interplay of photonics, quantum materials, and topology. Photonics is concerned with generating and controlling light and using it for technological applications. Topology, a branch of mathematics, describes robust properties that remain unchanged even when an object is deformed.
Breakthrough in light–matter states
Klembt achieved a significant breakthrough during a Marie Skłodowska-Curie Fellowship from 2016 to 2018. During this period, his team succeeded in realizing what are known as topological polaritons – states in which light and matter interact closely and propagate with exceptional robustness along predefined paths. Their direction of motion could be controlled using a magnetic field, something that is difficult to achieve with light alone. Klembt’s findings were published in Nature in 2018 and marked an important step toward novel optical quantum systems.
A milestone: the topological laser
Since 2020, Klembt has continued his research on topological lasers as an assistant professor in the Cluster of Excellence ctd.qmat – Complexity, Topology and Dynamics in Quantum Matter. He and his team achieved another major success with the first topological laser made from vertical resonators. In this new type of laser, numerous tiny lasers are coupled in such a way that they work together like a single powerful laser. The vertical resonators are microscopic optical cavities that emit
laser light perpendicular to the surface of the chip. The results were published in Science in 2021. Klembt’s approach could help make lasers more efficient, more scalable, and less susceptible to interference.
Klembt completed his habilitation in Würzburg in 2024, an important qualification on the path to a professorship in Germany. His research spans fundamental questions in physics as well as potential applications of his basic research in optoelectronic devices. A patent has already been filed for his work on topological lasers.
Between solid-state physics and photonics
Klembt pushes the boundaries between scientific disciplines. He applies concepts from solid-state and transport physics to optical systems, opening up new ways to guide light with precision. One example is the principle of topological insulators. These materials have a unique property: they are insulating in their interior, yet signals can flow along their edges unimpeded.
Together with his team, Klembt has transferred this concept to light, finding a way to guide it so that it remains remarkably robust even in the presence of disturbances or disorder. The team has also demonstrated an optical counterpart to the spin quantum Hall effect, a quantum mechanical phenomenon in which electrons with different spin states move along the edges of a material in opposite directions. With his discoveries in topological photonics, Klembt is laying the foundations for future optical components.
Research with an eye to the future
“I’m fascinated by the question of how the targeted interplay of light and matter can give rise to completely new physical properties,” says Klembt. “The most innovative concepts often emerge precisely at these interfaces. That’s where I see enormous potential for future technologies.” Klembt is currently working on optical lattices, topological lasers, two-dimensional materials, and organic emitters, among other topics.
Klembt has held the Chair of Experimental Physics I since November 2025. It is the first new appointment to the chair in almost 20 years. In his inaugural lecture, “Twisting Light and Matter: A New Perspective on Quantum Materials, Photonics and Topology,” held on June 15, 2026, Klembt outlined his research goal: a modern form of experimental physics that brings together quantum materials, photonics, and topological concepts while generating fundamental insights for the technologies of tomorrow.
ctd.qmat
The Cluster of Excellence ctd.qmat — Complexity, Topology and Dynamics in Quantum Matter — at Julius-Maximilians-Universität Würzburg and Technische Universität Dresden explores and develops novel quantum materials with tailored properties. Around 300 researchers from over 30 countries work at the interface of physics, chemistry, and materials science to lay the foundations for tomorrow’s technologies. In 2026, the cluster entered the second funding period of the German Excellence Strategy of the Federal and State Governments — with an expanded focus on the dynamics of quantum processes.