When Felix describes the model they devised to represent quantum systems with internal dynamics, it’s somewhat reminiscent of theoretical mechanics: “We use coupled quantum rotors, which are essentially several coupled rings, each with a particle flying around it that experiences a jolt at regular intervals.“ Of course, these quantum rotors do not map the internal dynamics of real qubits – such as those in atoms – on a one-to-one basis, just as there are no massless rods. But that is precisely what fascinates Felix about theoretical physics. He seems glad he doesn’t have to grapple with the many details of a real laboratory experiment. “We start with just a few basic assumptions, and they take us incredibly far!” The high level of abstraction provides very general and powerful tools, the physicist adds. Their model of coupled quantum rotors is also very insightful. “Our research aims to help prepare such fully entangled states – for example, in a quantum computer – as efficiently as possible, or to identify any obstacles that might arise in the process.”

Even though Felix prefers theory in physics, things are different when it comes to music: “We’re always very experimental.” By “we,” he means himself and his roommate, with whom he often holds spontaneous jam sessions in the living room in the evenings. “We have a few guitars, a bass, lots of small instruments, and a sound system.” Sometimes a few friends join them to make music, he says, adding enthusiastically: “It’s rarely particularly sophisticated, but it’s a ton of fun!” Felix emphasizes that his roommate is also one of his best friends. They met during their year abroad together in Vancouver. At the University of British Columbia, the physics major attended a few lectures between his bachelor’s and master’s degrees. But they also really enjoyed their free time there. “The university campus has two beaches!” Felix gushes. In the winter, they regularly went skiing in the nearby mountains; in the summer, they went hiking. “That was probably the best time of my life…,” he sighs, somewhat lost in thought as he recounts it, then quickly adds: “Well, of my life so far.”

On the trail of exotic spin systems

After his year abroad, Felix returned to Würzburg. For his master’s thesis, he worked with the Kitaev model, a popular model in theoretical solid-state physics. The model describes the behavior of interacting spins on a hexagonal lattice, also referred to as honeycomb lattice, meaning the spins are arranged so that they form the vertices of a hexagon. For physicists, the Kitaev model is interesting because it describes an exotic state of matter: even at absolute zero, the spins do not freeze but remain in constant quantum mechanical motion, which is why this state of matter is called a quantum spin liquid. For Felix not exotic enough. “In my master’s thesis, I examined what happens when we apply this beautiful model to a curved geometry,” he explains, bringing up the concept of hyperbolic lattices. Since the beginning of his bachelor’s thesis, hyperbolic lattices have been a passion project for him, the theorist says, and he enthusiastically launches into an explanation. “Fundamentally, a lattice is something used to discretize space. That means you can’t simply occupy any point, but only very specific points” – an important concept in solid-state physics, where the crystal lattice describes the regular arrangement of atoms in crystalline solids. On a flat surface, there are only a limited number of possible lattices, Felix continues, trying to illustrate the point: You can arrange triangles, quadrilaterals, and hexagons on a table so that the table’s surface is completely filled without any gaps, and in such a way that the polygons do not overlap. This does not work with pentagons or 17-gons. Only when you allow the surface to curve – with the curvature mathematically following a hyperbola – can you arrange pentagons and 17-gons seamlessly and without overlap. “And not just these,“ Felix enthuses. “There are an infinite number of hyperbolic lattices. That’s incredibly cool.“

In his master’s thesis, which ultimately led to a publication, the physicist placed the spins of the Kitaev model at the vertices of nonagons. “You often discover something new when you take a familiar model but then deliberately vary certain parameters, such as the geometry on which the system lives,” Felix describes the motivation behind his thesis. And that is exactly what happened. The spin system that he and his colleagues in Würzburg investigated can assume a state corresponding to a quantum spin liquid with very specific properties. “You can’t find a comparable state in non-curved space.” The mere fact that this state exists is a very exciting result, Felix emphasizes, even if their spin system might seem somewhat artificial at first glance. Ultimately, these are not material systems that one would find in nature. An experimental realization – still a distant prospect, as Felix emphasizes – would amount to a synthetic material “that you cobble together in the lab.”

The master’s thesis sparked Felix’s interest in continuing his research. While searching for a doctoral position, his professor at the University of Würzburg at the time drew his attention to the doctoral fellowship program of Munich Quantum Valley. He realized just how tough the competition for the few fellowships awarded each year actually was during the second round of the selection process. Even at the interviews, to which only a few of the original applicants are invited, there were still 30 students in the running. His joy was all the greater when he learned that he had secured one of the fellowships. Above all, he’s delighted that the fellowship has allowed him to pursue his doctorate in this fantastic environment. His professor in Würzburg had recommended Frank Pollmann’s research group at TUM to him. The fellowship allows him to conduct research there regardless of the department's available funds. “The group’s expertise is immense. You can really learn a lot from them!” Felix enthuses. “I’m constantly pushing myself to my limits – not in terms of workload, but in terms of what my mind is capable of.“ That’s exactly the kind of challenge he loves: “Because you learn so much!“

Published 26 June 2026; Interview 28 May 2026