The connection between a crumpled sheet of paper and quantum technology: A research team at the EPFL in Lausanne (Switzerland) and the University of Konstanz (Germany) uses topology in microwave photonics to make improved systems of coupled cavity arrays.

Smaller, more versatile, and more powerful: a team of physicists from Lausanne and Konstanz has developed advanced quantum technology components in the form of novel coupled cavity arrays (CCAs). Made from the inorganic compound niobium nitride, these CCAs feature high kinetic inductance, making them particularly well-suited for superconducting applications and a promising platform for optimized qubits in future quantum computers. They also open new possibilities for quantum simulations, serving as controlled model systems to study the behaviour of more complex quantum matter. The topology of the CCAs plays a crucial role in their function. Co-author Oded Zilberberg from the University of Konstanz explains how this is connected to the simple act of crumpling a sheet of paper.

A question of topology
For quantum physicists, "topology" describes how the overall arrangement of a system influences its individual parts — and how the details, in turn, shape the whole. It raises questions such as: How do surroundings affect physical processes? And can understanding the system's topology help predict the behaviour of its components?
While the concept sounds abstract, it can be explained with a simple analogy. Imagine a sheet of paper. If you crumple it in the centre, creases will form not only in the middle but also along the edges. Now, suppose you can only observe the edges. If you see wrinkles there, it is likely that the centre is crumpled too. In this way, the edges provide information about the unseen interior.
Oded Zilberberg’s research follows a similar logic. Instead of studying folds in paper, he examines the topology of photons — the elementary building blocks of light — moving inside a structured material. A pioneer in topological photonics, Zilberberg investigates how the global structure of quantum systems affects their internal dynamics. His work asks whether optimizing a system’s topology could enhance quantum behaviour, and whether careful observation of a system’s boundaries can reveal the hidden physics at its core.

"Topology-inspired disorder meter"
In a joint project with the EPFL, Zilberberg uses an approach very similar to the example of the crumpled paper. Disorder inside a physical system ("bulk") extends to its edges ("boundaries"). The research team used this to their advantage in the new CCAs. Although the physicists cannot see directly into the middle of a system, they can, however, observe the boundaries and use this information to draw conclusions about the bulk. This is how the researchers detect disorder and disruptions in the CCAs and ensure they work smoothly. Oded Zilberberg calls his method a "topology-inspired disorder meter", and this innovative measurement method contributed to the development of the novel CCAs.

The findings were published in April 2025 in Nature Communications: https://www.nature.com/articles/s41467-025-58595-8

Key facts: Original publication: Jouanny, V., Frasca, S., Weibel, V.J., Zilberberg, O., Scarlino, P. et al. High kinetic inductance cavity arrays for compact band engineering and topology-based disorder meters. Nat Commun 16, 3396 (2025). DOI: https://doi.org/10.1038/s41467-025-58595-8 Link: https://www.nature.com/articles/s41467-025-58595-8 Joint research project of the École Polytechnique Fédérale de Lausanne (EPFL) and the University of Konstanz. Professor Oded Zilberberg leads the research team "Quantum engineered systems" at the University of Konstanz. He is a member of the Collaborative Research Centre SFB 1432 "Fluctuations and Nonlinearities in Classical and Quantum Matter beyond Equilibrium".