Physicists have developed a nano-scale trampoline-like device that serves as a groundbreaking phonon waveguide. (Artist’s concept.) Credit: Stock
The world’s strangest trampoline doesn’t bounce—it swings sideways and even glides around corners. But no one can jump on it, because it’s less than a millimeter tall.
Imagine a trampoline so tiny it’s just 0.2 millimeters wide, with a surface thinner than anything you’ve ever seen, only about 20 millionths of a millimeter thick. It’s full of regularly spaced, rounded triangular holes, giving it a unique, perforated design. Despite its delicate look, this trampoline is almost unstoppable. Once it starts moving, it barely loses any momentum and could keep swinging for an incredibly long time.
But it doesn’t just bounce up and down like a normal trampoline. Across its surface, different regions move in different directions, including sideways. At the center, there’s even a “trampoline within the trampoline,” a smaller area where things get even more wild. Here, the motion follows a precise triangular path, allowing vibrations to curve perfectly around corners—something rarely seen in physics.
From Bouncing to Phonons
So why design this trampoline if nobody can jump on it? Of course, this construction was not designed for people to use. The brains behind the trampoline – physicists from the University of Konstanz, the University of Copenhagen, and ETH Zurich – want to use it to demonstrate new methods of phonon transport.
The “trampoline” is actually a waveguide for phonons: a vibrating, ultra-thin membrane made of silicon nitride. Phonons are, so to speak, “sound quanta,” i.e., the elementary excitations on which vibrations of the crystal lattice of a solid are based. Using the trampoline, the physicists want to demonstrate how phonons can be directed “around corners” by means of a unique surface structure (based on mathematical topology principles) with practically no loss of momentum. This is important, for example, in microchip circuits where signals are to be directed around edges and curves.
Topological Transport with Minimal Loss
The results are impressive: using the trampoline, phonons can even be directed around tight, 120-degree curves with virtually no loss of momentum. The amount of phonons that “bounce back” instead of going around the curve is less than one per ten thousand. “This ultra-low loss is on par with contemporary telecommunication devices,” Konstanz physicist Oded Zilberberg says.
Zilberberg is interested in studying exactly these kinds of topological effects in surface structures and how they can be used in applications. He thinks that, with this method, it could be possible to build entire roads for phonons. Zilberberg created the trampoline’s specific design. His colleagues from the University of Copenhagen and ETH Zurich then put the idea into action. The research team’s results were recently published in the journal Nature.
But, would it be possible to build the trampoline for people to jump on? “I actually have thought about that”, Zilberberg smiles. “It would definitely be a fun experiment. I assume that the principle would also work with a larger scale object.” However, no one should try the “human-sized” version of the trampoline without wearing a helmet.
Reference: “A soft-clamped topological waveguide for phonons” by Xiang Xi, Ilia Chernobrovkin, Jan Košata, Mads B. Kristensen, Eric Langman, Anders S. Sørensen, Oded Zilberberg and Albert Schliesser, 4 June 2025, Nature.
DOI: 10.1038/s41586-025-09092-x
This research was conducted, in part, in the context of the Collaborative Research Centre SFB 1432 “Fluctuations and Nonlinearities in Classical and Quantum Matter beyond Equilibrium” at the University of Konstanz.
Funding: the European Research Council (ERC), Novo Nordisk Foundation, Danish National Research Foundation, Independent Research Fund Denmark, Swiss National Science Foundation (SNF), German Research Foundation (DFG), EU programme Horizon 2020, Villum Foundation, and the Marie Skłodowska-Curie programme.
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