New 'breathing' solitons could revolutionize information transfer

“Solitons” are waves that refuse to spread out or slow down, a stubborn breed that keeps its shape as it travels. In 1834, a Scottish engineer named John Scott Russell chased one along the Union Canal and recorded it in detail.

A new study reports a version of that wave that pulses as it goes and yet survives in systems where energy normally leaks away. 

Lead author Jonas Veenstra and his colleagues at the University of Amsterdam’s Institute of Physics (IOP) carried out the experiments with collaborators in London and Marseille. 

Solitons vanish in real materials

After Russell’s sighting, mathematicians wrote down an equation in 1895 that explains these solitary waves in shallow water.

Their equation, the KdV equation, became a template for understanding stable wave packets across physics.

The world is rarely lossless, though. Friction and drag steal energy, so even a classic soliton eventually smears out in real materials.

What makes this result different

The Amsterdam team built a tabletop metamaterial that breaks symmetry on purpose.

Key ingredient is nonreciprocity, where element A nudges element B differently than B nudges A, a behavior that can produce the non-Hermitian skin effect and strong one-way amplification in active media.

The authors introduce and stabilize a special pulsing wave called a breather that keeps moving without fading, even when the system is losing energy. 

“Breathing solitons consist of a fast beating wave within a compact envelope of stable shape and velocity,” wrote Veenstra and colleagues.

In their summary, the team noted that the asymmetry was crucial, and this insight shaped both the experimental design and the theoretical framework.

Creating stable pulsing waves

The lab setup is a chain of 50 active oscillators connected with flexible bands and powered by tiny motors, so each unit can push and sense its neighbors.

By programming an asymmetric coupling, the researchers made waves that prefer one direction and keep a tidy envelope as they travel.

In that regime the breather’s carrier oscillation sits near 5 Hz, while the envelope marches along at about 8 units per second in the experiment’s scaled coordinates.

Those numbers come straight from the team’s measurements and appear alongside the models the authors tested against the data.

The nonreciprocal link is implemented with embedded sensors, microcontrollers, and motors that inject a controlled torque bias between neighbors.

That active feedback breaks Newton’s third law at the material level and sets the stage for one-way transport.

Dynamics of breathing solitons

To explain the dynamics, the team connected their mechanical chain to two workhorse equations in nonlinear physics.

The sine-Gordon equation and the nonlinear Schrödinger equation capture how a compact envelope can host a rapid internal oscillation that beats as it moves.

Nonreciprocity and damping would normally spoil that structure. Here they create a delicate balance controlled by a mathematical fixed point and a nearby bifurcation, which together govern when a breather decays, explodes, or persists for a long time.

Discrete materials help solitons

In a continuous medium the long-lived state appears only in a tight range of parameters, so getting it is a precision act. The experiment shows that discreteness in the chain actually helps, widening the island where breathers last.

That practical twist matters if you want devices to work outside a perfect lab. Real materials are made of parts, and that granularity can stabilize waves that theory says should be fragile.

Breathers are not just eye-candy. They can shuttle information or energy while resisting loss, which is one reason optical researchers have studied breathing dissipative solitons in microresonators used for frequency combs and sensing.

A mechanical platform adds new options. Think of distributed sensors, robust signal paths in soft robots, or energy-harvesting architectures that selectively route motion where you want it.

How it fits with recent progress

This result builds on earlier work showing that nonreciprocal driving can push solitons and antisolitons in the same direction, unlocking unidirectional transport in active lattices. That mechanism was demonstrated by members of the same community in 2024.

Nonreciprocity is also tied to fresh ideas in non-Hermitian physics that reframe how waves respond to boundaries and defects. Those ideas are now appearing across optics, acoustics, and mechanics.

Russell’s canal wave was a landmark observation, but it lived in a clean natural channel and still faded with distance. Modern experiments push these waves into driven, noisy environments where old assumptions break.

Korteweg and de Vries gave physics an enduring equation, and that heritage still shows up in today’s models and simulations.

Yet the new work gives those equations a fresh twist by adding asymmetric interactions and active feedback.

Why the claims hold up

The paper pairs millimeter-scale hardware with simulations and perturbation theory, so the team can check the same behaviors in three ways.

They report that a careful balance between energy injection, dissipation, and initial conditions pins the system near the right fixed point.

Crucially, the paper notes that discreteness stabilizes breathers over a broader range of conditions than the continuum predicts.

That insight is already steering the next experiments toward two-dimensional surfaces of nonreciprocal oscillators.

The study is published in Physical Review X.

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