Breaking the barriers of physics a century ago: Scientists achieve perfect wave trapping with simple cylinders

The collaborative research team has successfully demonstrated complete confinement of mechanical waves within a single resonator. It was considered impossible in theory. Their findings, published in a physical review letter on April 3rd, mark a major breakthrough in the mystery of the century of the Continuum (BIC). The team graduated from Postech (Pohang University of Science and Technology) and Jeonbuk National University.

Many technologies around us (from smartphones and ultrasound devices to radios) are based on resonance, a phenomenon in which waves are amplified at a specific frequency. However, typical resonators gradually lose energy over time, requiring a constant energy input to maintain function.

Almost a century ago, Nobel Prize winners John von Neumann and Eugene Wigner proposed counterintuitive concepts. Under certain conditions, waves can be trapped indefinitely without energy leakage. These so-called bonded states of the continuum (BIC) are like vortices that remain in place even when the river flows around it. For decades, however, scientists have believed that this phenomenon cannot exist in compact single-particle systems.

Now, the researchers have broken this long-standing theoretical boundary by successfully realizing BIC with a single particle.

Researchers have built a highly adjustable mechanical platform using a system of small solid rods made of quartz. By precisely adjusting the way the cylinders touch each other, you can control how the mechanical waves interact at the contact boundary.

Under special alignment, the wave modes were completely trapped within a single cylinder without energy escaping into the surrounding structure. This so-called polarization-protected BIC was observed in real experiments rather than merely theoretical. Even more surprising, the system has achieved over 1,000 quality factors (Q factors). This is a measure of how efficiently the resonator stores energy with minimal losses.

What if many of these special cylinders are connected to the chain? The team discovered that trapped wave modes spread across the chain without dispersing. This is a phenomenon known as flat bands.

“It’s like throwing the stones into the pond and seeing the ripples still remain in motion, only vibrating in that position,” said author Dr. Yeongtae Jang. “Even if the system allows wave movement, the energy does not spread. It remains completely limited.”

This behavior is described as a bound band in a continuum (BBIC), opening up new possibilities for energy harvesting, ultra-sensitive sensors, and even advanced communication.

“We have broken years of theoretical boundaries,” said Professor Junsuk Rho, who leads the study. “This is still in the basic research phase, but its implications are important, from lowered energy devices to next-generation sensing and signaling technologies.”