Thought To Be Impossible: Scientists Break Century-Old Physics Barrier

Scientists in Korea achieved the first experimental realization of bound states in the continuum in a single resonator, opening doors to ultra-efficient wave control for future tech.

A research team from POSTECH (Pohang University of Science and Technology) and Jeonbuk National University has achieved a groundbreaking feat: the complete confinement of mechanical waves within a single resonator—something long considered theoretically impossible. Their study, published on April 3 in Physical Review Letters, represents a significant advance in solving the century-old puzzle of bound states in the continuum (BIC).

Resonance, the amplification of waves at specific frequencies, underpins many everyday technologies, including smartphones, ultrasound imaging, and radio systems. However, conventional resonators gradually dissipate energy, requiring continuous input to sustain their operation.

Nearly 100 years ago, Nobel Prize winners John von Neumann and Eugene Wigner introduced a radical idea: under specific conditions, it might be possible for waves to remain confined indefinitely, without leaking energy. These so-called bound states in the continuum (BIC) are akin to whirlpools that stay fixed in place, even as a river flows around them. Yet for decades, scientists assumed such states could not exist within a compact, single-resonator system—until now.

Achieving BIC in a Single Resonator

Now, the research team has broken this long-standing theoretical boundary by successfully realizing BIC in a single particle.

Using a system of cylindrical granular particles—small solid rods made of quartz—the researchers built a highly tunable mechanical platform. By precisely adjusting how the cylinders touch each other, they could control the way mechanical waves interact at the contact boundaries.

Under special alignment, a wave mode became fully confined within a single cylinder without any energy escaping into the surrounding structure. This so-called polarization-protected BIC was not just theoretical—it was observed in real experiments. Even more remarkably, the system achieved quality factors (Q-factors) over 1,000, a measure of how efficiently a resonator stores energy with minimal loss.

What happens when many of these special cylinders are connected in a chain? The team discovered that the trapped wave modes could extend throughout the chain without dispersing—a phenomenon known as a flat band.

“It’s like tossing a stone into a still pond and seeing the ripples remain motionless, vibrating only in place,” said lead author Dr. Yeongtae Jang. “Even though the system allows wave motion, the energy doesn’t spread—it stays perfectly confined.” This behavior is described as a Bound Band in the Continuum (BBIC) and opens new possibilities for energy harvesting, ultra-sensitive sensors, and even advanced communications.

Implications and Future Applications

“We have broken a long-standing theoretical boundary,” said Professor Junsuk Rho, who leads the research. “While this is still in the fundamental research phase, the implications are significant—from low-loss energy devices to next-generation sensing and signal technologies.”

Reference: “Bound States to Bands in the Continuum in Cylindrical Granular Crystals” by Yeongtae Jang, Seokwoo Kim, Dongwoo Lee, Eunho Kim and Junsuk Rho, 3 April 2025, Physical Review Letters.
DOI: 10.1103/PhysRevLett.134.136901

This research was supported by the Mid-Career Research Program of the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT, as well as the POSCO-POSTECH-RIST Convergence Research Center.

Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.