Experimental Observation of Time-Domain Bound States in The Continuum

TL;DR

This paper reports the first experimental realization of time-domain bound states in the continuum (BICs) using a modulated transmission-line network, revealing new phenomena in wave systems with broken time-translation symmetry.

Contribution

It demonstrates the experimental observation of time-domain BICs in a wave system with time-modulated impedance, a novel phenomenon predicted recently.

Findings

Time-domain BICs exhibit a well-defined peak with decaying oscillations.

The observed BIC is anti-symmetric despite symmetric modulation.

Experiments open new avenues in nonconservative wave systems with broken time-translation symmetry.

Abstract

Bound states in the continuum (BICs) are spatially localized eigenmodes that remain perfectly confined even though their energies reside within a continuum of radiating modes. BICs were predicted in 1929, but their experimental realization awaited more than 8 decades. Following their experimental observation, BICs were explored in a variety of wave systems, and found to exhibit a plethora of fundamental features such nontrivial topology and extremely high Q-factor. Recently, with foundational advances in the new field of electromagnetic waves in time-varying media, BICs were predicted to exist in the time domain, with their wavenumber embedded in a continuum of unbound momentum modes. Here, we present the first experimental realization of the time-domain Bound States in the Continuum. We use a transmission-line network with a time-modulated wave-impedance and show that a sinusoidal wave launched into the network naturally evolves into a time-domain BIC with a well-defined peak and decaying-oscillating tails. We show that the time-domain BIC is anti-symmetric despite the symmetric nature of the modulation. These experiments pave the way for exploring new phenomena in the fields of BICs and time-varying wave-systems in nonconservative regimes where time-translation symmetry is broken.