Observation of broadband super-absorption of electromagnetic waves through space-time symmetry breaking

Abstract

Using time as an additional design parameter in electromagnetism, photonics, and wave physics is attracting considerable research interest, motivated by the possibility to explore physical phenomena and engineering opportunities beyond the physical limits of time-invariant systems. However, despite substantial theoretical promise, the practical realization and observation of many new effects and capabilities leveraging such temporal degrees of freedom have remained elusive. Here, we report the first experimental demonstration of enhanced broadband absorption of electromagnetic waves in a continuously modulated time-varying system, exceeding one of the key theoretical limits of linear time-invariant absorbers. This is achieved by harnessing the frequency-wavevector transitions and enhanced interference effects enabled by breaking both continuous space- and time-translation symmetries in a periodically time-modulated absorbing structure operating at radio-frequencies. Furthermore, we demonstrate broadband coherent wave absorption using a secondary control wave, observing a nearly perfect, reconfigurable, anti-reflection effect over a broad continuous bandwidth. Our findings provide new insights to challenge existing paradigms on the limits of wave absorption and may pave the way to the development of devices that operate in a regime fundamentally beyond the reach of any linear time-invariant system.