On-demand coherent perfect absorption in complex scattering systems: time delay divergence and enhanced sensitivity to perturbations

TL;DR

This paper develops a theoretical framework linking coherent perfect absorption (CPA) to phase singularities and time delay divergence in complex scattering systems, demonstrating on-demand CPA and enhanced sensitivity to perturbations through experiments with a chaotic cavity.

Contribution

It provides a rigorous theoretical explanation of CPA phenomena, relates it to phase singularities and time delay, and demonstrates on-demand CPA with programmable meta-atoms and high sensitivity to perturbations.

Findings

CPA is associated with phase singularity and diverging time delay.

On-demand CPA can be achieved at arbitrary frequencies with programmable meta-atoms.

CPA condition shows optimal sensitivity to system perturbations.

Abstract

Non-Hermitian photonic systems capable of perfectly absorbing incident radiation recently attracted much attention both because fundamentally they correspond to an exotic scattering phenomenon (a real-valued scattering matrix zero) and because their extreme sensitivity holds great technological promise. The sharp reflection dip is a hallmark feature underlying many envisioned applications in precision sensing, secure communication and wave filtering. However, a rigorous link between the underlying scattering anomaly and the sensitivity of the system to a perturbation is still missing. Here, we develop a theoretical description in complex scattering systems which quantitatively explains the shape of the reflection dip. We further demonstrate that coherent perfect absorption (CPA) is associated with a phase singularity and we relate the sign of the diverging time delay to the mismatch between excitation rate and intrinsic decay rate. We confirm our theoretical predictions in experiments based on a three-dimensional chaotic cavity excited by eight channels. Rather than relying on operation frequency and attenuation inside the system to be two free parameters, we achieve "on-demand" CPA at an arbitrary frequency by tweaking the chaotic cavity's scattering properties with programmable meta-atom inclusions. Finally, we theoretically prove and experimentally verify the optimal sensitivity of the CPA condition to minute perturbations of the system.