Coherent Perfect Absorption: Zero Reflection Without Linewidth Suppression

TL;DR

This paper clarifies that coherent perfect absorption (CPA) reduces reflection without narrowing spectral linewidths and does not induce true mode splitting, emphasizing careful data interpretation in cavity and polaritonic systems.

Contribution

The study provides a detailed analysis showing CPA does not suppress linewidths or cause true mode splitting, correcting misconceptions and guiding proper data presentation.

Findings

CPA drives on-resonance reflection to zero without linewidth suppression.

Apparent spectral narrowing near CPA is a visual artifact, not a true effect.

Logarithmic plots can falsely suggest mode splitting, which linear spectra do not confirm.

Abstract

Motivated by recent claims, we revisit how coherent perfect absorption (CPA) influences cavity and polaritonic linewidths. Using standard input output theory and measurements on single port bare microwave cavities and cavity magnon hybrids, we find that CPA drives the on resonance reflection to zero while the spectral width remains set by the total decay rate. Apparent narrowing observed near CPA is found to be a visual artifact that does not remain upon quantitative analysis. Extending the analysis to cavity magnomechanics, we show that logarithmic plots can exhibit apparent polaromechanical normal mode splitting, whereas linear scale spectra display no true splitting. These results clarify when CPA modifies amplitudes versus spectral poles, offer practical guidance for data presentation, and indicate that CPA alone is not a route to linewidth suppression or polaromechanical mode splitting in the linear, weak-probe regime.