Comment on: "Coherent perfect absorption: Zero reflection without linewidth suppression"

TL;DR

This comment defends the validity of observed polaromechanical normal-mode splitting against recent criticisms, clarifying that the splitting occurs in a narrow frequency range and that the critique's decay rate measure is irrelevant to the experiment.

Contribution

The paper clarifies misconceptions about the nature of normal-mode splitting and decay rates in polaromechanical systems, reaffirming the original experimental findings.

Findings

Normal-mode splitting occurs in a narrow frequency range around CPA.

The decay rate at the pole does not characterize the effective decay relevant to CPA.

Criticisms based on the total decay rate are either false or irrelevant.

Abstract

A recent paper, Phys. Rev. Research 8, 013261 (2026), claims that the polaromechanical normal-mode splitting (NMS) measured in Nat. Commun. 16, 5652 (2025) is not true based on their two results: $i$) there is no true splitting in the linear-scale spectrum; $ii$) the total or intrinsic decay rate of the cavity-magnon polariton, set by the imaginary part of the pole of the total output spectrum, remains unchanged under the coherent-perfect-absorption (CPA) condition. In this comment, we indicate that $i$) there is NMS in both the linear and logarithmic scales of our spectra in {\it a narrow frequency range} around the CPA frequency; $ii$) the total decay rate defined via the {\it pole} of the spectrum cannot characterize the vanishing {\it effective} decay rate at the CPA frequency (known as the monochromaticity of the CPA), and thus this parameter is irrelevant to the NMS measured in our experiment in {\it a narrow frequency range} around the CPA frequency. Consequently, their results above are either false or irrelevant, and thus cannot support their claim on the polaromechanical strong coupling measured in our experiment.