The paper presents a significant, overarching error by failing to account for the detrimental impact of metasurfaces on the quantum properties of the emitted light.
While it extensively documents enhancements in classical metrics like brightness and emission rate, it systematically overlooks how these very nanostructures degrade the essential quantum metrics:
* Plasmonic Decoherence: The use of lossy metallic metasurfaces (e.g., gold nanocubes) for Purcell enhancement is known to cause severe dephasing, broadening emission linewidths and destroying photon indistinguishability—a critical parameter for quantum computing. This is not adequately addressed.
* Fabrication Imperfections: Real-world metasurfaces have imperfections that scatter light and broaden resonances. This directly undermines the spectral purity of photon pairs and the stability of single-photon emission, which the paper ignores in its optimistic assessment.
* Incomplete Quantum Validation: Claims of “high-purity” or “entangled” photon generation are made without consistently reporting the necessary proof, such as second-order correlation functions g^2(0)for purity or Bell inequality violations for entanglement fidelity.
In essence, the review highlights the “gain” in brightness while ignoring the “cost” in quantum coherence. This invalidates its central conclusion that metasurfaces unconditionally lead to superior quantum light sources, as a bright but incoherent source is useless for advanced quantum applications.