The strange attraction phenomenon in cQED: The intermediate quantum coupling regime. S. Echeverri-Arteaga, H. Vinck-Posada and E. Gómez in Optik 183:389 (2019).  What the paper says!?

This is a follow-up paper from their previous work for which the same griefs expressed there apply here (namely, they ignore our collaboration on similar topics.

Here, instead of a spectral triplet, they focus on the observation by T. Tawara et al. of attractions between the polaritons at resonance. Although the later work by J. Huang et al. quoting them for the new "intermediate coupling" regime they analyze, discards frequency pulling as something else, here they say that it's further evidence of the same thing.

Their Liouvillian:

It is interesting to note that in a previous experimental work on a single QD coupled to a PhCC under resonant excitation, a simple phonon dephasing model was investigated and suggested that this theoretical approach could be useful for describing the off-resonant QD-cavity in-

teraction [17,18].

They neglect the other term:

They make interesting connections of $P_\theta$ to temperature and other microscopic assumptions (cf. their Eq. (2)).

In Section 2, they detail the "Lindblad master equation approach without gain" (only keeping one term in the Lindblad, no pumping, decay as imaginary part in Hamiltonian).

Their discussion of the coexistence:

When the phonon-mediated coupling is in the range $P_\theta^{(2)} < P_\theta < P_\theta^{(1)}$, the emission properties of the system will be characterized by the presence of the Rabi splitting of the first rung (lower than 2g), as a remainder of the strong coupling regime, and a singlet that clearly blueshift toward the exciton resonance. This blueshift is an immediate consequence of the DPT in the system, where characteristics of strong and weak coupling regimes are shared simultaneously. This phenomenology can be coined as the quantum intermediate coupling regime in agreement with the hy-

pothesis of Tawara's work.

On the interpretation of the results:

The emission peak C and X cannot be associated with the bared cavity and the QD, since the system do not operates in a genuine weak coupling regime. Instead of this, the system is in an intermediate quantum regime where the apparent crossing observed is the result of the formation of a resonance state. Hence, the emission peak C corresponds to a collective emission from all rungs in the JC ladder near to the cavity

frequency and the emission peak X is due to optical transitions from the two polaritons of the first rung.

Despite the disappointment of their unfair treatment in their citations (we are not cited at all), this seems to be a nice work, worthy of more attention.