Dicke enhancement of light-matter interaction for a single quasi-degenerate multilevel emitter

We study a quantum emitter with N nearly degenerate excited states (sublevels) coupled to the ground state via the same optical resonance. We show that in such circumstances an approximate Jaynes-Cummings system emerges, with an effective coupling constant scaling with the square root of N. While our conclusions hold in general, we also present detailed analytical derivations for the instructive case N=2. Employing a quantum optical master equation we further observe that our system can closely match the spectral line shapes and photon autocorrelation functions typical of Jaynes-Cummings physics. Interestingly, we find that finite emitter dephasing can improve the quality of the approximation in some cases. By showing a novel route to increase the effective light-matter coupling strength, our findings may facilitate the control and detection of single-photon nonlinearities at ambient conditions.