The relevance of degenerate states in chiral polaritonics.

In this work, we theoretically explore whether a parity-violating/chiral light-matter interaction is required to capture all relevant aspects of chiral polaritonics or if a parity-conserving/achiral theory is sufficient (e.g., long-wavelength/dipole approximation). This question is non-trivial to answer since achiral theories (Hamiltonians) still possess chiral solutions. To elucidate this fundamental theoretical question, a simple GaAs quantum ring model is coupled to an effective chiral mode of a single-handedness optical cavity in dipole approximation. The bare matter GaAs quantum ring possesses a non-degenerate ground state and a doubly degenerate first excited state. The chiral or achiral nature (superpositions) of the degenerate excited states remains undetermined for an isolated matter system. However, inside our parity-conserving description of a chiral cavity, we find that the dressed eigenstates automatically (ab initio) attain chiral character and become energetically discriminated based on the handedness of the cavity. In contrast, the non-degenerate bare matter state (ground state) does not show energetic discrimination inside a chiral cavity within a dipole approximation. Nevertheless, our results suggest that the handedness of the cavity can still be imprinted onto these states (e.g., angular momentum and chiral current densities). Overall, the above findings highlight the relevance of degenerate states in chiral polaritonics. In particular, because recent theoretical results for linearly polarized cavities indicate the formation of a frustrated and highly degenerate electronic ground state under collective strong coupling conditions, which, likewise, is expected to form in chiral polaritonics and, thus, could be prone to chiral symmetry breaking effects.