As a result, the bright state couples collectively to |G, 1⟩ with a coupling strength √ N g where g is the coupling between |E J , 0⟩ and |G, 1⟩. Notably, the |D k , 0⟩ states do not couple to the |G, 1⟩ state, and thus are referred to as the dark states. The coupling √ N g leads to the formation of the |+⟩ (upper polariton) and |-⟩ (lower polariton) states that are linear combinations of |G, 1⟩ and |B, 0⟩ (see more in Eq. 12 and onward) as depicted in Fig. .