Two-polariton interference phenomenon in dispersive and photonic band-gap materials

Two-polariton spontaneous emission is studied in dispersive and photonic band-gap materials doped with a three-level atom in the cascade configuration. It is found that when the two resonance frequencies of the top and middle excited states of the atom lie outside the band gap, an emission of two polaritons can cause an interference effect. If on the other hand, the resonance frequency of the top state lies within the band gap and the resonance frequency of the middle state lies either within the band gap or outside the band gap, emission of both polaritons is forbidden and no interference effect should be observed.