Multiphoton Localization and Propagating Quantum Gap Solitons in a Frequency Gap Medium

The many-particle spectrum of an isotropic frequency gap medium doped with impurity resonance atoms is studied using the Bethe ansatz technique. The spectrum is shown to contain pairs of quantum correlated “gap excitations” and their heavy bound complexes (“gap solitons”), enabling the propagation of quantum information within the classically forbidden gap. In addition, multiparticle localization of the radiation and the medium polarization occurs when such a gap soliton is pinned to the impurity atom.