Beyond single-photon localization at the edge of a photonic band gap - art. no. 053812

We study spontaneous emission in an atomic ladder system, with both transit ions coupled near resonantly to the edge of a photonic band gap continuum. The problem is solved through a recently developed technique and leads to t he formation of a two-photon + atom bound state with fractional population trapping in both upper states. In the long-time limit, the atom can be foun d excited in a superposition of the upper states and a direct two-photon pr ocess coexists with the stepwise one. The sensitivity of the effect to the particular form of the density of states is also explored.