Study on spontaneous emission from two or more atoms and the role of entanglement

Abstract

In this paper we investigate several phenomena related to spontaneous emission from two or more atoms and the role of entanglement in them. For this we introduce the atom-field interaction Hamiltonian and use two approaches, the Schr\"{o}dinger equation approach and the master equation approach. When the atoms are separated by small distances($R \ll \lambda$), cooperative spontaneous emission occures, leading to such phenomena as superradiance, subradiance and photon(population) trapping. These are induced by the resonance dipole-dipole interaction and we can understand them by considering the time evolution of populations of the symmetric state and the antisymmetric state. When the atoms are separated by large distances($R \gg \lambda$), the atoms may be considered to emit photons independently of one another. Nevertheless, photons emitted from different atoms can exhibit interesting directional properties. This is induced by the constructive interference and destructive interference of the emitted photons and we can understand it by considering the initial or intermediate entanglement of the atomic system. We consider two- and three-atom spontaneous emission processes in detail by using a full quantum mechanical treatment.