Effects due to the local fields and the phonons in atomic Bose-Einstein condensates: polariton approach

Summary form only given. The observation of atomic Bose-Einstein condensates (BECs) in magnetic and optical traps has stimulated theoretical investigation of the optical properties of these systems. Many of the current theories are based on the Heisenberg equations of motion for the radiation field and matter. These equations are nonlinear in the field operators and lead to an infinite hierarchy of equations for the atomic correlation functions. The hierarchy can be decoupled using an approximation. In an alternative development, the Heisenberg equations of motion have been simplified using an adiabatic approximation to eliminate the excited-state field operator. While some previous studies of BECs have employed the polariton approach, in these treatments neither the local field effects nor the polariton-phonon coupling are taken into account. Local field effects play an important role in a dense Bose gas (/spl rho//sup I/3//spl lambda//spl Lt/1) where, due to the resonance dipole-dipole interaction,the atoms respond to the electromagnetic field in a collective manner.In this contribution we examine the effects of both the local field and phonons using the polariton approach. The analysis is based on the quasiparticle concept.