Planar wave beams in bose-einstein condensate

The paper discusses propagation of optical beams through a Bose-Einstein condensate. With the help of numerical simulation shows that the optical beam is focused or defocused depending on the sign of the detuning of the laser frequency from the atomic transition frequency. Established analytical and numerical models describing the evolution of a wave beam in the BEC. For was based on the semiclassical model, in which the condensate is considered from the quantum point of view, and the wave beam classic. This model allows to take into account not only the changes of the wave beam, but also changes in the wave functions of the condensate. The paper considers two models: taking into account spontaneous emission and without. BEC behaves as a medium with the Kerr nonlinearity, the sign of which depends on the sign of the detuning from the resonance frequency. For negative detuning there is a trend towards the focusing of the beam, while for positive detuning there is a defocusing. The wave function of the ground state BEC does not undergo significant changes, while the wave function of the excited state performs oscillations (in the case of resonance with the Rabi frequency). In addition to storing the total number of atoms in the system is the law of conservation of energy for the entire system. The reduction in beam energy leads to the growth of the population of the excited level, and a reduction of the population of the excited level, respectively, leads to an increase in beam energy. For a wide beam in the case of a positive detuning from the resonance is observed in its cleavage.