Studies Of Generation Entangled Radiation Via Coherence Controlled Atomic Reservoir

Quantum entanglement is a correlative and inseparable property among the parts of the quantum systems. That is the non-local correlation, which is the special property of the quantum system. Entanglement is a basic resource of the quantum communication, so the preparation of the entanglement is essential. However, the decoherence would occur among the entangeled states easily, which lead the entanglement to be fragile. So the method of preparating the robust, steady, and high entanglement have been sought to constantly. Since then, there are many experiments to achieve the entanglement. The experiments range from in a correlated state by a radiative process, to exchange a single photons in the cavity, to mediate by a single trapped atom or using the Kerr nonlinearity of an optical fiber, and so on. We are more interesting in atomic coherence effect. Atomic coherence have led to many novel effects such as coherent population trapping(CPT), eletromagnetic-induced transparency, lasing without inversion, and control spontaneous emission. It was shown that Einstein-Podolsky-Rosen(EPR) entanglement of continuous variables or Fock states of light can be generated by using atomic coherence effects, which is feasible and convenient.In this paper, we studied and discovered that the atomic reservoir can be controlled by coherent population trapping(CPT). We could achieve the entanglement by this atomic reservoir. We choose two models of three-level atoms as the reservoir to interact with the two-mode light cavity. A beam of three-level atoms are initially prepared in near CPT state and act as long-lived coherence-controlled reservoir. Four-wave-mixing leads to amplification of cavity modes resonant with Rabi sidebands of the atomic dipole transitions. The cavity modes evolve into EPR state, whose degree of entanglement is controlled by the intensity and the frequencies of the driven fields. This scheme use the long-lived CPT coherence and is robust against spontaneous emission of the atomic beam. Through the dressed transformation, the rotation transformation, the dipole approximation, and choosing the proper conditions and parameters, the robust two-mode entanglement is achieved by one-step procedure.