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Journal of Physics B Atomic Molecular and Optical Physics

Effect of a dark state on the entanglement of the two-mode field from a laser-driven Λ-type atom

Zhao-Hong Tang, Gao‐xiang Li

Published Jul 23, 2012• 2 citations
Publisher

Abstract

The effect of a dark state on the entanglement properties of the two-mode field from a laser-driven Λ-type three-level atomic system is investigated by taking into account the spontaneously generated coherence (SGC). When the dark state is present, it is found that the entanglement between the two cavity modes can be significantly enhanced compared to the case without the dark state. When the value of SGC is maximal, the dark state population depending on the initial values of the system can affect the entanglement dramatically. Moreover, the effects of a squeezed parameter and Rabi frequency on entanglement evolution are also presented in the presence of a dark state.

DOI
10.1088/0953-4075/45/16/165501

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The effect of a dark state on the entanglement properties of the two-mode field from a laser-driven Λ-type three-level atomic system is investigated by taking into account the spontaneously generated coherence (SGC). When the dark state is present, it is found that the entanglement between the two cavity modes can be significantly enhanced compared to the case without the dark state. When the value of SGC is maximal, the dark state population depending on the initial values of the system can affect the entanglement dramatically. Moreover, the effects of a squeezed parameter and Rabi frequency on entanglement evolution are also presented in the presence of a dark state.
The entanglement properties of two-mode field from a laser-driven collective three-level atomic system are investigated by taking into account the spontaneously generated coherence. Under some conditions, it is found that the entanglement between the two cavity modes can be significantly enhanced by the collectivity of the atoms compared to the case of independent atoms when the relative phase $\ensuremath{\Delta}\ensuremath{\varphi}=\ensuremath{\pi}$. Moreover, the spontaneously generated coherence can also greatly enhance the entanglement in comparison to the case without this coherence.
Abstract Owing to interference induced by spontaneous emission, the density-matrix equations in a three-level Λ-type system have an additional coherence term, which plays a critical role in modulating the inversionless gain and electromagnetically induced transparency effect. In addition, it is shown that spontaneously generated coherence (SGC) has an effect on the entanglement between an atom and a photon of the coupling laser field by calculating the degree of entanglement (DEM) of the atomic system. In this paper, we investigate the influence of the SGC effect on atom-photon entanglement in a Λ-type system, which generally remains a high entangled state. When an incoherent pump source is introduced, we find that the SGC effect could exert considerable influence on the atom reduced entropy under certain conditions for both transient and steady states. More interestingly, such an incoherent pump field could actively affect the short-time dynamic behaviors of the transient quantum entangled state at a certain range of pump rate as a typical coherent case.
The entanglement between a ?-type three-level atom and its spontaneous emission fields is investigated. The effect of spontaneously generated coherence (SGC) on entanglement between the atom and its spontaneous emission fields is then discussed. We find that in the presence of SGC the entanglement between the atom and its spontaneous emission fields is completely phase dependent, while in absence of this coherence the phase dependence of the entanglement disappears. Moreover, the degree of entanglement dramatically changes by the coherent superposition of the atomic states.
We investigate the generation of two-mode-entangled light from a laser-driven three-level $\mathbsf{V}$-type atom inside a cavity by taking into account spontaneously generated quantum interference between two atomic decay channels. We show that under some conditions, the system can reduce to a nondegenerate parametric amplifier which is responsible for the entanglement between the two cavity modes. Compared to the case without the quantum interference, it is found that the entanglement of the cavity field can be significantly enhanced by the interference when the relative phase of the two pumping lasers $\ensuremath{\delta}\ensuremath{\phi}=\ensuremath{\pi}$.
It is shown that the response of a three-level atom interacting with an optical field in a ''dark state geometry'' (single field, degenerate ground states) depends critically on whether or not spontaneously generated coherence (SGC) is present. In the absence of SGC, the system evolves to a dark state. With SGC present, the dark state population is a constant of the motion and the steady-state values for density-matrix elements depend on their initial values at the time the field is applied.
We investigate the evolution of the atomic quantum entropy and the atom–field entanglement in a system of a Λ-configuration three-level atom interacting with a two-mode field with additional forms of nonlinearities of both the field and the intensity-dependent atom–field coupling. With the derivation of the unitary operator within the frame of the dressed state and the exact results for the state of the system we perform a careful investigation of the temporal evolution of the entropy. A factorization of the initial density operator is assumed, considering the field to be initially in a non-correlated two-mode squeezed coherent or binomial state. The effects of the mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy are analysed.