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arXiv:1210.3179 · Journal of Physics B Atomic Molecular and Optical Physics

The effect of a coupling field on the entanglement dynamics of a three-level atom

Ali Mortezapour, Majid Abedi, Mohammad Mahmoudi, M R H Khajehpour

Published Apr 11, 2011• 21 citations
arXivHTMLPDF

Abstract

The effect of a coupling laser field on the entanglement of a three-level quantum system and its spontaneous emission is investigated via the reduced quantum entropy.We consider two schemes: the upper-and lower-level couplings.By calculating the degree of entanglement (DEM) for both systems, it is shown that the entanglement between the atom and its spontaneous emission can be controlled by the coupling laser field.This field, however, affects the entanglement differently in the two schemes; it is only the lower-level coupling scheme that shows a non-zero steady state DEM which can be controlled by the intensity and detuning of the coupling laser field.

DOI
10.1088/0953-4075/44/8/085501

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We study the entanglement of dressed atom and its spontaneous emission in a three-level Λ-type closed-loop atomic system in a multi-photon resonance condition and beyond it. It is shown that the von Neumann entropy in such a system is phase-dependent, and it can be controlled by either the intensity or relative phase of applied fields. It is demonstrated that for the special case of the Rabi frequency of applied fields, the system is disentangled. In addition, we take into account the effect of Doppler broadening on the entanglement and it is found that a suitable choice of laser propagation direction allows us to obtain the steady state degree of entanglement (DEM) even in the presence of the Doppler effect.
The density matrix equations of motion in near-degenerate three-level V-type closed-loop atomic system are calculated numerically in Floquet frame. The dynamical behavior of atom- photon entanglement between the dressed atom and its spontaneous emission is studied in semi classical approach beyond the two-photon resonance condition in such a system. The quantum entropy of these two subsystems is investigated by using the von Neumann entropy. It is shown that, the degree of entanglement measure (DEM) can be controlled via the intensity and the detuning of coupling optical field and quantum interference induced by spontaneous emission. Moreover in the absence of quantum interference the steady state behavior of DEM can be achieved even in beyond the two- photon resonance condition. Furthermore in the absence of quantum interference for special parameters of Rabi frequency and detuning of driving laser field disentanglement can be occurred. Also the electromagnetically induced transparency condition can be obtained when the system is disentangled.
In this research, the disentanglement conditions between the coated atom and its spontaneous emission in double- lambda quantum system was investigated. Initially, the entanglement increased due to the interaction between the laser fields and the four- level atom. This entanglement can be controlled by changing the intensity of the applied fields. By applying the two coupling fields, the system is entangled and the system would be disentangled with one coupling field and one probe field. The present research demonstrated that spontaneous emission by changing the population of atoms in the alignments is a good source of entanglement, but fields were manipulated in such a way that this entanglement was reduced by coherent trapping of the population for the atoms.
The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.
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.
Abstract In this letter, we have proposed a new model for quantum control of atom photon entanglement in a single layer graphene via von Neumann reduced entropy of entanglement. We consider the effect of terahertz laser field intensity on the degree of entanglement (DEM) in the resonance and off-resonance condition of the applied fields. We also investigate the spatially dependent of the DEM when two applied light becomes standing wave pattern in x and y directions. Our results show that in different parametric conditions, the population of the different states can be controlled and this leads to modifying the DEM of the system.