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The Journal of Atomic and Molecular Sciences

Spontaneous Emission Induced Entanglement and Steady Entanglement in Two Atomic System

Hui-Yun Xu, Yang Guohui

Published Mar 2, 2016• 0 citations
Publisher

Abstract

We report possibility of generating entanglement between two atoms in free space when their spatial separation is on the order of wavelength or less. We show that these two atoms get coupled by photon exchange due to spontaneous decay, which in turn generates the atomic entanglement. By introducing the incoherent pumping, one can obtain the steady entanglement, and the incoherent pumping can overcome the decay of the atoms. Moreover, one can obtain the larger value of steady entanglement via proper tuning the incoherent pumping.

DOI
10.4208/jams.101515.112015a

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We report possibility of generating entanglement between two atoms in free space when their spatial separation is on the order of wavelength or less. We show that these two atoms get coupled by photon exchange due to spontaneous decay, which in turn generates the atomic entanglement. By introducing the incoherent pumping, one can obtain the steady entanglement, and the incoherent pumping can overcome the decay of the atoms. Moreover, one can obtain the larger value of steady entanglement via proper tuning the incoherent pumping.
We report on the generation of entanglement between two spatially separated identical atoms in free space. We show that the evolution of the entanglement occurs due to the radiative coupling between the two atoms via the retarded dipole-dipole interaction. The magnitude of the entanglement is found to be strongly dependent on the initial states and the distance between the two atoms. We also study the different effects on the entanglement of the dipole-dipole collective parameters in the master equation. By introducing incoherent pumping, a steady entanglement can be acquired, and the condition for generating steady entanglement is also obtained.
We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited-state lifetime and radiative coupling strength between the two atoms. We demonstrate that steady-state SGE can be established by incoherently pumping the atoms to their excited states. We have shown that an appropriate rate of incoherent pump can help in producing optimal steady-state SGE. The multilevel systems offer us more channels to establish entanglement. The system under consideration can be realized in a tight trap or atoms/ions doped in a solid substrate.
In this paper we explore the possibility of a steady-state entanglement of two two-level atoms inside a pumped cavity by taking into account cavity leakage and the spontaneous emission of photons by the atoms. We describe the system in the dressed state picture in which the coherence is built into the dressed states while transitions between the dressed states are incoherent. Our model assumes the vacuum Rabi splitting of the dressed states to be much larger than any of the decay parameters of the system which allows atom-field coherence to build up before any decay process takes over. We show that, under our model, a pumping field cannot entangle two closed two-level atoms inside the cavity in the steady-state, but a steady-state entanglement can be achieved with two open two-level atoms.
In contrast to the general argument that the spontaneous decay is intrinsically incoherent in nature and detrimental to quantum entanglement, here, we show that nearly perfect entanglement between two bright pump fields can be realized via spontaneous decay-induced destructive quantum interference in a closed double Lambda-type four-level atomic system with the energy separation of the excited doublet comparable to their decay rates. The high degree of bipartite entanglement results from the cancellation of spontaneous emission and subsequent elimination of the associated noise due to the destructive quantum interference between the two spontaneous emission pathways from the upper doublet to each of the two lower levels when the two strong pump fields are tuned to the particular frequencies where quantum interference takes place. This scheme is particularly suitable for the generation of entanglement between two bright light fields, and may find potential applications in realistic quantum information processing.
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 role of the collective antisymmetric state in entanglement creation by spontaneous emission in a system of two non-overlapping two-level atoms has been investigated. Populations of the collective atomic states and the Wootters entanglement measure (concurrence) for two sets of initial atomic conditions are calculated and illustrated graphically. Calculations include the dipole-dipole interaction and a spatial separation between the atoms that the antisymmetric state of the system is included throughout even for small interatomic separations. It is shown that spontaneous emission can lead to a transient entanglement between the atoms even if the atoms were prepared initially in an unentangled state. It is found that the ability of spontaneous emission to create transient entanglement relies on the absence of population in the collective symmetric state of the system. For the initial state of only one atom excited, entanglement builds up rapidly in time and reaches a maximum for parameter values corresponding roughly to zero population in the symmetric state. On the other hand, for the initial condition of both atoms excited, the atoms remain unentangled until the symmetric state is depopulated. A simple physical interpretation of these results is given in terms of the diagonal states of the density matrix of the system. We also study entanglement creation in a system of two non-identical atoms of different transition frequencies. It is found that the entanglement between the atoms can be enhanced compared to that for identical atoms, and can decay with two different time scales resulting from the coherent transfer of the population from the symmetric to the antisymmetric state. In addition, it was found that a decaying initial entanglement between the atoms can display a revival behaviour.