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arXiv:1805.05831

Maximal atom-photon entanglement in an N-type atomic system

Seyedeh Hamideh Kazemi, Nayyere Einali Saghavaz, Mohammad Mahmoudi

Published May 12, 2018• 0 citations
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Abstract

Atom-photon entanglement provides an essential resource for quantum communication and quantum computation. How to conveniently and efficiently achieve a maximal entanglement between atomic system and spontaneous emission field has been a challenging task. Here, we present a simple, yet we believe a powerful, method to generate entangled states between photons and an N-type atomic system. Beside the achievement of a nearly perfect entanglement, we also examine evidence for a link between entanglement and populations in dressed and bare states; It is found that a maximal entanglement can be established when populations in both dressed and bare states are spread over states. Moreover, the system would be disentangled in the absence of evenly distributed populations, another reason for further strengthen our claim that the physical origin of such entanglement is quantum correlation produced by distribution of the populations. We then discuss the dependence of the entanglement on Rabi frequency and detuning of the applied fields and demonstrate how an almost complete entanglement can be achieved for a judicious choice of these parameters. Note that entanglement is measured in semi-classical regime and by solving density matrix equations of motion and von-Neumann entropy.

DOI
10.48550/arxiv.1805.05831

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Atom-photon entanglement provides an essential resource for quantum communication and quantum computation. How to conveniently and efficiently achieve a maximal entanglement between atomic system and spontaneous emission field has been a challenging task. Here, we present a simple, yet we believe a powerful, method to generate entangled states between photons and an N-type atomic system. Beside the achievement of a nearly perfect entanglement, we also examine evidence for a link between entanglement and populations in dressed and bare states; It is found that a maximal entanglement can be established when populations in both dressed and bare states are spread over states. Moreover, the system would be disentangled in the absence of evenly distributed populations, another reason for further strengthen our claim that the physical origin of such entanglement is quantum correlation produced by distribution of the populations. We then discuss the dependence of the entanglement on Rabi frequency and detuning of the applied fields and demonstrate how an almost complete entanglement can be achieved for a judicious choice of these parameters. Note that entanglement is measured in semi-classical regime and by solving density matrix equations of motion and von-Neumann entropy.
The atom-photon entanglement of dressed atom and its spontaneous emission in a Double-Lambda closed-loop atomic system is studied in multi-photon resonance condition. It is shown that, even in the absence of quantum interference due to the spontaneous emission, the von Neumann entropy is phase-sensitive and it can be controlled by either intensity or relative phase of the applied fields. It is demonstrated that, for the special case of Rabi frequency of the applied fields the system is maximally entangled. Moreover, the open-loop configuration is considered and it is shown that the degree of entanglement measure (DEM) can be controlled by intensity of the applied fields. Furthermore, in electromagnetically induced transparency condition, the system is disentangled. Such a system can be used for quantum information processing via entanglement using optical switching.
The dynamical behavior of entanglement between the atomic ensemble and the spontaneous emission is investigated by applying the femtosecond Gaussian pulses in double- lambda quantum system. In fact by solving the density matrix equations of motion in such a system and by using the von Neumann entropy, the degree of entanglement (DEM) could be measured in semi classical regime and in the multi-photon resonance condition. We interested in investigating the maximum value for DEM and controlled the DEM via relative phase. At first we consider three laser fields as CW optical laser fields and one femtosecond Gaussian field. In this case DEM has interesting behavior. When the system is applied by the other laser fields and Gaussian pulse is still there DEM can be controlled via phase but after finishing the time duration of the femtosecond Gaussian pulse DEM will be phase independent. Then we consider all the laser fields as femtosecond Gaussian pulses which interact with atomic system and we achieve to this point that the steady state entanglement can be occurred by using such ultra-short laser pulses; in this situation DEM will be phase independent. The system would be disentangled in special parameters of Rabi frequencies and all the atoms are coherently populated in a dark state in dressed state picture. Moreover when the system is entangled, there is a population distribution of the atoms in dressed states.
Quantum entanglement provides an essential resource for quantum computation, quantum communication, and quantum network. How to conveniently and efficiently produce entanglement between bright light beams presents a challenging task to build realistic quantum information processing networks. Here, we present an efficient and convenient way to realize a novel quantum phenomenon, named electromagnetically induced entanglement, in the conventional Λ-type three-level atomic system driven by a strong pump field and a relatively weak probe field. Nearly perfect entanglement between the two fields can be achieved with a low coherence decay rate between the two lower levels, high pump-field intensity, and large optical depth of the atomic ensemble. The physical origin is quantum coherence between the lower doublet produced by the pump and probe fields, similar to the well-known electromagnetically induced transparency. This method would greatly facilitate the generation of nondegenerate narrow-band continuous-variable entanglement between bright light beams by using only coherent laser fields, and may find potential and broad applications in realistic quantum information processing.
We propose a scheme that is able to generate on demand a steady-state entanglement between two nondegenerate cavity modes. The scheme relies on the interaction of the cavity modes with driven two- or three-level atoms, which act as a coupler to build entanglement between the modes. We show that, in the limit of a strong driving, it is crucial for the generation of entanglement between the modes to imbalance populations of the dressed states of the driven atomic transition. In the case of a three-level VVV-type atom, we find that a stationary entanglement can be created on demand by tuning the Rabi frequency of the driving field to the difference between the atomic transition frequencies. The resulting degeneracy of the energy levels, together with the spontaneously generated coherence, generate a steady-state entanglement between the cavity modes. It is shown that the condition for the maximal entanglement coincides with the collapse of the atomic system into a pure trapping state. We also show that the creation of entanglement depends strongly on the mutual polarization of the transition atomic dipole moments.
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.
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.