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Chinese Physics Letters

Entanglement Enhancement Via Collective CPT in Bichromatically Driven Three-Level Atoms

Huatang Tan, Wenwu Deng

Published Sep 1, 2009• 2 citations
Publisher

Abstract

We investigate the generation of two-mode entangled light from cooperative three-level cascade emitters driven by two lasers inside an optical cavity. It is found that through collective coherent population trapping (CPT) to prepare the atomic states close to the coherent superposition state |1 > — |3>/√22 of the top and ground levels, the entanglement and mean photon number of the entangled light can be significantly enhanced in comparison to the case of independent atoms.

DOI
10.1088/0256-307x/26/9/094205

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We investigate the generation of two-mode entangled light from cooperative three-level cascade emitters driven by two lasers inside an optical cavity. It is found that through collective coherent population trapping (CPT) to prepare the atomic states close to the coherent superposition state |1 > — |3>/√22 of the top and ground levels, the entanglement and mean photon number of the entangled light can be significantly enhanced in comparison to the case of independent atoms.
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.
We explore the quantum entanglement between two collective fields via atomic coherence effects. For three-level atoms in V\mathsf{V}V configuration driven by two applied fields on two-photon resonance, one coherent superposition of the excited states is not excited, which is the counterpart of coherent population trapping. The coherence-induced depopulation makes two cavity fields in each collection combine into a quantum-beat, i.e., equivalently, the difference mode of the two components decouples from the driven atoms. The two sum modes, when they are arranged in the four-wave mixinglike interactions, can be prepared in Einstein-Podolsky-Rosen entangled state. Correspondingly, any two individual fields from different collective modes are entangled with each other. Furthermore, the effects of thermal reservoir and laser linewidths are discussed, and a generalization is given to the case in which each quantum beat involves more than two modes.
We consider a three-level cascade laser in which a coherently driven non-degenerate three-level atom available in a closed cavity coupled to a twomode vacuum reservoir.Applying the interaction Hamiltonian and Heisenberg equation of motion, we analyze the mean photon number, quadrature squeezing, and entanglement properties of the light produced by this quantum optical system inside the cavity.We find that the light generated by this system is in a two-mode squeezed state under certain conditions and the state of the system is weakly entangled at steady state due to the presence of the two-mode vacuum reservoir noise.
We study a nondegenerate three-level cascade laser coupled to a two-mode vacuum reservoir, by employing the stochastic differential equations associated with the normal ordering. The amplification of the properties of squeezing and entanglement of the cavity light is investigated. We have found that there is an entanglement between the states of the light generated in the cavity, due to the strong correlation of the light emitted, when the atom decays from the top level to the bottom level via the intermediate one. We have also obtained that the two cavity modes are strongly entangled, and the degree of entanglement is directly related to the two-mode squeezing.
Squeezing and entanglement of a two-mode cascade laser, produced by a three-level atom which is initially prepared by a coherent superposition of the top and bottom levels then injected into a cavity coupled to a two-mode squeezed vacuum reservoir is discussed. I obtain stochastic differential equations associated with the normal ordering using the pertinent master equation. Making use of the solutions of the resulting differential equations, we determined the mean photon number for the cavity mode and their correlation, EPR variables, smallest eigenvalue of the symplectic matrix, intensity difference fluctuation, and photon number correlation. It is found that the squeezed vacuum reservoir increases the degree of the statistical and nonclassical features of light produced by the system. Furthermore, using the criteria developed by logarithm negativity and Hillery-Zubairy criteria, the quantum entanglement of the cavity mode is quantified. It is found that the degree of the entanglement for the system under consideration increases with the squeezing parameter of the squeezed vacuum reservoir.