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Journal of Physics B Atomic Molecular and Optical Physics

Enhanced continuous-variable entanglement by a self-phase-locked type-II optical parameter oscillator with feedback loops

Yonghong Ma, Qing-Xia Mu, Guo-Hui Yang, Ling Zhou

Published Oct 13, 2008• 30 citations
Publisher

Abstract

We consider a three-level cascade laser with a self-phase-locked type-II nondegenerate optical parameter oscillator via a homodyne-mediate quantum feedback. Applying the pertinent master equation, we investigate the squeezing, entanglement properties and the mean photon number produced by our system. It is found that highly squeezed and macroscopic entangled light with high intensity can be generated.

DOI
10.1088/0953-4075/41/21/215502

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We consider a three-level cascade laser with a self-phase-locked type-II nondegenerate optical parameter oscillator via a homodyne-mediate quantum feedback. Applying the pertinent master equation, we investigate the squeezing, entanglement properties and the mean photon number produced by our system. It is found that highly squeezed and macroscopic entangled light with high intensity can be generated.
We investigate the enhancement of the intracavity entanglement of a self-phase-locked type-II nondegenerate optical parameter oscillator (SPL NOPO) via homodyne-mediated quantum feedback. It is found that the feedback can effectively enhance the squeezing, entanglement, and purity of the two-mode field in the SPL NOPO. Especially for an ordinary NOPO, our feedback scheme can simulate a standard two-mode squeezed vacuum environment and a pure steady two-mode squeezed vacuum cavity field can be generated, different from the scheme proposed by Mancini [Phys. Rev. A 73, 010304(R) (2006)] in which only a mixed two-mode entangled state is generated.
We consider a nondegenerate three-level cascade laser with a subthreshold nondegenerate parametric oscillator coupled to a vacuum reservoir. Applying the pertinent master equation, we analyze the squeezing and entanglement properties of the two-mode light produced by this quantum optical system inside and outside the cavity. We also determine the normalized second-order correlation function for the two-mode light as well as for individual mode. We find that the light generated by this system is in a two-mode squeezed state and the state of the system is strongly entangled at steady state. Moreover, the presence of the parametric oscillator leads to an increase in the degree of squeezing and entanglement. We also find that the intermode correlation decreases as the injected atomic coherence decreases in the system.
We discuss the evolution of two-mode states of a self-phase-locked type-II nondegenerate optical parametric oscillator with homodyne-mediated quantum feedback. It is shown that different strengths of the feedback loops can simulate the effect of a squeezed thermal environment and lead additionally to the process of the parametric-down conversion for each mode. In the steady state regime all initial density matrices evolve towards a Gaussian equilibrium state. It is shown that the nonsymmetric feedback can further increase entanglement of the equilibrium state. Dynamical behaviour of intracavity entanglement for a number of initial states is investigated, and entanglement sudden death and birth phenomena, and a delay birth of entanglement are reported.
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.