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arXiv:1201.1159 · Physical Review A

Cascaded entanglement enhancement

Zhihui Yan, Xiaojun Jia, Xiaolong Su, Zhiyuan Duan, Changde Xie, Kunchi Peng

Published Apr 16, 2012• 50 citations
arXivHTMLPDF

Abstract

We present a cascaded system consisting of three nondegenerate optical parametric amplifiers (NOPAs) for the generation and the enhancement of quantum entanglement of continuous variables. The entanglement of optical fields produced by the first NOPA is successively enhanced by the second and the third NOPAs from $\ensuremath{-}5.3$ to $\ensuremath{-}8.1$ dB below the quantum noise limit. The dependence of the enhanced entanglement on the physical parameters of the NOPAs and the reachable entanglement limitation for a given cascaded NOPA system are calculated. The calculation results are in good agreement with the experimental measurements.

DOI
10.1103/physreva.85.040305

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We present a cascaded system consisting of three nondegenerate optical parametric amplifiers (NOPAs) for the generation and the enhancement of quantum entanglement of continuous variables. The entanglement of optical fields produced by the first NOPA is successively enhanced by the second and the third NOPAs from \ensuremath−5.3\ensuremath{-}5.3\ensuremath−5.3 to \ensuremath−8.1\ensuremath{-}8.1\ensuremath−8.1 dB below the quantum noise limit. The dependence of the enhanced entanglement on the physical parameters of the NOPAs and the reachable entanglement limitation for a given cascaded NOPA system are calculated. The calculation results are in good agreement with the experimental measurements.
We experimentally demonstrate that the quantum entanglement between amplitude and phase quadratures of optical modes produced from a nondegenerate optical parametric amplifier (NOPA) can be enhanced and manipulated phase sensitively by means of another NOPA. When both NOPAs operate at deamplification, the entanglement degree is increased at the cavity resonance of the second NOPA. When the first NOPA operates at deamplification and the second one at amplification, the spectral features of the correlation variances are significantly changed. The experimental results are in good agreement with the theoretical expectation.
We consider a system consisting of NNN nondegenerate optical parametric amplifiers (NOPAs) operating below threshold and linked with each other in a cascading way, each taking the output subharmonic fields from the previous one as the input fields. The entanglement properties of the subharmonic fields from these cascading nondegenerate optical parametric amplifiers (CNOPAs) are investigated. We find that, if the input subharmonic fields of the first NOPA in the cascading line are in the vacuum state, the output fields from the later NOPAs exhibit excellent broadband entanglement, and the entanglement frequency band is broadened notably with increased number of cascading NOPAs. We also discuss the application of the entangled light generated from the CNOPAs to broadband teleportation, and find that the maximum width of the fidelity spectrum of teleportation of broadband coherent states can be greatly broadened.
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We demonstrate the enhanced quantum noise reduction of the output field from an optical parametric amplifier (OPA) by employing the cascaded optical parametric amplifiers (COPA), in which the output field of one OPA is the input field of the subsequent one. The output field noise formulas of the cascaded degenerate and nondegenerate OPAs (CDOPA and CNOPA) are obtained. The analytical results show that a CDOPA and a CNOPA can generate squeezing beams and entangled beams with a wider bandwidth under a low pump parameter, respectively. The cavity output efficiency and the intracavity loss are the main factors for improving the degrees of squeezing and entanglement. Our work will provide improved schemes for designing COPAs to efficiently produce high-quality squeezed and entangled states, which have potential applications in quantum-information processing.