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arXiv:1003.1357 · Optics Letters

Continuous variable entanglement enhancement and manipulation by a subthreshold Type II optical parametric amplifier

Yana Shang, Xiaojun Jia, Yumei Shen, Changde Xie, Kunchi Peng

Published Mar 12, 2010• 28 citations
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Abstract

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.

DOI
10.1364/ol.35.000853

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We experimentally demonstrated that the quantum correlations of amplitude and phase quadratures between signal and idler beams produced from a non-degenerate optical parametric amplifier (NOPA) can be significantly improved by using a mode cleaner in the pump field and reducing the phase fluctuations in phase locking systems. Based on the two technical improvements the quantum entanglement measured with a two-mode homodyne detector is enhanced from approximately 4 dB to approximately 6 dB below the quantum noise limit using the same NOPA and nonlinear crystal.
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.
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Quantum fluctuations in a nondegenerate optical parametric amplifier (NOPA) are investigated experimentally with a squeezed state coupled into the internal idler mode of the NOPA. Reductions of the inherent quantum noise of the amplifier are observed with a minimum noise level 0.7 dB below the usual noise level of the amplifier with its idler mode in a vacuum state. With two correlated quantum fields as the amplifier's inputs and proper adjustment of the gain of the amplifier, it is shown that the amplifier's intrinsic quantum noise can be completely suppressed so that noise-free amplification is achieved. It is also shown that the NOPA, when coupled to either a squeezed state or a nonclassically correlated state, can realize quantum tapping of optical information.
In this paper, we propose a scheme to produce a multiplexed entanglement frequency comb in a type II phase-matching nondegenerate optical parametric amplifier (NOPA) operating below threshold. The entanglement of the signal and idler frequency combs in the wide frequency range, which is limited by the phase-matching bandwidth of the NOPA, is investigated by the inseparability criterion. Furthermore, N Einstein–Podolsky–Rosen pairs can be created from the two combs without any reduction in the correlations by using frequency-dependent beam splitters.