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arXiv:quant-ph/0604134 · Physical Review A

Experimental continuous-variable entanglement from a phase-difference-locked optical parametric oscillator

Jietai Jing, Sheng Feng, Russell Bloomer, Olivier Pfister

Published Oct 16, 2006• 88 citations
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Abstract

We observed continuous-variable entanglement between the bright beams emitted above threshold by an ultrastable optical parametric oscillator (OPO), classically phase locked at a frequency difference of $161.827\phantom{\rule{0.2em}{0ex}}324\phantom{\rule{0.2em}{0ex}}0(5)\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. The amplitude-difference squeezing is $\ensuremath{-}3\phantom{\rule{0.3em}{0ex}}\mathrm{dB}$ and the phase-sum one is $\ensuremath{-}1.35\phantom{\rule{0.3em}{0ex}}\mathrm{dB}$. Besides proving entanglement in a phase-locked OPO, such outstanding frequency-difference stability paves the way for transferring entanglement between different optical frequencies and densely implementing continuous-variable quantum information in the frequency domain.

DOI
10.1103/physreva.74.041804

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We observed continuous-variable entanglement between the bright beams emitted above threshold by an ultrastable optical parametric oscillator (OPO), classically phase locked at a frequency difference of 161.8273240(5)MHz161.827\phantom{\rule{0.2em}{0ex}}324\phantom{\rule{0.2em}{0ex}}0(5)\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}161.8273240(5)MHz. The amplitude-difference squeezing is \ensuremath−3dB\ensuremath{-}3\phantom{\rule{0.3em}{0ex}}\mathrm{dB}\ensuremath−3dB and the phase-sum one is \ensuremath−1.35dB\ensuremath{-}1.35\phantom{\rule{0.3em}{0ex}}\mathrm{dB}\ensuremath−1.35dB. Besides proving entanglement in a phase-locked OPO, such outstanding frequency-difference stability paves the way for transferring entanglement between different optical frequencies and densely implementing continuous-variable quantum information in the frequency domain.
We observed continuous-variable entanglement between two bright beams emitted above threshold by a phase-difference-locked ultrastable optical parametric oscillator. The amplitude-difference squeezing is -3 dB and the phase-sum one is -1.35 dB. The beams are classically phase-locked at a frequency difference of 161.8273240(5) MHz, continuously tunable by the OPO crystal temperature. Such unprecedented frequency-difference stability paves the way for implementing quantum frequency multiplexing and CV quantum information in the frequency domain.
We report the realization of a classically phase-locked source of quantum twin beams. Theoretical work by Reid and Drummond, and more recently by van Loock and Braunstein, predicts that such a source is adequate for creating bipartite and multipartite continuous-variable entanglement. The source is a type-II optical parametric oscillator (OPO) above threshold. Its exceptional frequency and intensity stability is derived from careful design and from three servo loops. The OPO can stably emit on the frequency-degenerate mode, pumped a few percent above the threshold. We observe a preliminary number-difference squeezing of 5.5 dB (6.4 dB inferred) at 200 kHz. In order to enable future EPR measurements, the signal and idler fields must also be classically phase-locked: we measure a signal-idler-frequency-difference linewidth smaller than 300 Hz for our OPO.
We present the first measurement of squeezed-state entanglement between the twin beams produced in an optical parametric oscillator operating above threshold. In addition to the usual squeezing in the intensity difference between the twin beams, we have measured squeezing in the sum of phase quadratures. Our scheme enables us to measure such phase anticorrelations between fields of different frequencies. In the present measurements, wavelengths differ by approximately 1 nm. Entanglement is demonstrated according to the Duan et al. criterion [Phys. Rev. Lett. 84, 2722 (2000)] Delta2p- + Delta2q+ = 1.41(2) < 2. This experiment opens the way for new potential applications such as the transfer of quantum information between different parts of the electromagnetic spectrum.
We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam splitter to convert number-difference squeezing into phase-difference squeezing, and thus provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.