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arXiv:0709.2237

An efficient source of continuous variable polarisation entanglement

Ruifang Dong, J. Heersink, Jun–ichi Yoshikawa, O. Glöckl, Ulrik L. Andersen, Gerd Leuchs

Published Sep 14, 2007• 1 citation
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Abstract

We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarisation states. Exploiting an optimised scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarisation squeezed pulses with a mean classical excitation in S3. Polarisation entanglement was generated by interfering two independent polarisation squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark S1 - S2 polarisation plane. To verify entanglement generation, we characterised the quantum correlations of the system for two different sets of conjugate Stokes parameters. The quantum correlations along the squeezed and the anti-squeezed Stokes parameters were observed to be -4.1 +/- 0.3 dB and -2.6 +/- 0.3 dB below the shot noise level respectively. The degree of correlations was found to depend critically on the beam splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of -3.6 +/- 0.3 dB and -3.4 +/- 0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam splitter, even in the presence of excess noise.

DOI
10.48550/arxiv.0709.2237

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We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarisation states. Exploiting an optimised scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarisation squeezed pulses with a mean classical excitation in S3. Polarisation entanglement was generated by interfering two independent polarisation squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark S1 - S2 polarisation plane. To verify entanglement generation, we characterised the quantum correlations of the system for two different sets of conjugate Stokes parameters. The quantum correlations along the squeezed and the anti-squeezed Stokes parameters were observed to be -4.1 +/- 0.3 dB and -2.6 +/- 0.3 dB below the shot noise level respectively. The degree of correlations was found to depend critically on the beam splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of -3.6 +/- 0.3 dB and -3.4 +/- 0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam splitter, even in the presence of excess noise.
We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarization states. Exploiting an optimized scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with a mean classical excitation in . Polarization entanglement was generated by interfering two independent polarization squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark polarization plane. To verify entanglement generation, we characterized the quantum correlations of the system for two different sets of conjugate Stokes parameters. The quantum correlations along the squeezed and the anti-squeezed Stokes parameters were observed to be −4.1±0.3 and −2.6±0.3 dB below the shot noise level, respectively. The degree of correlations was found to depend critically on the beam-splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of −3.6±0.3 and −3.4±0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam splitter, even in the presence of excess noise.
We have experimentally demonstrated polarization entanglement using continuous variables in an ultra-short pulsed laser system at the telecommunications wavelength of 1.5µm. Exploiting the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with Ŝ 2 as the only non-zero Stokes parameter, thus Ŝ 1 and Ŝ 3 being the conjugate pair. Polarization entanglement was generated by interference of the polarization squeezed field with a vacuum on a 50:50 beamsplitter. The two resultant beams exhibit strong quantum noise correlations in Ŝ 1 and Ŝ 3 . The sum noise signal of Ŝ 3 was at the respective shot noise level and the difference noise signal of Ŝ 1 fell −2.9 dB below this value.
Photonic crystal fibres (PCF) can be tailored to introduce a high effective nonlinear Kerr effect and to create lower amounts of excess noise compared to standard fibres. By exploiting both polarisation axes of the polarisation maintaining PCF we can generate two independent polarisation squeezed beams that can be used to create polarisation entanglement. We generated a maximum squeezing of-3.9 Aring plusmn 0.3 dB and a corresponding anti-squeezing of 16.8 Aring plusmn 0.3 dB. Furthermore we investigate the generation of polarisation squeezing in photonic crystal fibres by using a single pass setup where both the slow and fast axis has to be utilized. Taking advantage of these features and using ultrashort pulses we create polarisation squeezed states with notably higher purity than obtained in standard fibres.
We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0+/-0.2 (4.0+/-0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80+/-0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64+/-0.08) is well below the EPR limit of unity.
We experimentally demonstrate the production of continuous variable entanglement of femto second laser pulses from an all-fibre asymmetric Sagnac interferometer exploiting the Kerr effect. Contrary to the experiment of Silberhorn et al. [Phys. Rev. Lett. 86, 4267 (2001)], the asymmetric coupler in the Sagnac loop is fully integrated in the fibre, making the source extremely compact, reliable and robust. Employing a simple detection scheme, comprising a beam splitter and two intensity detectors, we clearly observe quantum correlations of conjugate quadratures, hereby witnessing entanglement.