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arXiv:quant-ph/0405118 · Physical Review A

Direct measurement and reconstruction of nonclassical features of twin beams generated in spontaneous parametric down-conversion

Ondřej Haderka, Jan Peřina, Martin Hamar, Jan Peřina

Published Mar 24, 2005• 91 citations
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Abstract

Correlations in twin beams composed of many photon pairs are studied using an intensified CCD camera. Joint signal-idler photon-number distribution and quantum phase-space quasidistributions determined from experimental data have nonclassical features.
DOI
10.1103/physreva.71.033815

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Measurement of photon-number statistics of fields composed of photon pairs generated in spontaneous parametric downcoversion pumped by strong ultrashort pulses is described. Final detection quantum efficiencies, noises as well as possible loss of one or both photons from a pair are taken into account. Measured data provided by an intensified single-photon CCD camera are analyzed along the developed model. The joint signal-idler photon-number distribution is obtained using the expectation maximization algorithm. Covariance of the signal and idler photon-numbers equals 80 %. Statistics of the generated photon pairs are identified to be Poissonian in our case. Distribution of the integrated intensities of the signal and idler fields shows strong correlations between the fields. Negative values of this distribution occurring in some regions clearly demonstrate a nonclassical character of the light composed of photon pairs.
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Measurement of photon-number statistics of fields composed of photon pairs generated in spontaneous parametric down-conversion pumped by strong ultrashort pulses is described. Finite detection quantum efficiencies, noises as well as possible loss of one or both photons from a pair are taken into account. Measured data provided by an intensified CCD camera are analyzed along the developed model. The joint signal-idler photon-number distribution is obtained using the expectation maximization algorithm. Covariance of the signal and idler photon-numbers exceeds 98%. Entanglement area of the correlated photon pairs is determined.
We demonstrate, by direct measurement of the number of photons in signal and idler, that the twin-beam of light produced by ps-pulsed spontaneous parametric downconversion is endowed with sub-shot-noise photon-number correlations in a mesoscopic intensity regime (more than 1000 detected photons). The noise reduction, calculated from the variance of the difference in the numbers of detected-photons, resulted to be 3.25 dB below the shot-noise level. From experimental data we can recover joint photon-number distribution and a negative-valued joint signal-idler quasi-distributions of integrated intensities, which demonstrates the nonclassical character of the generated field.