Optimizing the signal-to-noise ratio in the measurement of photon pairs with detector arrays

To evidence multimode spatial entanglement of spontaneous down-conversion, detector arrays allowa full-field measurement, without any a priori selection of the paired photons. We show by comparing results of the recent literature that electron-multiplying CCD cameras allow, in the present state of technology, the detection of quantum correlations with the best signal-to-noise ratio (SNR), while intensified CCD cameras allow at best the identification of pairs. The SNR appears to be proportional to the square root of the number of coherence cells in each image, or Schmidt number. Then corrected estimates are derived for extended coherence cells and not-very-low and non-space-stationary photon fluxes. Finally, experimental measurements of the SNR confirm our model.