  To evidence multimode spatial entanglement of spontaneous down-conversion,
detector arrays allow a 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 (EMCCD) cameras allow, in the present state of
technology, the detection of quantum correlations with the best signal-to-noise
ratio (SNR), while intensified CCD (ICCD) cameras allow at best to identify
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 not space-stationary
photon fluxes. Finally, experimental measurements of the SNR confirm our model.

Quantum Physics