Figure 1.

Measuring the biphoton joint probability distribution with an EMCCD camera. (a) Experimental setup for measuring far-field type-I SPDC. (b–e) Flow chart of data processing. (b) The camera acquires many thresholded frames from which we calculate both (c) the average of all frames 〈$C_i$〉 (indicated by 〈·〉) and (d) the average of the tensor product of each frame with itself 〈$C_{ij}$〉 (⊗, Eq. (2)) (shown here for $j=[x_j=70,y_j=33]$, indicated by the blue ×). Most coincidences are accidentals between photons from different pairs, yielding the apparent similarity between (c) and (d). Genuine coincidences from anticorrelated entangled photons appearing within the boxed region give a difference between the two (see insets). (e) The conditional probability distribution, via Eq. (4), shows anti-correlation of paired photons localized about $i$ = [−70, −32].