Response to "The physics of ghost imaging - nonlocal interference or local intensity fluctuation correlation?"

Shih has objected to the semiclassical explanation for lensless pseudothermal ghost imaging—whose measurement configuration is shown schematically in Fig. 8 of [1]—that is reviewed by Shapiro and Boyd. In Shih’s view, the only valid explanation for lensless pseudothermal ghost imaging is nonlocal two-photon interference, i.e., a purely quantum phenomenon. Shapiro and Boyd also develop that explanation for the lensless pseudothermal ghost image, where they show it to be equivalent, in its quantitative predictions, to the speckle-correlation interpretation arising from semiclassical photodetection theory. Thus, Sect. 1 of [1] concludes: “That the semiclassical and quantum theories yield identical measurements statistics in this case means that pseudothermal ghost-imaging experiments cannot distinguish between these two interpretations, even though we know that light is intrinsically quantum mechanical.” Shih begins by observing that Shapiro and Boyd fail to compare lensless pseudothermal ghost imaging of Scarcelli et al. [2], with the lens-based pseudothermal ghost