W.A.T. Nogueira , S. P. Walborn, S. Pádua and C.H. Monken
PHYSICAL REVIEW LETTERS 86, 18 (2001)
We report an interference experiment that shows transverse spatial antibunching of photons. Using collinear parametric down-conversion in a Young-type fourth-order interference setup, we show interference patterns that violate classical Schwarz inequality and should not exist at all in a classical description.