  We wish to report an experimental observation of anti-correlation from
first-order incoherent classical chaotic light. We explain why the classical
statistical theory does not apply and provide a quantum interpretation. In
quantum theory, either correlation or anti-correlation is a two-photon
interference phenomenon, which involves the superposition of two-photon
amplitudes, a nonclassical entity corresponding to different yet
indistinguishable alternative ways of producing a joint-photodetection event.
