Quantum interference approach to two-photon correlation phenomena of chaotic light

We present a quantum two-photon interference approach to two-photon correlation phenomena of chaotic light, including the historical experiment of Hanbury Brown and Twiss. We argue against the interpretation of such phenomena in terms of a classical statistical correlation between intensity fluctuations. To support our view, we show a 'ghost' imaging experiment with chaotic light for which the classical understanding does not give a satisfactory interpretation. We also provide a two-photon optical picture of ghost imaging with chaotic light in terms of two-photon phase-conjugate mirrors which is very advantageous because it yields lensless two-photon imaging, suggesting imaging applications for radiations for which no effective lens is available.