Photon bunching and multiphoton interference in parametric down-conversion

A number of multiphoton interference schemes involving independent fields f rom parametric down-conversion are analyzed. They include fourth-order (two -photon) interference between two fields from two independent parametric do wn-conversion processes, interference with two independent single photon Fo ck states (produced by gated parametric down-conversion), and quantum state teleportation and entanglement swapping. It is shown that the visibility i n these interference experiments is related to a quantity that is responsib le for the photon bunching effect in one of the fields (signal or idler) fr om the parametric down-conversion process. Besides the two-photon interfere nce schemes, a four-photon interference scheme is discussed where we consid er four-photon partition at a beamsplitter. It is found that probability di stribution of the partition is dramatically changed by four-photon interfer ence of six paths and the four-photon effect also depends on the same quant ity responsible for photon bunching. We will discuss the difference between two-photon interference and four-photon interference.