CAN 2-PHOTON INTERFERENCE BE CONSIDERED THE INTERFERENCE OF 2 PHOTONS

We report on a ''postponed compensation'' experiment in which the obse rved two-photon entangled state interference cannot be pictured in ter ms of the overlap of the two individual photon wave packets of a param etric down-conversion pair on a beam splitter. In the sense of a quant um eraser, the distinguishability of the different two-photon Feynman amplitudes leading to a coincidence detection is removed by delaying t he compensation until after the output of an unbalanced two-photon int erferometer.