2-PHOTON INTERFERENCE IN A STANDARD MACH-ZEHNDER INTERFEROMETER

A pair of light quanta with different colors (155.9-nm difference in c enter wavelength) generated from parametric down-conversion was inject ed collinearly into one input port of a Mach-Zehnder interferometer. C oincidence interference behavior was studied over a wide range of opti cal path differences of the interferometer. A measurement of 75% inter ference visibility with oscillation of the pump frequency for a large optical path difference of the interferometer (43 cm) is the signature of a quantum two-photon entangled state, which reflects both particle and wave nature of the light quanta in one experiment.