Abstract

A number of unusual optical interference effects have been observed that involve pairs of photons and cannot be understood or described in terms of classical electromagnetic waves. They include fourth-order interference of >50% visibility, which is unchanged when one of the beams is attenuated tenfold; measurement of the time interval between two photons with femtosecond accuracy; demonstration of phase memory in the two-photon down-conversion process due to vacuum entanglement.

© 1989 Optical Society of America