  We report on an experimental observation of a two-photon ghost interference
experiment. A distinguishing feature of our experiment is that the photons are
generated via a non-degenerated spontaneous four-wave mixing process in a hot
atomic ensemble; therefore the photon has narrow bandwidth. Besides, there is a
large difference in frequency between two photons in a pair. Our works may be
important to achieve more secure, large transmission capacity long-distance
quantum communication.
