  Two-photon interference is a fundamental phenomenon in quantum mechanics and
stands at the base of numerous experimental observations. Here another
manifestation of this phenomenon is described, taking place at a Y junction.
Specifically it is shown how the r^2+t^2 term which is behind previous
observations of two-photon interference, may give rise to different states at a
beam-splitter and different two-particle transmission coefficients at a Y
junction. Different from previous descriptions of quantum transmission based on
one-particle physics, the enhanced transmission described here is due to
two-particle physics.
