Quantum interference: experiments and applications

We describe the simplest single-photon encoding schemes and introduce the concept of a quantum optical gate. These gates can be used to build up arbitrary entangled states of many initially separate single photons. Experimental realization of such a gate involves the development of nonlinear phase shift elements sensitive at the single quantum level. We report our experimental efforts using linear optical elements and non-classical sources where we are able to demonstrate interference and entanglement of initally separate single-photon pulses.