: Does anybody know where I can find some info on photon entanglement. This is for a seminar in physics class so I would like to know how exactly you entangle a photon.

Yes. There are certain nonlinear (BBO) crystals, such as are used in optical parametric oscillators, that will supply entangles photon pairs. They are know as photon down converters. Down conversion is a phenomenon known to microwave waveguides researchers/engineers. Most of these crystals are quite hygroscopic and degrade with use requiring repolishing. There are a number of compounds that yeild nonlinearity. A rare earth is typically one of the components. Basically what happens is a photon of wavelength x enters the crystal and two photons of wavelength 2x exits. This of course conserves the total energy equation. The two photons are "entangled" the detextion of one implies the existance of the other. This can be used to obtain "which way" information for the "other" photon without "touching" it. Some very experiments and devices can be contrived as a result.