Bell-state preparation using pulsed nondegenerate two-photon entanglement

We report a Bell-state preparation experiment. High-purity Bell states are prepared by using femtosecond pulse pumped nondegenerate collinear spontaneous parametric down-conversion. The use of a femtosecond pump pulse does not result in a reduction of quantum interference visibility in our scheme in which the postselection of amplitudes and other traditional mechanisms, such as using thin nonlinear crystals or narrowband spectral filters are not used. Another distinct feature of this scheme is that the pump, the signal. and the idler wavelengths are all distinguishable. which is very useful for quantum communications.