Generation of two-photon entangled states through a cascaded nonlinear optical process in a quasiperiodic optical superlattice

The search for new methods to produce entangled photons is a subject of great interest in quantum optics. We show theoretically that two-photon entangled states may be generated through a cascaded nonlinear optical process in a quasiperiodic optical superlattice. When an idler photon (vi produced from spontaneous parametric down conversion (omega(p) = omega(s) + omega(i)) combines with a pump photon to produce a sum frequency photon omega(b) ( omega(b) = omega(i) + omega(p)), the latter is entangled with the remaining signal photon omega(i). Both a pulsed and a cw 532nm laser have been used to pump a quasi-phase matched LiTaO3 crystal to generate simultaneously 630nm signal photons through parametric down conversion and 460nm sum frequency photons. The advantage of this method is that entangled photons of short wavelength may be produced.