Highly efficient source for frequency-entangled photon pairs generated in a 3(rd)-order periodically poled MgO-doped...

We present a highly efficient source for discrete frequency-entangled photon pairs based on spontaneous parametric down-conversion using 3rd-order type-0 quasi-phase matching in a periodically poled MgO-doped stoichiometric LiTaO(3) crystal pumped by a 355.66-nm laser. Correlated two-photon states were generated with automatic conservation of energy and momentum in two given spatial modes. These states have a wide spectral range, even under small variations in crystal temperature, which consequently results in higher discreteness. Frequency entanglement was confirmed by measuring two-photon quantum interference fringes without any spectral filtering.