Generation of narrow-band single-photon states via spontaneous parametric down-conversion for quantum memories in doped crystals

We present experimental results on the generation of narrow-band single-photon states via cavity-enhanced spontaneous parametric down-conversion in a PPLN crystal and demonstrate the feasibility of conditional preparation of single 867-nm photons with a 70-MHz linewidth, compatible with optical quantum memory devices based on Nd³⁺-doped isotopically pure Y⁷LiF₄ crystals.