Narrowband photon pair generation and waveform reshaping

In this article, we review on narrowband photon pairs producedin nonlinear crystals, and especially in atomic ensembles. In atomicensembles, “write-read” process in pulse mode andspontaneous four-wave mixing process (SFWM) in continuous mode aretwo popular photon pair generation schemes. We specifically discussthe experimental works with continuous SFWM scheme in cold atomicensembles. Photon pairs produced in these systems are characteristicof controllable long coherence time, and therefore are accessiblewith direct temporal modulation. We elaborate on the recent techniqueson modulation and waveform reshaping of narrow-band paired photons.