Experimental Generation of Narrow-Band Paired Photons: from Damped Rabi Oscillation to Group Delay

We report the experimental generation of narrow-band paired photons through electromagnetically induced transparency and spontaneous four-wave mixing in a two-dimensional magneto-optical trap (2D MOT). By controlling the optical depth of the 2D MOT from 0 to 40, the temporal length of the generated narrow-band paired photons can be varied from 50 to 900 ns. The 'transition' between damped Rabi oscillation and group delay is observed undisputedly. In the damped Rabi oscillation regime, a violation factor of the Cauchy-Schwartz inequality as large as 6642 is observed. In the group delay regime, sub-MHz linewidth (similar to 0.65 MHz) paired photons are obtained with a generation rate of about 0.8 x 10(5) s(-1).