Bright correlated twin beams from an atomic ensemble in the optical cavity

We investigate the generation of bright correlated anti-Stokes and Stokes light beams with Doppler-broadened four-level atoms inside an optical ring cavity. By manipulating the large dispersion of the intracavity atomic medium near the electromagnetically induced transparency condition, the generated anti-Stokes and Stokes light fields can be made simultaneously on resonance with the cavity and to oscillate above threshold with narrowed linewidths. Noise correlation and violation of the Cauchy-Schwarz inequality with the two generated twin beams above the oscillation threshold at zero time delay are experimentally demonstrated.