Strong low-frequency quantum correlations from a four-wave-mixing amplifier

Using a simple scheme based on nondegenerate four-wave mixing in a hot vapor, we generate bright twin beams which display a quantum noise reduction in the intensity difference of more than 8 dB. The absence of a cavity makes the system immune to external perturbations, and strong quantum noise reduction is observed at frequencies as low as 4.5 kHz and over a large frequency range.