Experimental progress in intracavity generation of squeezed light using resonant atomic nonlinearities

Quantum-noise reduction to levels nearly 1 dB below the standard quantum limit are reported for light frequencies near an atomic-sodium resonance. This squeezed light is generated in an optical confocal cavity using four-wave mixing due to the atomic-sodium resonance nonlinearity. Squeezed light exits the cavity through a partially reflecting mirror and is detected outside the cavity with a balanced homodyne detector. Experimental details are described for minimizing losses in the atomic beam and detection apparatus. Frequency jitter due to the pump laser also plays a key role in the limits for noise reduction. A wideband phenomenological model is used to analyse the results. Good agreement between this model and the experimental results is obtained. A full quantum model also agrees with the results and predicts even larger squeezing at higher pump intensities. Prospects for achieving this larger-noise-reduction regime are good.