Light transmitted through a resonant atomic system with electromagnetically induced transparency displays reduced phase-noise fluctuations. For the case of the medium being inside a cavity, a 50% squeezing of the out-of-phase component is possible outside the cavity.
It has been shown by Imamoglu, Field and Harris1 that electromagnetically induced transparency can be used to achieve laser action without inversion. We have analyzed the quantum noise properties of the laser without inversion and shown that the intensity fluctuations in the laser output may be reduced 50% below the shot noise limit2. In recent work Makuta, Marmet and Stoicheff3 have shown that a resonantly enhanced second order susceptibility with reduced absorption at the second reduced harmonic wavelength may be achieved by electromagnetically induced transparency induced with a dc-electric field. We have calculated the photon statistics of the second harmonic light and found that near 100% amplitude squeezing can be achieved in the output at the second harmonic. We have shown that driven A model atoms in an optical cavity can reduce the amplitude fluctuation of a strong coherent input light field into the cavity by almost 100% without significantly depleting the input signal.
We demonstrate and characterize two coherent phenomena that can mitigate the effects of laser phase noise for electromagnetically induced transparency (EIT): a laser-power-broadening-resistant resonance in the transmitted intensity cross correlation between EIT optical fields, and a resonant suppression of the conversion of laser phase noise to intensity noise when one-photon noise dominates over two-photon-detuning noise. Our experimental observations are in good agreement with both an intuitive physical picture and numerical calculations. The results have wide-ranging applications to spectroscopy, atomic clocks, and magnetometers.