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Abstract
The quantum fluctuations of optical beams are highly correlated in electromagnetically induced transparency (EIT). The intensity fluctuations are enhanced by conversion of phase noise to intensity noise in atomic vapour. We have studied spectra of intensity fluctuations in dense rubidium vapour for different laser beam powers. Observed excess noise spectrum is broader than EIT window at the same optical power. Both spectral widths are proportional to the laser beam intensity. By using signal subtraction scheme we can reduce amplitude of the fluctuations to close the photonic short noise level. This result confirms the high degrees of intensity correlations and can be used to improve quality of optical atomic clocks.
Acknowledgements
We thank G.O. Ariunbold, I. Novikova, A.S. Zibrov and G.R. Welch for useful discussions. This work is supported by the Office of Naval Research, the NSF, the Air Force Research (Rome, NY), Defense Advanced Research Projects Agency-QuIST, Texas A&M University Telecommunication and Information Task Force Initiative, and the Welch Foundation (Grant A-1261).