We demonstrate that the noise in the light from a high-efficiency light-emitting diode can be reduced below the classical shot noise limit when it is driven by a Johnson-noise-limited high-impedance source. A noise power reduction factor (Fano factor) of 0.96 has been achieved over a broad bandwidth from selected devices. The noise reduction is, in theory, only limited by the quantum efficiencies of emission, collection and detection of the light.
Two highly noise-correlated light beams are generated by nondegenerate parametric downconversion. %'e report the production of sub-Poissonian light in one of the beams by using negative feedback (to the pump) from the other. This nonclassical light source has a postdetection Fano factor of 0.78 over a limited frequency range near 50 Hz with an intensity of about 60 p%.
The master equation for optical bistability in the bad cavity limit is solved directly when the number of atoms is small. A necessary condition for bistability is given. In contrast to the semi-classical analysis, there is no sense in which there is bistability for 4 atoms; rather the order of 12 atoms is needed.
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