The effects of preparing the atomic system in a coherent superposition of states in a number of optical systems are investigated. In particular, its applications with reference to phase-sensitivity and consequently, to noise quenching beyond the quantum limits are studied. Since the quantum noise arises from spontaneous emission fluctuations in all the optical systems, circumventing the quantum limits requires a modification of the spontaneous emission rate. To begin with, the simplest system is discussed, namely, a single two-level atom interacting with a single mode of radiation field in an ideal cavity. It is shown that the atomic superposition of states leads to a phase-sensitive dynamics of the atom as well as the spectral distribution of the field. A two-level linear amplifier based on phased atoms in pairs is discussed next. Such an amplifier feeds unequal noise to the two quadrature phases of the signal and for a certain choice of various parameters, the additive noise due to spontaneous emission in one of the quadratures is shown to vanish. Finally, a nonlinear theory of a correlated emission laser is presented.
展开▼
